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How the atmosphere sustains life on Earth

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Earth is a vibrant blue planet, the only place that we can be sure that life exists. As A Perfect Planet shows, a complex and interconnected set of systems operate to form our environment. Every planet except one in the Solar System has a gaseous atmosphere , as do some moons and even some dwarf planets. Why does the Earth’s atmosphere make it so perfect as a home for life?

The Earth’s atmosphere

The atmosphere is thin and light, a gas that is only bound to the solid mass of the Earth by gravity. The mass of the atmosphere is about 250 times less than that of the oceans and accounts for less than one millionth of the total mass of the planet. The atmospheric pressure and density of air decrease exponentially with height above the surface. The term ‘exponentially’ means that for every increase in height by the same distance, the atmospheric density falls by the same factor. In the case of the Earth, density halves for every increase of around 5.9 km in altitude. At the top of Mount Everest (8.85 km above sea-level), about 70% of the atmosphere is already beneath your feet. Contrast this with the radius of the Earth itself, around 6,371 km. The atmosphere is really a very thin skin.

The image above was taken by an astronaut on the International Space Station as the Sun sets behind the outer edge of the Earth. Astronauts aboard the International Space Station experience sixteen sunsets and sunrises per day as it orbits Earth! The lowest layer of the atmosphere is mostly illuminated red and is cloudy in this image. This is the troposphere, where the atmosphere churns as it carries heat upwards by convection from the surface, like water in a saucepan when heated from below. The troposphere is where nearly all of our familiar weather happens. Long-distance passenger aircraft fly in the upper troposphere. The troposphere extends to about 10–20 km from the surface; it is up to 20 km deep near the equator, where the atmosphere is convecting strongly, and can be as little as half that at the poles. Within the troposphere the temperature falls by about 6°C for every kilometre of altitude gained, so by the top of the troposphere the temperature can fall well below -80°C and the pressure and density are only a tenth of those at the surface. These conditions require a pressurised and heated cabin or a space suit.

The atmosphere above the troposphere is called the stratosphere and appears a clear, blue colour in the image. In the stratosphere the temperature begins to rise again with increasing height. In contrast to the troposphere, the stratosphere is very stable, or stratified, as implied by the name. Although 90% of the mass of the atmosphere is below in the troposphere, the stratosphere still makes a vital contribution to the environment beneath. Only a few aircraft and research balloons are built to be able to fly in the stratosphere in the thin air. Most of the sky would already be dark, rather than blue, for a passenger in such an aircraft. The top of the stratosphere lies at about 50 km altitude. Although there are more rarefied atmospheric layers above, for practical purposes the environment is already much more like ‘space’ by this point. By convention ‘space’ is said to start at an altitude of 100 km, although this is a rather arbitrary round number and there is no ‘top’ to the atmosphere as such, rather atoms and molecules simply become increasingly rare, but a very few reach out even beyond the Moon’s orbit and are lost to Earth.

The connected environment

A Perfect Planet emphasises how different elements of our environment are interconnected. The atmosphere responds to varying heating by sunlight, driving movement. These motions in the troposphere are what we experience as wind. The oceans supply water vapour, which absorbs and releases heat, forms clouds and scatters sunlight. The patterns of continents, oceans and sea ice at the surface determine the heating that drives the troposphere from below. Volcanic activity has outgassed the atmosphere itself from the body of the forming planet and continues to supply many trace gases and small particulates to the mix. Variations in volcanic output are connected to sometimes huge climate changes. Life has modified the composition of the atmosphere, resulting in the present range of gases, which is very different to the carbon dioxide-dominated atmospheres of Venus and Mars. Now humans are leaving our own mark in pollutants and greenhouse gases.

But despite being so thin and light, the atmosphere is far from insignificant. The influence is not all in one direction and the atmosphere plays a vital role in the evolution of the other elements. Winds drive ocean currents and rainfall alters ocean salinity and so density, which drives other, deep circulation patterns. Atmospheric transport spreads volcanic outputs over wide areas. The climate change resulting from the atmospheric response to volcanic gases and aerosols is thought to have melted the ice in periods when Earth was deep-frozen and to have caused mass extinctions several times in the past. The atmosphere today is both a consequence of, and essential for, life.

A deep breath

A basic necessity for humans is to breathe oxygen at a sufficient pressure for our respiratory system to work. Complex, multicellular life on Earth needs an atmosphere for either respiration or photosynthesis. Even aquatic species rely on dissolved oxygen from the air. Photosynthesis, in contrast, requires carbon dioxide, also from the atmosphere. To survive, both animals and plants need a considerably larger mass of air per day than they do food or drink, typically by about five times for humans.

The oxygen in our atmosphere was first produced in large quantities by simple, single-celled cyanobacteria about 2–3 billion years ago. After this ‘Great Oxygenation Event’ many more complex, multi-celled organisms were able to evolve to take advantage of the changed environment.

The weather

One way that the atmosphere impacts us all is through ‘weather’. Weather is simply the day-to-day change in the atmosphere around us. The atmosphere changes rapidly because it has a relatively low density and, as a gas, it is able to flow freely. Change in the oceans or the rocky surface of the Earth happens over longer timescales. Weather affects nearly all human occupations. Agriculture, construction, travel and the leisure industries, all depend on the weather in various ways. Hence, reliable weather prediction is vital. It is difficult to think of any occupation that might not benefit from a weather forecast: even astronauts require detailed forecasts for launch and re-entry.

The weather has been a source of power for human civilizations, from windmills and sailing ships to modern turbines for renewable energy. The atmosphere itself converts heat energy from the Sun into motion as winds. People have learned to convert some of this wind energy into electricity or use it for other mechanical work, such as pumping or milling. Of course, we are not the only life form to make use of wind energy. Plants can use it to disperse their seeds more widely, for example.

The water transporter

The atmosphere is vital for all life on the planet, not only humans, and for reasons other than supplying gases needed for respiration and photosynthesis. Winds also transport water into the interiors of large areas of land, which would otherwise rapidly become parched desert. This supply of fresh water is essential to life on Earth. An illustration of the importance of rainfall patterns is clearly seen in the image below, obtained from a geostationary weather satellite.

The central region of Africa, around the equator, is bright green with lush vegetation. The reason is clearly visible as it is also almost covered by white, convective clouds in the image. These grow during the day, as the surface warms in the sunlight, and typically produce rain in the afternoons, supplying water to the plants and animals which live below. A similar process occurs to the left of the disc in South America, where the rainforest is drained by the great Amazon basin. To the south and north of the equatorial region lie vast areas of dry, yellowish brown desert. Most obvious is the Sahara Desert in North Africa, just above the centre of the image. These areas are relatively cloud-free and there is little rainfall. The reason is that air which has risen from the surface at the equator has already lost much of its water content as the vigorous equatorial clouds condense. This dry air reaches the top of the troposphere, turns north or south, and then descends to the surface again. This circulation pattern is known as a Hadley cell. The deserts appear in the regions of dry, descending air, which no longer has sufficient water content to form clouds.

Further north, Europe is also supplied with water, perhaps in the form of snow on mountains at this time of year, from a bank of clouds in the image. These occur as a result of a different weather process as weather systems move from west to east across the North Atlantic. Low pressure, cyclonic systems can be seen as spirals of cloud, rotating in an anti-clockwise sense in the northern hemisphere, under the influence of the Earth’s rotation.

The different weather patterns at different latitudes on the Earth are all part of the atmosphere’s response to solar heating. The consequent patterns of rainfall determine what type of life can flourish in different regions. Without resupply by rain or snow, the centres of continents would be arid, and life would struggle to survive.

The atmosphere also shields life. Many small rocks are littered throughout the Solar System, left over from the violent processes that occurred during its formation or formed in subsequent collisions between objects. Small rocks, called meteoroids, frequently encounter the Earth. Most burn up when they enter the atmosphere and do not reach the ground, often called ‘shooting stars’ or meteors. Even rocks as large as one kilometre across tend to break up and only smaller fragments (meteorites) reach the ground, with less devastating consequences than might otherwise occur.

The shielding role of the atmosphere crucially extends to electromagnetic radiation. Electromagnetic waves occur on a spectrum ranging from very short wavelength waves, such as gamma- and X-rays, to long wavelengths, such as microwaves and radio waves. One very small region of the electromagnetic spectrum is known as ‘light’, at wavelengths that our eyes can detect. The wavelength of visible light ranges from about 0.4 mm (which we see as violet) to about 0.7 mm (which we see as red). The colours of the rainbow fall between these two wavelengths. The symbol mm means a millionth of a metre and is called a ‘micrometre’, or often just a ‘micron’. For comparison, a bacterium is about 1 mm across, a human red blood cell is about 10 mm and a human hair is typically 100 mm wide.

We think of air as transparent, but actually it is almost opaque to electromagnetic waves at many wavelengths. The visible region is an exception, often called a ‘window’. This is why animal eyesight normally operates on wavelengths around this region. Other ‘windows’ exist and are used for radio signals, for example, but the atmosphere protects life from many shorter wavelengths that are often harmful to cell structures.

The Sun emits a variety of electromagnetic waves, but most of its energy is in the visible range and at shorter ultraviolet wavelengths. Ultraviolet waves, with wavelengths of about 0.2–0.4 mm, can be extremely dangerous, damaging genetic material and causing cancers. Atoms and molecules in the atmosphere scatter short wavelengths and some gases, mainly ozone, absorb ultraviolet radiation in the most damaging wavelength region. Almost no solar radiation at wavelengths shorter than about 0.3 mm reaches the surface as a result of this scattering and ozone absorption. Were this not the case, as on planets without a substantial amount of ozone, life might only be possible underground. It is this absorption of ultraviolet light by ozone that explains why the Earth’s stratosphere gets warmer with increasing altitude, as described earlier. The scattering of shorter wavelengths also explains the beautiful blue colour of a clear sky.

The natural greenhouse

The Earth also emits electromagnetic waves, but at its cooler temperature these are at a longer wavelength of around 10 mm, known as the thermal infrared region. The atmosphere is not completely transparent to thermal infrared radiation, and several gases (including methane, nitrous oxide, water vapour and carbon dioxide) absorb energy in the wavelength range of 1–20 mm. This energy is re-emitted by the atmosphere and causes the well-known ‘greenhouse effect’ (confusingly, this is not how garden greenhouses actually work, they mainly act to suppress vertical convection and block the escape of air and heat from the warm surface).

The natural greenhouse effect from the present-day atmosphere on Earth is equivalent to about 33 °C of warming at the surface. The average (over time of day, season and all locations) surface temperature of the Earth is around 14 °C. If the atmosphere were truly transparent at all wavelengths, the surface temperature would fall to -18 °C on average. Lakes and seas would remain frozen over. It seems unlikely that complex life would have developed without easy access to liquid water at the surface. That the Earth supports water in all three phases (solid ice, liquid water and water vapour), at various locations on the surface of the planet, is a unique feature in the present-day Solar System. Water occurs throughout the Solar System, but on no other planet or moon can liquid water persist at the surface without freezing or boiling.

The heat engine

It is interesting to compare temperatures on the Earth and the Moon’s surface. The Moon is, on average, the same distance from the Sun and is made of dark rock. In the day, the surface temperature can reach 130 °C and then fall to -175 °C at night. This huge cycle of over 300 °C is far greater than is seen anywhere on Earth, and it might appear surprising even given the Moon’s longer diurnal cycle (the Moon rotates once every 27 days). That we experience a far more moderate day/night difference in temperature is mostly due to the effect of the atmosphere. The movement of air can transport heat into a region in darkness, and back-scattering of infrared radiation can keep the surface there warmer than if it all escaped to space. One familiar example is that surface frosts more often appear after a clear night compared to a cloudy one, when more infrared radiation is scattered back by cloud particles.

Although the atmosphere is only a small proportion of the mass of the Earth, its rapid response to heating variations means that it transports an enormous amount of heat. The weather systems discussed in relation to water transport above exist because of the thermal contrast between the equator and poles. They transport heat from warmer to cooler regions. A heat engine is simply a device that converts heat energy to kinetic energy and this is the same process that powers winds. In total, the atmosphere transports about 5 PW (5 petawatts or 5,000,000,000,000,000 watts) of power. This is roughly 250 times the total power consumed by humans today in all forms. This heat transport means that the equator is cooled and the polar regions are warmed very significantly. The Moon lacks similar heat transport. Temperatures of -247 °C have been recorded in craters near the poles of the Moon that get very little sunlight. This temperature is low compared even to Pluto. Nitrogen freezes at about -210 °C and oxygen at -219 °C. If Earth’s poles were to get this cold, then the atmosphere itself would freeze into ice around the poles, precipitating a calamitous atmospheric collapse. Less dramatically, the enormous poleward heat transport by the existing atmosphere keeps high latitude regions warm enough, and equatorial regions cool enough, to remain hospitable environments for life.

The atmosphere: friend or foe?

This article has discussed why the atmosphere is beneficial for life , but weather can also be deadly. Even apparently destructive aspects may have benefits to life on the planet as a whole; life evolves under the stresses of a changing environment. The ‘Great Oxygenation Event’ of the atmosphere led to the development of respiration, employed by animals today. But it was also a ‘Great Oxygenation Catastrophe’ that poisoned many other simple lifeforms at the time. Great extinctions of life are linked to past climate changes. It is a sobering thought that we owe our entire existence, and that of all the large plants and animals with which we are familiar, to a tenuous layer of gas only a few kilometres thick above our heads.

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• Originally published: Monday, 2 November 2020
• Body text - Creative Commons BY-NC-SA 4.0 : The Open University
• Image 'Earth from MSG-4' - Copyright: © Eumetsat (2019)
• Image 'Sunset looking through the Earth’s atmosphere from the International Space Station' - Copyright: © NASA
• Image 'Arrival of a Soyuz spacecraft at the International Space Station against the backdrop of the Earth’s limb with some towering cumulus clouds.' - Copyright: © ESA/NASA
• Image 'Climate change' - Copyright: Used with permission
• Image 'Galaxies, stars and planets' - Copyright: Used with permission
• Image 'Particle physics' - Copyright: © Thomas Jurkowski | Dreamstime.com

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Essay on Atmosphere

Students are often asked to write an essay on Atmosphere in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Atmosphere

Introduction to atmosphere.

The atmosphere is the layer of gases that surrounds the Earth. It’s vital for life because it provides the air we breathe and protects us from harmful radiation.

Components of Atmosphere

The atmosphere is made up of many gases. About 78% is nitrogen, 21% is oxygen, and the rest includes gases like carbon dioxide and argon.

Atmosphere Layers

The atmosphere has five main layers. These are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Each has unique characteristics and importance.

Atmosphere’s Role

The atmosphere plays a key role in climate and weather patterns. It also helps protect Earth from meteoroids.

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250 Words Essay on Atmosphere

The atmosphere, a critical component of the Earth’s system, is a thin layer of gases that envelops our planet. It functions as a protective shield, maintaining the balance of life-sustaining conditions and protecting us from harmful cosmic radiation.

Composition of the Atmosphere

Primarily composed of nitrogen (78%) and oxygen (21%), the atmosphere also contains trace amounts of other gases like argon, carbon dioxide, and neon. Water vapor and aerosols are variable constituents, influencing weather and climate patterns.

Layers of the Atmosphere

The atmosphere is stratified into five main layers based on temperature variations. The troposphere, where weather events occur, is the layer closest to Earth. Above it lies the stratosphere, home to the ozone layer. The mesosphere, thermosphere, and exosphere follow, each with unique characteristics.

Role in Climate Regulation

The atmosphere plays a significant role in climate regulation. It absorbs and redistribits solar energy, maintaining Earth’s temperature. Greenhouse gases in the atmosphere trap heat, a natural process essential for life but exacerbated by human activities, leading to global warming.

Atmospheric Pollution

Human activities have led to increased atmospheric pollution. Emissions from industries, vehicles, and deforestation increase the concentration of greenhouse gases, contributing to climate change. This highlights the urgent need for sustainable practices to mitigate atmospheric damage.

Understanding the atmosphere’s composition, structure, and functions is crucial for addressing environmental challenges. As stewards of the planet, we must strive to reduce our impact and preserve the atmosphere for future generations.

500 Words Essay on Atmosphere

The atmosphere, a vital component of our planet, is a complex layer of gases that envelops the Earth, protecting life and facilitating various processes. It primarily consists of nitrogen (78%) and oxygen (21%), with the remaining 1% comprising a mix of argon, carbon dioxide, neon, helium, and other trace gases. The atmosphere’s importance is manifold, from providing the air we breathe to shielding us from harmful solar radiation.

The atmosphere is not a homogeneous entity but is divided into five distinct layers based on temperature variation. The closest to the Earth’s surface is the Troposphere, where weather phenomena occur. Above it lies the Stratosphere, home to the ozone layer. The Mesosphere, the third layer, is where most meteors burn up upon entry. The Thermosphere, known for its high temperatures, houses the International Space Station in its uppermost region. Lastly, the Exosphere forms the outermost layer, gradually fading into outer space.

Atmospheric Dynamics

The atmosphere is a dynamic system, constantly interacting with other Earth’s spheres, like the hydrosphere, lithosphere, and biosphere. This interaction is crucial for various processes, such as weather formation, climate regulation, and life sustenance. The Sun’s heat causes atmospheric and oceanic circulation, influencing weather patterns and climate zones. The atmosphere also plays an integral role in the water cycle, facilitating the transportation and redistribution of water across the globe.

The Atmosphere and Climate Change

In recent years, the atmosphere’s role in climate change has been under intense scrutiny. Human activities, especially the burning of fossil fuels, have led to an increase in greenhouse gases in the atmosphere. These gases trap heat, causing a rise in Earth’s average temperature, a phenomenon known as global warming. This has led to a cascade of effects, including melting polar ice, rising sea levels, and increased frequency of extreme weather events.

Conclusion: The Need for Atmospheric Conservation

In conclusion, the atmosphere is a critical component of Earth’s system, with a pivotal role in sustaining life and maintaining global processes. However, human-induced changes threaten its balance, leading to dire global consequences. Therefore, it is imperative to understand and respect the intricate dynamics of the atmosphere and strive towards its conservation. By adopting sustainable practices and reducing greenhouse gas emissions, we can ensure the preservation of this vital resource for future generations.

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Importance of the Earth's Atmosphere

How the Atmosphere Protects the Earth

Without the protective layer of gases that make up Earth's atmosphere, the harsh conditions of the solar system would render the planet a barren, lifeless husk like the moon. The Earth's atmosphere protects and sustains the planet's inhabitants by providing warmth and absorbing harmful solar rays. In addition to containing the oxygen and carbon dioxide, which living things need to survive, the atmosphere traps the sun's energy and wards off many of the dangers of space.

Temperature

One of the most important benefits the atmosphere provides is maintaining the Earth’s temperature. On the moon, which has no protective atmosphere, temperatures can range from 121 degrees Celsius in the sun (250 degrees Fahrenheit) to negative 157 degrees Celsius in the shade (negative 250 degrees Fahrenheit). On Earth, however, molecules in the atmosphere absorb the sun’s energy as it arrives, spreading that warmth across the planet. The molecules also trap reflected energy from the surface, preventing the night side of the planet from becoming too cold.

The atmosphere serves as a protective shield against radiation and cosmic rays. The sun bombards the solar system with ultraviolet radiation, and without protection, that radiation can cause severe damage to skin and eyes. The ozone layer high in the Earth’s atmosphere blocks much of this radiation from reaching the surface. Dense layers of molecular gases also absorb cosmic rays, gamma rays and x-rays, preventing these energetic particles from striking living things and causing mutations and other genetic damage. Even during a solar flare, which can greatly increase the damaging output of the sun, the atmosphere is able to block most of the harmful effects.

Physical Protection

The solar system may seem like a vast and empty place, but in reality it is full of debris and small particles leftover from planetary creation or collisions in the asteroid belt. According to NASA, more than 100 tons of space debris strikes Earth every single day, mostly in the form of dust and tiny particles. When they encounter the molecules that make up Earth’s atmosphere, however, the resulting friction destroys them long before they reach the ground. Even larger meteors can break up due to the stresses of atmospheric re-entry, making catastrophic meteor strikes an incredibly rare occurrence. Without the physical protection of the atmosphere, the surface of the Earth would resemble that of the moon, pockmarked with impact craters.

Weather and Water

The atmosphere also serves an important purpose as a medium for the movement of water. Vapor evaporates out of oceans, condenses as it cools and falls as rain, providing life-giving moisture to otherwise dry areas of the continents. According to the U.S. Geological Survey, the Earth’s atmosphere holds around 12,900 cubic kilometers (3,100 cubic miles) worth of water at any given time. Without an atmosphere, it would simply boil away into space, or remain frozen in pockets below the surface of the planet.

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• NASA: Goddard Space Flight Center: Moon Facts
• NASA: Goddard Space Flight Center: Danger of Solar and Cosmic Radiation in Space
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• NASA: Jet Propulsion Laboratory: Near Earth Object Program
• U.S. Geological Survey: The Water Cycle

About the Author

Milton Kazmeyer has worked in the insurance, financial and manufacturing fields and also served as a federal contractor. He began his writing career in 2007 and now works full-time as a writer and transcriptionist. His primary fields of expertise include computers, astronomy, alternative energy sources and the environment.

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93 Atmosphere Essay Topic Ideas & Examples

🏆 best atmosphere topic ideas & essay examples, 📌 simple & easy atmosphere essay titles, 👍 good essay topics on atmosphere, ❓ essay questions about atmosphere.

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• The Problem of Atmospheric Pollution in Modern World It speeds up the erosion of construction materials and the decomposition of metals which destructs the human respiratory system by introducing poisonous materials into the system. Afterwards, the use of vents and the burning of […]
• An Analysis of the Polar Regions and Atmosphere Composition in Mars
• The Rise of Carbon Dioxide in the Atmosphere: Causes and Potential Dangers
• Banded Iron Formations and the Evolution of the Atmosphere
• Water Isotopes in the Investigation of the Connection Between Atmosphere and Terrestrial Water Cycle
• Modification of the Natural Characteristics of the Atmosphere
• Changes in the Atmosphere Causing Multicellularity
• An Analysis of the Sources of Greenhouse Gases in the Atmosphere
• Modes of Variability in the Atmosphere
• The Two Exchange Systems That Alter the CO2 Concentration of the Atmosphere
• Exergy Balance of the Earth’s Surface and Atmosphere
• Anthropogenic and Natural Factor Associated With High GHGs Concentration in the Atmosphere
• Dynamic Meteorology and the Study of the Motions of the Atmosphere
• The Chemical Composition of the Atmosphere
• Studying the Processes of Heating and Cooling of the Atmosphere
• Research of the Earth’s Oceans and How They Affect the Atmosphere
• Evolution of Earth-Like Extrasolar Planetary Atmospheres
• Atmospheric Acceleration and Earth-Expansion Deceleration of the Earth Rotation
• Spectroscopy of the Earth’s Atmosphere and Interstellar Medium
• Origin of the Atmospheres of the Earth and the Planets
• Atmospheric Drag Effects on the Motion of an Artificial Earth Satellite
• Water Formation in the Upper Atmosphere of the Early Earth
• Advanced Numerical Techniques for Modeling and Data Assimilation of Atmosphere and Oceans
• Analytical Advances to Study the Air–Water Interfacial Chemistry in the Atmosphere
• Nucleation in the Mediterranean Atmosphere
• An Analysis of Global Warming and the Greenhouse Effect in the Pollution of the Atmosphere
• The Role of the Global Climate and Atmosphere
• The Destruction of the Earth’s Atmosphere Due to Air Pollution
• Coupling between Plasmasphere and Upper Atmosphere
• Atmospheric Particle Pollution and Interactions With Meteorological Factors
• Observations and Analysis of Upper Atmosphere
• Chemical Composition and Sources of Particles in the Atmosphere
• Effect of Solar Activities to the Earth’s Atmosphere
• Impact of Ocean Plants on Atmosphere
• Impact of the Atmosphere on Quality of Life, Ecosystems, and Human Activities
• Research About Permafrost–Atmosphere Interactions
• Atmospheric Boundary Layer Processes, Characteristics and Parameterization
• Satellite Observations of Ocean–Atmosphere Interaction
• Impact of Volcanic Eruptions on the Atmosphere
• New Insights in the Modeling of Earth and Planetary Atmospheres
• Atmospheric Boundary Layer Observation and Meteorology
• Dynamics of Airborne Microplastics, Appraisal and Distributional Behaviour in Atmosphere
• What Prevents Atmospheric Gases From Flying off Into Space?
• How Has the Earth’s Atmosphere Evolved?
• What Are the Four Major Sections of the Atmosphere?
• How Does the Atmosphere Respond to Uneven Solar Heating?
• What Are the Three Most Abundant Gases in the Atmosphere?
• How Does Pollution Destroy the Atmosphere and Habitats?
• Why Was Earths Early Atmosphere Able to Support Photosynthesis?
• How Do the Ocean and Plants Affect the Removal of Carbon in Our Atmosphere?
• What Produced the Oxygen in Earth’s Atmosphere?
• How Do Greenhouse Gases Increase Atmosphere Temperature?
• What Percent of the Atmosphere Is Made of Trace Gases?
• How Do Two Gases Make up the Atmosphere?
• Where in the Atmosphere Is Water Vapor Most Concentrated?
• How Do the Troposphere and Ionosphere Affect Satellite Communication?
• What Ecosystem Services Does the Atmosphere Provide?
• How Does the Atmosphere Retain Itself?
• What Are Atmospheric Rivers?
• How Has Earth’s Atmospheric Composition Changed Over Time?
• What Is the Mesosphere?
• Why Doesn’t Thermal Stratification Occur in the Atmosphere?
• How Do Changes in Atmospheric Chemistry Impact the Greenhouse Effect?
• What Is Sink in Atmospheric Chemistry?
• How Was the Atmospheric Chemistry Different in Early Earth’s History?
• What Are Free Radicals in Atmospheric Chemistry?
• How Does Atmospheric Composition Affect Thermal Escape?
• What Is the Atmosphere Made of?
• When Was Atmospheric Chemistry Begun?
• What Ecological Goods and Services Does the Atmosphere Provide?
• Why Isn’t Earth’s Atmosphere Mostly Hydrogen?
• What Is the Composition of the Earth’s Atmosphere and How Life Affected the Atmosphere During the Past Several Billion Years?
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The Atmosphere: Earth’s Security Blanket

Sizing Up Humanity's Impacts on Earth's Changing Atmosphere​: A Five-Part Series

Most of us probably don’t think much about Earth’s atmosphere, let alone how much humans are affecting it. After all, it’s just there.

Gazing into the sky during the day, it’s tough to get a handle on what’s happening up there. Our atmosphere seems tantalizingly close and yet mysteriously distant. The life-sustaining air we breathe envelops our planet like a pale-blue security blanket, clinging to us by the force of gravity. We see birds, planes, an ever-changing patchwork of clouds and, in some places, air pollution. Farther out, our Moon glows down on us and a blazing Sun hangs in the sky. From our Earth-bound perspective, it’s hard to tell where our atmosphere ends and space begins. (Our atmosphere is like a multi-layered cake.)

Then darkness falls, and through the murky blackness, a portal opens to the heavens, punctuated only by the light of the Moon, stars and cosmos. The descent of night makes sizing up our atmosphere an even more baffling proposition.

It’s only when we view Earth from the unique vantage point of space that the true nature of our atmosphere becomes apparent. From Earth orbit, we gain a new window into our planet. Beneath us, the very edge of the atmosphere — known as Earth’s “limb” — appears as a glowing halo of colors; a luminescent layer cake that gradually fades into the blackness of space. And suddenly our atmosphere, which seemed so vast and mysterious from the ground, appears shockingly thin, even fragile .

So thought retired NASA astronaut Scott Kelly. As he neared the end of a one-year stay aboard the International Space Station in February 2016, he told CNN, "When you look at the ... atmosphere on the limb of the Earth, I wouldn't say it looks unhealthy, but it definitely looks very, very fragile and just kind of like this thin film, so it looks like something that we definitely need to take care of." Other NASA astronauts have made similar remarks.

Indeed, Earth’s atmosphere isn’t something we can take for granted. Without it, life as we know it wouldn’t exist. Not only does it contain the oxygen we need to live, but it also protects us from harmful ultraviolet solar radiation. It creates the pressure without which liquid water couldn’t exist on our planet’s surface. And it warms our planet and keeps temperatures habitable for our living Earth.

In fact, Earth’s atmosphere is very thin, with a mass only about one-millionth that of the planet itself. Further, about 80 percent of the atmosphere is contained within its lowest layer, the troposphere, which is, on average, just 12 kilometers (7.5 miles) thick.

While there’s no exact boundary line between the atmosphere and space, the accepted standard is about 100 kilometers (62 miles) above Earth’s surface. If you drove that distance on the ground, you might see a change in scenery. But travel that distance straight up, and you’ll quickly find yourself in an environment inhospitable to life. At about 8 kilometers (5 miles) altitude, there’s insufficient oxygen in the air to sustain human life. At around 19 kilometers (12 miles) altitude, your blood boils unless you’re in a pressurized environment.

So is Earth’s atmosphere big or small? Is it fragile or robust? Stable or volatile? And how much are humans affecting it, really?

The answer, it seems, is all of the above, and we’re affecting it a lot . In this five-part series, we asked several NASA atmospheric scientists to weigh in on the matter.

A ‘Radical’ Chemical That Helps Keep Our Atmosphere Stable

Before we can determine how fragile or stable Earth’s atmosphere is, we first have to define what those terms mean. So says Kevin Bowman of NASA’s Jet Propulsion Laboratory in Pasadena, California, principal investigator for the Tropospheric Emission Spectrometer (TES) instrument on NASA’s Aura satellite. TES operated from 2004 to early 2018.

“The chemistry of Earth’s atmosphere is remarkably stable, providing a relatively safe place for animals and plants to thrive,” said Bowman. “However, even small changes to the quality of the air that we breath can have profound impacts on our health. Understanding that stability, the ways it could be impacted by humans and how it interacts with the broader Earth system are key research tasks in atmospheric chemistry.”

Bowman said one key to that stability is the hydroxyl radical (OH), a chemical that plays a central role in the ability of Earth’s atmosphere to cleanse itself of pollutants. One of the most reactive gases in our atmosphere, OH is like a global detergent that helps keep things in balance by removing pollutants from the lower atmosphere. It’s the main check on concentrations of carbon monoxide, sulfur dioxide, hydrogen sulfide, methane and higher hydrocarbons.

Scientists have numerous questions about OH. They want to know how stable it is, how quickly it cleanses these chemicals from the atmosphere, and how the atmosphere’s cleansing capacity has changed in the past and may change in the future. They also want to know how climate change may affect OH’s stability. For example, continued increases in methane — a potent greenhouse gas — will consume OH, resulting in deteriorated air quality.

To predict changes in OH’s capacity to cleanse the atmosphere, scientists rely on atmospheric models based on data from satellites, aircraft and ground measurements. “Studies of ancient climates suggest these models are underestimating the sensitivity of OH to climate change,” said Bowman. “As a result, our atmosphere might be more variable than we thought, and OH could end up changing much more rapidly than predicted, with detrimental effects on Earth’s surface air quality, the concentration of greenhouse gases and ozone.”

Bowman said quantifying OH has always been challenging for scientists since it can’t be measured directly. In the past, scientists derived estimates of OH by tracking quantities of another trace gas, methyl chloroform, which was widely used in the 1950s as an industrial solvent and was created by bomb blasts during that era. Methyl chloroform only reacts with OH, which slowly destroys it. But methyl chloroform was eventually replaced by other solvents, and over time, its concentrations in the atmosphere have decreased enough that it is no longer useful for estimating OH.

Observations from instruments like TES give researchers an alternate approach to estimate OH through atmospheric computer models that produce “chemical weather forecasts.” TES measurements of a number of other chemical elements influenced by OH, such as ozone, carbon monoxide and nitrogen dioxide, have enabled scientists to better represent OH in these models. To date, studies based on TES data show there’s more OH in the northern hemisphere than in the southern hemisphere — consistent with methyl chloroform concentrations — and that OH is sensitive to changes in emissions, especially in the tropics.

Bowman discussed some of the many other science advances TES has made possible. Its biggest contributions have been in advancing our understanding of ozone in the troposphere. TES data, together with data from other instruments aboard Aura, have significantly improved our understanding of how ozone affects human health, climate and other parts of the Earth system. A 2015 TES study showed how ozone produced in Asia was transported around the world, increasing ozone emissions on the U.S. West Coast, even as U.S. ozone emissions were declining. TES data also helped quantify how ozone in the upper troposphere serves as a greenhouse gas, warming the atmosphere. This information was used to test climate model predictions of ozone’s greenhouse effect, quantifying how regional changes in pollutants that create ozone have altered climate. TES measurements have also improved our understanding of global air quality by documenting increases in tropospheric ozone levels in many regions of the world, such as Asia.

“We’re beginning to see a redistribution in the emissions of pollutants that form ozone,” Bowman said. “They’re shifting geographically toward the equator, making ozone a more potent greenhouse gas.”

Bowman said TES has also given us a window into Earth’s water cycle by measuring so-called “heavy” water molecules, a naturally occurring variant of water that contains more neutrons than normal water molecules and provide clues to how the water evaporated and fell as precipitation in the past. This, in turn, helps scientists understand what controls the amount of water vapor in the atmosphere. A study using these data showed how the Amazon initiates its own rainy season.

In addition, TES provided new information about ammonia, a precursor to harmful aerosols; and new measurements of carbon-containing gases such as methane and carbonyl sulfide, giving scientists new insights into the carbon cycle.

“TES was a pioneer,” Bowman said. “It collected a whole new set of measurements using new techniques that are now being used by a new generation of instruments.”

To learn more about TES, visit https://tes.jpl.nasa.gov/ .

Next up: ' The Atmosphere: Getting a Handle on Carbon Dioxide'

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107 Atmosphere Essay Topic Ideas & Examples

Inside This Article

The atmosphere is a critical component of our planet, playing a crucial role in sustaining life and shaping the climate. Understanding the atmosphere and its various aspects is essential for addressing environmental issues, climate change, and even predicting weather patterns. If you are looking for essay topics related to the atmosphere, here are 107 ideas and examples to inspire you:

• The impact of air pollution on human health.
• The role of the atmosphere in climate change.
• The importance of the ozone layer in protecting life on Earth.
• Exploring the causes and consequences of global warming.
• The impact of greenhouse gases on the atmosphere.
• The role of aerosols in climate regulation.
• Analyzing the effects of deforestation on the atmosphere.
• The relationship between urbanization and air quality.
• The influence of industrial emissions on atmospheric composition.
• Investigating the effects of acid rain on ecosystems.
• The role of atmospheric pressure in weather patterns.
• The impact of El Niño and La Niña on global weather patterns.
• Analyzing the connection between air pollution and respiratory diseases.
• The role of the atmosphere in the water cycle.
• The influence of atmospheric circulation on regional climates.
• The impact of air pollution on wildlife and ecosystems.
• The role of atmospheric pollutants in climate feedback loops.
• Investigating the link between air pollution and cardiovascular diseases.
• The effects of volcanic eruptions on the atmosphere.
• The relationship between air pollution and climate refugees.
• Analyzing the impact of aircraft emissions on the atmosphere.
• The role of atmospheric stability in severe weather events.
• The influence of atmospheric moisture on precipitation patterns.
• The effects of atmospheric pollution on agricultural productivity.
• Investigating the connection between air pollution and cognitive function.
• The role of atmospheric composition in determining atmospheric layers.
• Analyzing the impact of wildfires on atmospheric pollution.
• The relationship between air pollution and climate justice.
• The effects of atmospheric pollution on coral reefs and marine life.
• The influence of atmospheric circulation on air quality.
• Investigating the connection between air pollution and childhood development.
• The role of atmospheric pressure in aviation.
• Analyzing the impact of atmospheric pollutants on cultural heritage sites.
• The relationship between air pollution and social inequality.
• The effects of atmospheric pollutants on the ozone layer.
• The influence of atmospheric temperature on agricultural practices.
• Investigating the connection between air pollution and cognitive decline in the elderly.
• The role of atmospheric dynamics in extreme weather events.
• Analyzing the impact of atmospheric pollutants on indoor air quality.
• The relationship between air pollution and allergies.
• The effects of atmospheric pollution on solar energy generation.
• The influence of atmospheric pressure on human physiology.
• Investigating the connection between air pollution and mental health.
• The role of atmospheric aerosols in cloud formation.
• Analyzing the impact of atmospheric pollutants on the Arctic ecosystem.
• The relationship between air pollution and pregnancy outcomes.
• The effects of atmospheric pollution on the visibility in national parks.
• The influence of atmospheric composition on satellite communication.
• Investigating the connection between air pollution and sleep quality.
• The role of atmospheric stability in tornado formation.
• Analyzing the impact of atmospheric pollutants on honeybee populations.
• The relationship between air pollution and skin health.
• The effects of atmospheric pollution on historical artifacts.
• The influence of atmospheric pressure on athletic performance.
• Investigating the connection between air pollution and neurodevelopmental disorders in children.
• The role of atmospheric dynamics in hurricane formation.
• Analyzing the impact of atmospheric pollutants on bird migration patterns.
• The relationship between air pollution and lung cancer.
• The effects of atmospheric pollution on renewable energy technologies.
• The influence of atmospheric temperature on insect populations.
• Investigating the connection between air pollution and workplace productivity.
• The role of atmospheric aerosols in climate engineering.
• Analyzing the impact of atmospheric pollutants on freshwater ecosystems.
• The relationship between air pollution and obesity.
• The effects of atmospheric pollution on historical monuments.
• The influence of atmospheric pressure on scuba diving.
• Investigating the connection between air pollution and fertility rates.
• The role of atmospheric stability in thunderstorm development.
• Analyzing the impact of atmospheric pollutants on pollinators.
• The relationship between air pollution and respiratory allergies.
• The effects of atmospheric pollution on solar radiation reaching the Earth's surface.
• The influence of atmospheric temperature on insect-borne diseases.
• Investigating the connection between air pollution and workplace absenteeism.
• The role of atmospheric aerosols in air quality monitoring.
• Analyzing the impact of atmospheric pollutants on amphibian populations.
• The relationship between air pollution and premature mortality.
• The effects of atmospheric pollution on historical paintings.
• The influence of atmospheric pressure on space exploration.
• Investigating the connection between air pollution and birth outcomes.
• The role of atmospheric stability in hailstorm formation.
• Analyzing the impact of atmospheric pollutants on soil quality.
• The relationship between air pollution and asthma.
• The effects of atmospheric pollution on wind energy generation.
• The influence of atmospheric temperature on mosquito-borne diseases.
• Investigating the connection between air pollution and workplace satisfaction.
• The role of atmospheric aerosols in climate modeling.
• Analyzing the impact of atmospheric pollutants on fish populations.
• The relationship between air pollution and cardiovascular mortality.
• The effects of atmospheric pollution on archaeological sites.
• The influence of atmospheric pressure on weather forecasting.
• Investigating the connection between air pollution and mental well-being.
• The role of atmospheric stability in cyclone formation.
• Analyzing the impact of atmospheric pollutants on bee populations.
• The relationship between air pollution and allergies in children.
• The effects of atmospheric pollution on wind erosion.
• The influence of atmospheric temperature on crop yields.
• Investigating the connection between air pollution and workplace performance.
• The role of atmospheric aerosols in cloud seeding.
• Analyzing the impact of atmospheric pollutants on forest ecosystems.
• The relationship between air pollution and respiratory infections.
• The effects of atmospheric pollution on offshore wind farms.
• The influence of atmospheric pressure on aviation safety.
• Investigating the connection between air pollution and cognitive abilities in children.
• The role of atmospheric stability in monsoon formation.
• Analyzing the impact of atmospheric pollutants on butterfly populations.
• The relationship between air pollution and chronic obstructive pulmonary disease (COPD).
• The effects of atmospheric pollution on wind patterns.

These essay topic ideas offer a wide range of opportunities to explore and understand the various aspects of the atmosphere. Whether you are interested in climate change, air pollution, or the impact of atmospheric phenomena on human health, there is a topic that will spark your curiosity and drive your research forward. Remember to approach these topics with a critical and scientific mindset, utilizing credible sources and evidence to support your arguments.

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10.1: Introduction to the Atmosphere

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Learning Objectives

The goals and objectives of this chapter are to:

• Understand the significance of the atmosphere.
• Describe the composition of the atmospheric gasses.
• Explain the major layers of the atmosphere and their importance.
• Analyze the relationships between energy, temperature, and heat.
• Describe how the Sun influences seasonality.
• Describe how heat is transferred around the planet.
• Dynamic Earth: Introduction to Physical Geography. Authored by : R. Adam Dastrup. Located at : http://www.opengeography.org/physical-geography.html . Project : Open Geography Education. License : CC BY-SA: Attribution-ShareAlike

One of the main components of Earth’s interdependent physical systems is the atmosphere. An atmosphere is made of the layers of gases surrounding a planet or other celestial body. Earth’s atmosphere is composed of about 78% nitrogen, 21% oxygen, and one percent other gases. These gases are found in atmospheric layers (troposphere, stratosphere, mesosphere, thermosphere, and exosphere) defined by unique features such as temperature and pressure. The atmosphere protects life on earth by shielding it from incoming ultraviolet (UV) radiation, keeping the planet warm through insulation, and preventing extremes between day and night temperatures. The sun heats layers of the atmosphere causing it to convect driving air movement and weather patterns around the world.

Biology, Earth Science, Geology, Geography, Physical Geography

Parts of the Atmosphere

We live at the bottom of an invisible ocean called the atmosphere, a layer of gases surrounding our planet. Nitrogen and oxygen account for 99 percent of the gases in dry air, with argon, carbon dioxide, helium, neon, and other gases making up minute portions.

Chemistry, Earth Science, Astronomy, Meteorology, Geography, Physical Geography

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We live at the bottom of an invisible ocean called the atmosphere , a layer of gases surrounding our planet . Nitrogen and oxygen account for 99 percent of the gases in dry air , with argon , carbon dioxide , helium , neon , and other gases making up minute port ions . Water vapor and dust are also part of Earth ’s atmosphere . Other planets and moons have very different atmospheres , and some have no atmospheres at all.

The atmosphere is so spread out that we barely not ice it, yet its weight is equal to a layer of water more than 10 meters (34 feet) deep covering the entire planet. The bottom 30 kilometers (19 miles) of the atmosphere contains about 98 percent of its mass . The atmosphere— air —is much thinner at high altitudes . There is no atmosphere in space. Scientists say many of the gases in our atmosphere were ejected into the air by early volcanoes . At that time, there would have been little or no free oxygen surrounding Earth. Free oxygen consists of oxygen molecules not attached to another element , like carbon (to form carbon dioxide) or hydrogen (to form water). Free oxygen may have been added to the atmosphere by primitive organisms, probably bacteria , during photosynthesis . Photosynthesis is the process a plant or other autotroph uses to make food and oxygen from carbon dioxide and water. Later, more complex forms of plant life added more oxygen to the atmosphere. The oxygen in today’s atmosphere probably took millions of years to accumulate . The atmosphere acts as a gigantic filter , keeping out most ultraviolet radiation while letting in the sun’s warming rays. Ultraviolet radiation is harmful to living things, and is what causes sunburns. Solar heat, on the other hand, is necessary for all life on Earth. Earth’s atmosphere has a layered structure. From the ground toward the sky, the layers are the troposphere , stratosphere , mesosphere , thermosphere , and exosphere . Another layer, called the ionosphere , extends from the mesosphere to the exosphere. Beyond the exosphere is outer space . The boundaries between atmospheric layers are not clearly defined, and change depending on latitude and season . Troposphere The troposphere is the lowest atmospheric layer. On average, the troposphere extends from the ground to about 10 kilometers (six miles) high, ranging from about six kilometers (four miles) at the poles to more than 16 kilometers (10 miles) at the Equator . The top of the troposphere is higher in summer than in winter. Almost all weather develops in the troposphere because it contains almost all of the atmosphere’s water vapor. Clouds , from low-lying fog to thunderheads to high-altitude cirrus , form in the troposphere. Air masses , areas of high-pressure and low-pressure systems , are moved by winds in the troposphere. These weather systems lead to daily weather changes as well as seasonal weather patterns and climate systems, such as El Niño. Air in the troposphere thins as altitude increases. There are fewer molecules of oxygen at the top of Mount Everest , Nepal, for example, than there are on a beach in Hawai'i. This is why mountaineers often use canisters of oxygen when climbing tall peaks. Thin air is also why helicopters have difficulty maneuvering at high altitudes. In fact, a helicopter was not able to land on Mount Everest until 2005. As air in the troposphere thins, temperature decreases. This is why mountaintops are usually much colder than the valleys beneath. Scientists used to think temperature continued to drop as altitude increased beyond the troposphere. But data collected with weather balloons and rockets have showed this is not the case. In the lower stratosphere, temperature stays almost constant. As altitude increases in the stratosphere, temperature actually increases. Solar heat penetrates the troposphere easily. This layer also absorbs heat that is reflected back from the ground in a process called the greenhouse effect . The greenhouse effect is necessary for life on Earth. The atmosphere’s most abundant greenhouse gases are carbon dioxide, water vapor, and methane . Fast-moving, high-altitude winds called jet streams swirl around the planet near the upper boundary of the troposphere. Jet streams are extremely important to the airline industry. Aircraft save time and money by flying in jet streams instead of the lower troposphere, where air is thicker.

Stratosphere The troposphere tends to change suddenly and violently, but the stratosphere is calm. The stratosphere extends from the tropopause , the upper boundary of the troposphere, to about 50 kilometers (32 miles) above Earth’s surface. Strong horizontal winds blow in the stratosphere, but there is little turbulence . This is ideal for planes that can fly in this part of the atmosphere. The stratosphere is very dry and clouds are rare. Those that do form are thin and wispy. They are called nacreous clouds. Sometimes they are called mother-of-pearl clouds because their colors look like those inside a mollusk shell. The stratosphere is crucial to life on Earth because it contains small amounts of ozone , a form of oxygen that prevents harmful UV rays from reaching Earth. The region within the stratosphere where this thin shell of ozone is found is called the ozone layer . The stratosphere’s ozone layer is uneven, and thinner near the poles. The amount of ozone in the Earth’s atmosphere is declining steadily. Scientists have linked use of chemicals such as chlorofluorocarbons (CFCs) to ozone depletion . Mesosphere The mesosphere extends from the stratopause (the upper boundary of the stratosphere) to about 85 kilometers (53 miles) above the surface of the Earth. Here, temperatures again begin to fall. The mesosphere has the coldest temperatures in the atmosphere, dipping as low as -120 degrees Celsius (-184 degrees Fahrenheit or 153 kelvin). The mesosphere also has the atmosphere’s highest clouds. In clear weather, you can sometimes see them as silvery wisps immediately after sunset. They are called noctilucent clouds, or night-shining clouds. The mesosphere is so cold that noctilucent clouds are actually frozen water vapor—ice clouds. Shooting stars —the fiery burnout of meteors , dust, and rocks from outer space—are visible in the mesosphere. Most shooting stars are the size of a grain of sand and burn up before entering the stratosphere or troposphere. However, some meteors are the size of pebbles or even boulders . Their outer layers burn as they race through the mesosphere, but they are massive enough to fall through the lower atmosphere and crash to Earth as meteorites . The mesosphere is the least-understood part of Earth’s atmosphere. It is too high for aircraft or weather balloons to operate, but too low for spacecraft . Sounding rockets have provided meteorologists and astronomers their only significant data on this important part of the atmosphere. Sounding rockets are unmanned research instruments that collect data during suborbital flights. Perhaps because the mesosphere is so little understood, it is home to two meteorological mysteries: sprites and elves . Sprites are reddish, vertical electrical discharges that appear high above thunderheads, in the upper stratosphere and mesosphere. Elves are dim, halo-shaped discharges that appear even higher in the mesosphere. Ionosphere The ionosphere extends from the top half of the mesosphere all the way to the exosphere. This atmospheric layer conducts electricity . The ionosphere is named for ions created by energetic particles from sunlight and outer space. Ions are atoms in which the number of electrons does not equal the number of protons , giving the atom a positive (fewer electrons than protons) or negative (more electrons than protons) charge. Ions are created as powerful x-rays and UV rays knock electrons off atoms. The ionosphere—a layer of free electrons and ions—reflects radio waves . Guglielmo Marconi , the “Father of Wireless,” helped prove this in 1901 when he sent a radio signal from Cornwall, England, to St. John’s, Newfoundland, Canada. Marconi’s experiment demonstrated that radio signals did not travel in a straight line, but bounced off an atmospheric layer—the ionosphere. The ionosphere is broken into distinct layers, called the D, E, F1, and F2 layers. Like all other parts of the atmosphere, these layers vary with season and latitude. Changes in the ionosphere actually happen on a daily basis. The low D layer, which absorbs high-frequency radio waves, and the E layer actually disappear at night, which means radio waves can reach higher into the ionosphere. That’s why AM radio stations can extend their range by hundreds of kilometers every night. The ionosphere also reflects particles from solar wind , the stream of highly charged particles ejected by the sun. These electrical displays create auroras (light displays) called the Northern and Southern Lights . Thermosphere The thermosphere is the thickest layer in the atmosphere. Only the lightest gases—mostly oxygen, helium, and hydrogen—are found here. The thermosphere extends from the mesopause (the upper boundary of the mesosphere) to 690 kilometers (429 miles) above the surface of the Earth. Here, thinly scattered molecules of gas absorb x-rays and ultraviolet radiation. This absorption process propels the molecules in the thermosphere to great speeds and high temperatures. Temperatures in the thermosphere can rise to 1,500 degrees Celsius (2,732 degrees Fahrenheit or 1,773 kelvin). Though the temperature is very high, there is not much heat. How is that possible? Heat is created when molecules get excited and transfer energy from one molecule to another. Heat happens in an area of high pressure (think of water boiling in a pot). Since there is very little pressure in the thermosphere, there is little heat transfer. The Hubble Space Telescope and the International Space Station (ISS) orbit Earth in the thermosphere. Even though the thermosphere is the second-highest layer of Earth’s atmosphere, satellites that operate here are in “ low-Earth orbit .” Exosphere The fluctuating area between the thermosphere and the exosphere is called the turbopause . The lowest level of the exosphere is called the exobase . At the upper boundary of the exosphere, the ionosphere merges with interplanetary space , or the space between planets. The exosphere expands and contracts as it comes into contact with solar storms . In solar storms particles are flung through space from explosive events on the sun, such as solar flares and coronal mass ejections (CMEs). Solar storms can squeeze the exosphere to just 1,000 kilometers (620 miles) above the Earth. When the sun is calm, the exosphere can extend 10,000 kilometers (6,214 miles). Hydrogen, the lightest element in the universe , dominates the thin atmosphere of the exosphere. Only trace amounts of helium, carbon dioxide, oxygen, and other gases are present. Many weather satellites orbit Earth in the exosphere. The lower part of the exosphere includes low-Earth orbit, while medium-Earth orbit is higher in the atmosphere. The upper boundary of the exosphere is visible in satellite images of Earth. Called the geocorona , it is the fuzzy blue illumination that circles the Earth. Extraterrestrial Atmospheres All the planets in our solar system have atmospheres. Most of these atmospheres are radically different from Earth’s, although they contain many of the same elements. The solar system has two major types of planets: terrestrial planets (Mercury, Venus, Earth, and Mars) and gas giants (Jupiter, Saturn, Uranus, and Neptune). The atmospheres of the terrestrial planets are somewhat similar to Earth’s. Mercury’s atmosphere contains only a thin exosphere dominated by hydrogen, helium, and oxygen. Venus’ atmosphere is much thicker than Earth’s, preventing a clear view of the planet. Its atmosphere is dominated by carbon dioxide, and features swirling clouds of sulfuric acid . The atmosphere on Mars is also dominated by carbon dioxide, although unlike Venus, it is quite thin. Gas giants are composed of gases. Their atmospheres are almost entirely hydrogen and helium. The presence of methane in the atmospheres of Uranus and Neptune give the planets their bright blue color. In the lower atmospheres of Jupiter and Saturn, clouds of water, ammonia , and hydrogen sulfide form clear bands. Fast winds separate light-colored bands, called zones, from dark-colored bands, called belts . Other weather phenomena , such as cyclones and lightning , create patterns in the zones and belts. Jupiter’s Great Red Spot is a centuries-old cyclone that is the largest storm in the solar system. The moons of some planets have their own atmospheres. Saturn’s largest moon, Titan , has a thick atmosphere made mostly of nitrogen and methane. The way sunlight breaks up methane in Titan’s ionosphere helps give the moon an orange color. Most celestial bodies, including all the asteroids in the asteroid belt and our own moon, do not have atmospheres. The lack of an atmosphere on the Moon means it does not experience weather. With no wind or water to erode them, many craters on the Moon have been there for hundreds and even thousands of years. The way a celestial body ’s atmosphere is structured and what it’s made of allow astrobiologists to speculate what kind of life the planet or moon may be able to support. Atmospheres, then, are important markers in space exploration. A planet or moon’s atmosphere must contain specific chemicals to support life as we know it. These chemicals include hydrogen, oxygen, nitrogen, and carbon. Although Venus, Mars, and Titan have similar atmospheric gases, there is nowhere in the solar system besides Earth with an atmosphere able to support life. Venus’ atmosphere is far too thick, Mars’ far too thin, and Titan’s far too cold.

Ingredients for Life Scientists have gathered enough information about other planets in our solar system to know that none can support life as we know it. Life is not possible without a stable atmosphere containing the right chemical ingredients for living organisms: hydrogen, oxygen, nitrogen, and carbon. These ingredients must be balanced—not too thick or too thin. Life also depends on the presence of water. Jupiter, Saturn, Uranus, and Neptune all have atmospheres made mostly of hydrogen and helium. These planets are called gas giants, because they are mostly made of gas and do not have a solid outer crust. Mercury and Mars have some of the right ingredients, but their atmospheres are far too thin to support life. The atmosphere of Venus is too thick—the planet's surface temperature is more than 460 degrees Celsius (860 degrees Fahrenheit). Jupiter's moon Europa has a thin atmosphere rich with oxygen. It is likely covered by a huge ocean of liquid water. Some astrobiologists think that if life exists elsewhere in the solar system, it will be near vents at the bottom of Europa's ocean.

Magnetosphere Earths magnetosphere is not considered part of the atmosphere. The magnetosphere, formed by the Earths magnetic fields, protects the atmosphere by preventing it from being blown away by powerful solar wind.

Atmospheric Orbit Although the International Space Station orbits in the thermosphere, most satellites orbit the Earth outside its atmosphere. GPS satellites, for instance, are in orbit more than 20,000 kilometers (12,400 miles) above the Earth.

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Composition and Structure of the Atmosphere

Atmosphere refers to the layer of gases that surrounds Earth and is held in place by Earth’s gravitational attraction (gravity). The mix of gases in the atmosphere forms a complex system organized into layers that together support life on Earth. Although there are numerous gases, as shown in Table 6.1, the top four gases make up 99.998 % of the volume of clean dry air (unpolluted air that does not contain water vapor). Of this dry composition of the atmosphere nitrogen, by far, is the most common (78%). Nitrogen dilutes oxygen and prevents rapid or instantaneous burning at the Earth’s surface, as oxygen gas is a necessary reactant of the combustion process. Nitrogen is also needed and used by living things to make proteins, though as nitrogen gas, N 2 , it is unavailable to most living things. Oxygen is used by all living things to make molecules that are essential for life. It is also essential for aerobic respiration as well as combustion or burning. Argon is a non-reactive gas and we use it in light bulbs, in double-pane windows, and to preserve priceless documents such as the original Declaration of Independence and the Constitution. Carbon dioxide is an essential gas used by plants and other organisms to make sugar (food) through photosynthesis. This process is essential for other life as well because during photosynthesis, water molecules are split apart and their oxygen is released back to the atmosphere. Carbon dioxide also acts as a blanket that prevents the escape of heat into outer space (see more on this in Chapter 7). The atmosphere is rarely, if ever, completely dry. Water vapor (water in a ‘gas’ state) is usually present up to about 4% of the total volume depending on location. In the Earth’s desert regions (30° N/S) when dry winds are blowing, the water vapor contribution to the composition of the atmosphere will be near zero.

Table 6.1: Average composition of clean dry air in the lower atmosphere

Source: National Weather Service http://www.srh.noaa.gov/jetstream/atmos/atmos intro.htm

Earth’s atmosphere is divided into four distinct layers based on thermal characteristics (temperature changes), chemical composition, movement, and density (Figure 6.1). The troposphere is the lowest layer extending from the surface up to roughly 18 km above the surface depending on location (varies from as low as 6 km to as high as 20 km). There is a continuous flow and swirling of air constantly through convection currents redistributing heat and moisture around the globe. This results in the short-lived and local patterns of temperature and moisture that we call weather. Because gravity holds most air molecules close to the Earth’s surface, the troposphere is the densest of all layers, containing about 75% of the total mass of the atmosphere. The density of the gases in this layer decreases with height so the air becomes thinner. In response, the temperature in the troposphere also decreases with height. As one climbs higher, the temperature drops from an average of around 17°C (62°F) at sea level to about -51°C (-60°F) at the tropopause, a sharp boundary at the top of the troposphere that limits mixing between the troposphere and the upper layers.

The stratosphere is the layer that extends from the tropopause up to about 50 km to 53 km above the Earth’s surface depending on location. The proportions of most gases in this layer are similar to that of the troposphere with two main exceptions: 1) there is almost no water vapor in the stratosphere and 2) the stratosphere has nearly 1,000 times more ozone (O 3 ) than the troposphere. With only about 19% of the total mass of the atmosphere, the density of the stratosphere is significantly lower than the troposphere. However, the temperature in this region increases with height as a result of heat that is produced during the formation of ozone (more on ozone in section 6.2). This heat is responsible for temperature increases from an average of -51 °C (-60°F) at tropopause to a maximum of about -15°C (5°F) at the top of the stratosphere. This increase in temperature with height means warmer air is located above cooler air. This prevents “convection” as there is no upward vertical movement of the gases. The consequence of this little to no mixing of gases in the stratosphere makes it relatively calm but also means that once substances such as pollutants enter this zone, they can remain suspended for many years. The top of the stratosphere is bound by a boundary known as the stratopause.

Above the stratosphere is the mesosphere which extends to about 85 km above the Earth’s surface. The mesosphere has no ozone molecules and the other gases such as oxygen and nitrogen continue to become less dense with height. As a result, not much ultraviolet and x-ray radiation from the sun is absorbed by molecules in this layer, so temperature decreases with altitude. Both the stratosphere and the mesosphere are considered the middle atmosphere.

Between about 85 km and 600 km lies the thermosphere. This layer is known as the upper atmosphere. Unlike the mesosphere, the gases in this layer readily absorb incoming high-energy ultraviolet and x-ray radiation from the sun. Because of this absorption, the temperature in the thermosphere increases with height and can reach as high as 2,000°C (3,600°F) near the top depending on solar activity. However, despite the high temperature, this layer of the atmosphere would still feel very cold to our skin due to the very thin atmosphere. The high temperature indicates the amount of energy absorbed by molecules but with so few in this layer, the total number of molecules is not enough to heat our skin. There’s no sharp boundary that marks the end of the atmosphere. Pressure and density simply continue to decrease with distance until they become indistinguishable from the near-vacuum of outer space.

Attribution

Zehnder, Caralyn; Manoylov, Kalina; Mutiti, Samuel; Mutiti, Christine; VandeVoort, Allison; and Bennett, Donna, “Introduction to Environmental Science: 2nd Edition” (2018). Biological Sciences Open Textbooks. 4. https://oer.galileo.usg.edu/biology-textbooks/4 This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License .

Environmental Biology Copyright © by Various Authors is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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AP®︎/College Environmental science

Course: ap®︎/college environmental science   >   unit 3, earth's atmosphere.

• Global wind patterns
• Earth's air and water
• Earth is surrounded by a mixture of gases called the atmosphere . The composition of the atmosphere is 78 % ‍   nitrogen and 21 % ‍   oxygen, with the remaining 1 % ‍   consisting of water vapor, argon, carbon dioxide, and small amounts of other gases.
• Troposphere : The troposphere is the layer closest to Earth. It is the densest layer (i.e., contains the most air particles), and is where most of Earth’s weather and cloud formation occurs. The troposphere is heated primarily by energy from the sun radiating off the Earth’s surface. This, along with the decrease in pressure that occurs with altitude, means that the troposphere has a temperature gradient that decreases with altitude.
• Stratosphere : The stratosphere is the layer above the troposphere. It has a concentrated region of ozone gas called the ozone layer , which keeps about 95 % ‍   of the sun's harmful UV radiation from reaching the Earth’s surface. Ozone molecules absorb UV radiation and release heat, which causes the stratosphere to have a temperature gradient that increases with altitude.
• Mesosphere : The mesosphere is the layer above the stratosphere. The mesosphere is heated primarily by the stratosphere below, so it has a temperature gradient that decreases with altitude. The mesosphere is one of the coldest places on Earth. The average temperature is around minus 85 ° ‍   C ( − 120 ° ‍   F)!
• Thermosphere : The thermosphere is the layer above the mesosphere. It has a very low density of gas molecules. These molecules absorb highly energetic radiation from the sun, so the thermosphere has a temperature gradient that increases with altitude.
• Exosphere : The exosphere is the highest layer of Earth’s atmosphere, where there is an extremely low density of gas molecules. These molecules often escape into space.

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Earth's Atmosphere

What is earth’s atmosphere, a jacket for the planet.

Earth is a great planet to live on because it has a wonderful atmosphere around it. This jacket of gases does a lot for us. It keeps us warm, it gives us oxygen to breathe, and it’s where our weather happens.

The atmosphere surrounds our planet like the peel of an orange. But it’s not the same everywhere. It has different layers with different qualities.

One atmosphere, many layers

Earth’s atmosphere has six different layers. They go from the ground all the way to outer space. To learn more about each layer of the atmosphere, click the images below.

(This is only part of the exosphere. It's actually 12 times bigger than this!)

If you liked this, you may like:.

The Atmosphere

Introduction to the atmosphere, learning objectives.

The goals and objectives of this chapter are to:

• Understand the significance of the atmosphere.
• Describe the composition of the atmospheric gasses.
• Explain the major layers of the atmosphere and their importance.
• Analyze the relationships between energy, temperature, and heat.
• Describe how the Sun influences seasonality.
• Describe how heat is transferred around the planet.
• Dynamic Earth: Introduction to Physical Geography. Authored by : R. Adam Dastrup. Located at : http://www.opengeography.org/physical-geography.html . Project : Open Geography Education. License : CC BY-SA: Attribution-ShareAlike

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4 (page 65) p. 65 Atmospheric composition

• Published: March 2017
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Nitrogen, oxygen, and argon represent more than 99.9% of the air we breathe. But Earth’s atmosphere hasn’t always had that composition—it is on at least its third distinctive atmosphere. ‘Atmospheric composition’ provides a brief history of Earth’s atmosphere, before considering the two most important regions of the atmosphere for human survival—the stratosphere and troposphere. The stratospheric ozone layer shields harmful ultraviolet-B light penetrating to the surface, thereby protecting humans and ecosystems from harmful ultraviolet radiation. The troposphere is where billions of people live and breathe. It is also where air pollutants are emitted, wildfires burn, vegetation grows, and where the oceans exchange gases. The impact of atmospheric aerosols and greenhouse gases is also discussed.

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Layers of Earth's Atmosphere

Earth's atmosphere is composed of a series of layers, each with its own specific traits. Moving upward from ground level, these layers are called the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The exosphere gradually fades away into the realm of interplanetary space.

The layers of the atmosphere: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

• Troposphere

The troposphere is the lowest layer of our atmosphere. Starting at ground level, it extends upward to about 10 km (6.2 miles or about 33,000 feet) above sea level. We humans live in the troposphere, and nearly all weather occurs in this lowest layer. Most clouds appear here, mainly because 99% of the water vapor in the atmosphere is found in the troposphere. Air pressure drops, and temperatures get colder, as you climb higher in the troposphere .

• Stratosphere

The next layer up is called the stratosphere . The stratosphere extends from the top of the troposphere to about 50 km (31 miles) above the ground. The infamous ozone layer is found within the stratosphere. Ozone molecules in this layer absorb high-energy ultraviolet (UV) light from the Sun, converting the UV energy into heat. Unlike the troposphere, the stratosphere actually gets warmer the higher you go! That trend of rising temperatures with altitude means that air in the stratosphere lacks the turbulence and updrafts of the troposphere beneath. Commercial passenger jets fly in the lower stratosphere, partly because this less-turbulent layer provides a smoother ride. The jet stream flows near the border between the troposphere and the stratosphere.

Above the stratosphere is the mesosphere . It extends upward to a height of about 85 km (53 miles) above our planet. Most meteors burn up in the mesosphere. Unlike the stratosphere, temperatures once again grow colder as you rise up through the mesosphere. The coldest temperatures in Earth's atmosphere, about -90° C (-130° F), are found near the top of this layer. The air in the mesosphere is far too thin to breathe (the air pressure at the bottom of the layer is well below 1% of the pressure at sea level and continues dropping as you go higher).

• Thermosphere

The layer of very rare air above the mesosphere is called the thermosphere . High-energy X-rays and UV radiation from the Sun are absorbed in the thermosphere, raising its temperature to hundreds or at times thousands of degrees. However, the air in this layer is so thin that it would feel freezing cold to us! In many ways, the thermosphere is more like outer space than a part of the atmosphere. In fact, the approximate boundary between our atmosphere and outer space, known as the Kármán Line, is in the thermosphere, at an altitude of about 100 km. Many satellites actually orbit Earth within the thermosphere! Variations in the amount of energy coming from the Sun exert a powerful influence on both the height of the top of this layer and the temperature within it. Because of this, the top of the thermosphere can be found anywhere between 500 and 1,000 km (311 to 621 miles) above the ground. Temperatures in the upper thermosphere can range from about 500° C (932° F) to 2,000° C (3,632° F) or higher.

Although some experts consider the thermosphere to be the uppermost layer of our atmosphere, others consider the exosphere to be the actual "final frontier" of Earth's gaseous envelope. As you might imagine, the "air" in the exosphere is very, very, very thin, making this layer even more space-like than the thermosphere. In fact, the air in the exosphere is constantly - though very gradually - "leaking" out of Earth's atmosphere into outer space. There is no clear-cut upper boundary where the exosphere finally fades away into space. Different definitions place the top of the exosphere somewhere between 100,000 km (62,000 miles) and 190,000 km (120,000 miles) above the surface of Earth. The latter value is about halfway to the Moon!

The ionosphere is not a distinct layer like the others mentioned above. Instead, the ionosphere is a series of regions in parts of the mesosphere and thermosphere where high-energy radiation from the Sun has knocked electrons loose from their parent atoms and molecules. The electrically charged atoms and molecules that are formed in this way are called ions, giving the ionosphere its name and endowing this region with some special properties. The aurora, or Northern Lights and Southern Lights, occur in the parts of the thermosphere that correspond to layers of the ionosphere.

• Earth's Atmosphere (overview)

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Israel-Hamas war

Trump hush money trial

Second day of testimony wraps in Trump hush money trial

From CNN's Jeremy Herb, Lauren del Valle and Kara Scannell in the courthouse

Key takeaways from Tuesday's hush money trial against Donald Trump

From CNN's Jeremy Herb, Lauren del Valle and Kara Scannell

Donald Trump had a frustrating day in court on Tuesday. Even with an abbreviated day for the Passover holiday, there was a one-two punch of a morning hearing about possible gag order violations and the testimony about the “catch-and-kill” deals to bury negative stories about the former president during the 2016 election.

Former tabloid publisher David Pecker will return to the stand on Thursday after court is dark on Wednesday. He has spoken now about two of the three catch-and-kill deals — but not adult film star Stormy Daniels, which is likely coming on Thursday.

Here are key takeaways from Tuesday’s day in court:

• Gag order hearing goes badly for Trump: Judge Juan Merchan issued the gag order before the trial began, limiting Trump from publicly discussing witnesses, the jury, the district attorney’s staff and Merchan's family. He has not yet ruled on the district attorney’s motion to sanction Trump for allegedly violating the order, but it wasn’t hard to tell the judge’s sentiments. Merchan rejected the explanations that Trump attorney Todd Blanche offered for the offending posts after Trump’s attorney tried to argue that posts about Stormy Daniels and Michael Cohen were political and not about the case.
• Judge says Trump lawyers are "losing all credibility": Tensions continued to grow between Trump’s legal team and the trial judge during the gag order hearing. Merchan repeatedly asked Blanche to clarify examples of when Trump was specifically responding to attacks from Cohen and Daniels on social media and grew visibly frustrated when Blanche failed to comply. Last week, Merchan supported prosecutors when they refused to give Trump’s legal team notice of their witness list, saying he understood the sentiment given Trump’s social media attacks.
• Pecker puts jury inside how AMI helped Trump in 2016 campaign: Pecker, who ran American Media Inc. during the 2016 election, testified for around two-and-a-half hours on Tuesday, walking jurors through how he worked with Cohen on Trump’s behalf to squash unflattering stories during the 2016 election. He testified about the “catch and kill” deals involving McDougal and Trump’s doorman. He said that he met with Trump and Cohen in 2015 where he agreed to be the “eyes and ears” of the campaign and look out for negative stories.
• Pecker places Michael Cohen deep in the conspiracy: Pecker placed Cohen in the heart   of the alleged “catch and kill conspiracy” by testifying that Cohen was the go-between for Trump fielding media stories from Pecker since 2007. At the August 2015 Trump Tower meeting, Pecker said he would notify Cohen about negative stories. During Trump’s campaign in 2015 and 2016, Pecker said Cohen would also pitch stories about Trump’s political opponents and offer feedback on behalf of “the boss,” as Cohen referred to Trump.

Secret Service and other officials discussing what to do if Trump is jailed for contempt of court, sources say

From CNN's John Miller

The US Secret Service, court officers and even the New York City Department of Corrections have been quietly discussing what to do if former President Donald Trump ends up being jailed for contempt of court, officials familiar with the plans tell CNN.

In Trump’s civil trial , Judge Arthur Engoran held the former president in contempt a number of times for violating his orders – but imposed only monetary penalties. In Trump’s civil trial in federal courts in January, Judge Lewis Kaplan considered holding Trump in contempt of court. He strongly hinted that he would order the former president to be held in custody if there was another violation of his instructions.

While that didn’t happen, it did cause a stir within the Secret Service and the US Marshals Service as they had to figure out how they would handle logistics if the judge did put Trump in custody, the sources said. Agents scrambled to find an office or conference room for this purpose if they needed to.

In the hush money case, an assistant district attorney asked Judge Juan Merchan to consider jail time for Trump’s alleged acts of contempt. Since last week, Secret Service agents, court officers and NYPD detectives assigned to Trump's security detail have been discussing how that would be handled if it came to pass, though nothing was decided.

The one thing that was decided was that this was not a plan that should be made just by the court, the prosecutors and Trump’s lawyers, the sources said.

Instead, the Secret Service would want to be included in any discussions about how and where Trump is being held in custody — if that came to pass — simply because it would have to figure out how to carry out officers' protective obligations. 

Trump falsely claims “thousands” of his supporters were turned away outside of the courtroom

From CNN's Kate Sullivan

Former President Donald Trump falsely claimed on Tuesday that “thousands” of his supporters were “turned away” by police from the courthouse where his New York criminal hush money trial is taking place. 

In the same  Truth Social post , Trump attacked New York Times reporter Maggie Haberman, who wrote about Trump not being happy that only a handful of his supporters had shown up outside of the courthouse. 

Trump has issued public calls on social media for his supporters to show up outside of the courthouse to peacefully protest. 

“Thousands of people were turned away from the Courthouse in Lower Manhattan by steel stanchions and police, literally blocks from the tiny side door from where I enter and leave. It is an armed camp to keep people away. Maggot Hagerman of The Failing New York Times, falsely reported that I was disappointed with the crowds. No, I’m disappointed with Maggot, and her lack of writing skill, and that some of these many police aren’t being sent to Columbia and NYU to keep the schools open and the students safe,” Trump said. 

CNN’s Kaitlan Collins  has reported  that protestors are allowed outside the courthouse, but his supporters have just been small in number.

Pecker testified about a 2015 meeting with Trump. Here's a timeline of key events in the hush money case

From CNN’s Lauren del Valle, Kara Scannell, Annette Choi and Gillian Roberts 

On Tuesday, former American Media Inc. CEO David Pecker  testified about his August 2015 meeting with former President Donald Trump.

Pecker said he agreed to be the “eyes and ears” for Trump’s campaign and flag any negative stories to Trump’s then-fixer Michael Cohen.

CNN compiled a timeline of the key events leading up to the historic trial. Read up on the moments below:

• September 2016: Donald Trump discusses a $150,000 hush money payment understood to be for former Playboy model Karen McDougal with Michael Cohen who secretly records the conversation . McDougal has alleged she had an extramarital affair with Trump beginning in 2006, which he has denied. 
• October 7, 2016: The Washington Post releases an "Access Hollywood" video from 2005 in which Trump uses vulgar language to describe his sexual approach to women with show host Billy Bush. 
• October 27, 2016: According to prosecutors, Cohen pays Stormy Daniels $130,000 through her attorney via a shell company in exchange for her silence about an affair she allegedly had with Trump in 2006. This $130,000 sum is separate from the $150,000 paid to McDougal. Trump has publicly denied having any affairs and has denied making the payments. 
• November 8, 2016: Trump secures the election to become the 45th president of the United States. 
• February 2017: Prosecutors say Cohen meets with Trump in the Oval Office to confirm how he would be reimbursed for the hush money payment Cohen fronted to Daniels. Under the plan, Cohen would send a series of false invoices requesting payment for legal services he performed pursuant to a retainer agreement and receive monthly checks for $35,000 for a total of $420,000 to cover the payment, his taxes and a bonus, prosecutors alleged. Prosecutors also allege there was never a retainer agreement. 
• January 2018: The Wall Street Journal breaks news about the hush money payment Cohen made to Daniels in 2016. 

See the full timeline.  

Fact check: Trump falsely describes gag order restrictions

From CNN's Daniel Dale

Upon leaving the courtroom on Tuesday, former President Donald Trump approached media cameras, began talking, and complained that he is “not allowed to talk.” 

Trump was criticizing Judge Juan Merchan’s gag order on him. Merchan had held a hearing on Tuesday morning to consider prosecutors’ allegations that Trump violated the gag order with a series of  online posts , including some in which the presumptive Republican presidential nominee  shared others’ articles related to the case  on social media.

Trump claimed, “Can’t even allow articles to be put in.” He claimed the articles he is referring to say “the case is a sham." He added, “I don’t even know if you’re allowed to put them in.” He also claimed that although others are permitted to lie and speak about him, “I’m not allowed to say anything.”

“I’d love to talk to you people, I’d love to say everything that’s on my mind, but I’m restricted because I have a gag order," Trump said.

Facts First :  As he  has before , Trump made Merchan’s gag order sound far broader than it is. The  gag order  does not prohibit Trump from declaring the case a sham or from sharing others’ claims that the case is a sham. It also does not prohibit Trump from speaking to the media about the case, from defending his conduct at issue in the case, from denouncing the judge and district attorney involved in the case, or from campaigning for the presidency with speeches, media interviews and online posts. Rather, the gag order forbids Trump from three specific categories of speech:

• Speaking publicly or directing others to speak publicly about known or foreseeable witnesses, specifically about their participation in the case
• Speaking publicly or directing others to speak publicly about prosecutors — other than Manhattan District Attorney Alvin Bragg — including, staff members in Bragg's office and the court, and their family members if those statements are made with the intent to interfere with the case
• Speaking publicly or directing others to speak publicly about jurors or prospective jurors

In his comments on Tuesday, Trump made the point that an article may have a certain headline that generally denounces the case but, “somewhere deep” in the body of the text, may mention somebody’s name he is not permitted to mention because of the gag order. It’s not clear how Merchan would view Trump having shared an article in which, say, a witness’s name was only mentioned deep in the text. To date, though, articles that prosecutors have alleged Trump violated the gag order by sharing  featured headlines  that made it entirely clear the articles discussed likely witness Michael Cohen, Trump’s former lawyer and fixer. 

Catch up on David Pecker's second day of testimony — and the gag order hearing earlier this morning

From CNN staff

Former tabloid executive David Pecker was back on the stand Tuesday to resume his testimony in the hush money trial against former President Donald Trump.

Pecker testified about a myriad of topics — but mainly established the substance of the August 2015 meeting at the crux of the “catch and kill” practice that is central to the case.

As the then-chairman of American Media Inc., which publishes the National Enquirer,  Pecker  was involved in numerous schemes to kill negative stories about Trump, and he allegedly helped broker the deal with Stormy Daniels.

Before Pecker returned to the stand, Judge Juan Merchan held a hearing on whether the former president violated the gag order in the hush money case. Under the order, Trump is barred from publicly discussing witnesses or jurors in the case. Merchan said he is reserving a decision on the gag order violations.

Court is not in session on Wednesday. The trial will resume Thursday morning.

Here are key moments from Pecker's testimony:

• Relationship with Trump: Pecker said he has known Trump since the 80s and has had a “great relationship” with him over the years. He said that as a celebrity, Trump advised him on parties and events to attend and introduced him to various people in New York. The former tabloid executive said he saw Trump more frequently after he announced his 2016 presidential run.
• Meeting at Trump Tower: The former tabloid publisher said he attended a meeting with Trump and Michael Cohen in August 2015 where he told Trump he would be his “eyes and ears.” Pecker said he offered to tell Cohen “about women selling stories” so that Cohen could have those stories killed or for someone to purchase them. The agreements with Trump were not put in writing , Pecker said.
• Negative stories: Pecker said he would contact Cohen directly if he heard any negative stories about Trump or his family. He also testified that Cohen would request the Enquirer run negative stories about Trump’s political opponents. The Enquirer would also send articles to Cohen before they were published, Pecker said.
• Trump’s business practices: Pecker testified that he saw Trump review and sign invoices and checks and described him as “very knowledgable” and almost “a micromanager” in business. He also described Trump as “very frugal” in his approach to money.
• Pecker claims mutual benefit: Pecker testified that publishing negative stories about Trump’s opponents and alerting him about damaging information had a mutual benefit for the Enquirer and the campaign. Prosecutor Joshua Steinglass, though, pushed back and had Pecker confirm that stopping stories from being printed about Trump only benefited the campaign .
• Headlines and documents enter evidence: The jury was shown a series of National Enquirer articles both praising Trump and attacking political opponents . Prosecutors also introduced AMI business records into evidence, including text messages.
• First "catch and kill" story: Pecker said the first time he paid to kill a negative article about Trump was when he bought a story for $30,000 from a doorman who said Trump had fathered a child. Pecker said he decided to buy the story even after knowing it was false "it would have been very embarrassing to the campaign ” and Trump. The doorman was eventually released from the exclusivity agreement in December 2016 — after the election, at Cohen’s request.
• Karen McDougal: Pecker said former National Enquirer editor-in-chief Dylan Howard went to interview former Playboy model Karen McDougal about a story she was trying to sell alleging she had a relationship with Trump, which the former president denies. Pecker testified that Cohen called him frequently to ask about what happened at the interview and was agitated.

Analysis: Trump faces another major legal battle at the Supreme Court on Thursday 

From CNN's Ronald Brownstein

The Supreme Court’s hearing on  former President Donald Trump’s  immunity claim — happening on Thursday — will underline a historic power shift.

In a closely divided era when neither party has proven able to maintain control of the White House and Congress for very long, the six GOP-appointed justices on the high court have become the most durable source of influence determining the nation’s direction.

“There’s an argument to be made that the Supreme Court is the central character in our national story right now because they are setting the terms by which the other branches and the states and the American people operate in a much more assertive way than perhaps they ever have,” said historian Jeff Shesol.

Although Chief Justice John Roberts  at his confirmation hearing famously likened the court to an impartial “umpire, ” the conservative majority has steadily steered policy on a wide range of social, racial and economic issues toward the preferences of the Republican Party, whose presidents nominated them and whose senators provided the vast majority of votes to confirm them.

The rulings by the GOP-appointed justices over roughly the past two decades have produced cumulative policy changes “way more extensive than any administration, even within unified control of government, has been able to generate,” said Paul Pierson, a University of California at Berkeley political scientist.

The Supreme Court arguments will come as Trump sits in New York for his hush money trial proceedings.

Read the full analysis.

Prosecutors zeroed in on witness David Pecker today. These are the other key players in the trial

From CNN's Kaanita Iyer, Amy O'Kruk and Curt Merrill

Donald Trump has been accused of taking part in an illegal conspiracy to undermine the integrity of the 2016 election and an unlawful plan to suppress negative information, which included a hush money payment made to an adult-film star to hide an affair. Trump has denied the affair.

Prosecutors allege that Trump allegedly disguised the transaction as a legal payment and falsified business records numerous times to “promote his candidacy.” Trump faces 34 counts of falsifying business records. He has pleaded not guilty.

David Pecker, the ex-publisher of the National Enquirer, was the prosecution's first witness.

Read up on the other key people in the Trump hush money criminal trial:

See a courtroom sketch from David Pecker's testimony today 

From Christina Cornell

No cameras are allowed inside the Manhattan courtroom where Donald Trump's hush money trial is underway, but sketch artists were capturing the scene as former tabloid executive David Pecker took the stand.

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Guest Essay

What Sentencing Could Look Like if Trump Is Found Guilty

By Norman L. Eisen

Mr. Eisen is the author of “Trying Trump: A Guide to His First Election Interference Criminal Trial.”

For all the attention to and debate over the unfolding trial of Donald Trump in Manhattan, there has been surprisingly little of it paid to a key element: its possible outcome and, specifically, the prospect that a former and potentially future president could be sentenced to prison time.

The case — brought by Alvin Bragg, the Manhattan district attorney, against Mr. Trump — represents the first time in our nation’s history that a former president is a defendant in a criminal trial. As such, it has generated lots of debate about the case’s legal strength and integrity, as well as its potential impact on Mr. Trump’s efforts to win back the White House.

A review of thousands of cases in New York that charged the same felony suggests something striking: If Mr. Trump is found guilty, incarceration is an actual possibility. It’s not certain, of course, but it is plausible.

Jury selection has begun, and it’s not too soon to talk about what the possibility of a sentence, including a prison sentence, would look like for Mr. Trump, for the election and for the country — including what would happen if he is re-elected.

The case focuses on alleged interference in the 2016 election, which consisted of a hush-money payment Michael Cohen, the former president’s fixer at the time, made in 2016 to a porn star, Stormy Daniels, who said she had an affair with Mr. Trump. Mr. Bragg is arguing that the cover-up cheated voters of the chance to fully assess Mr. Trump’s candidacy.

This may be the first criminal trial of a former president in American history, but if convicted, Mr. Trump’s fate is likely to be determined by the same core factors that guide the sentencing of every criminal defendant in New York State Court.

Comparable cases. The first factor is the base line against which judges measure all sentences: how other defendants have been treated for similar offenses. My research encompassed almost 10,000 cases of felony falsifying business records that have been prosecuted across the state of New York since 2015. Over a similar period, the Manhattan D.A. has charged over 400 of these cases . In roughly the first year of Mr. Bragg’s tenure, his team alone filed 166 felony counts for falsifying business records against 34 people or companies.

Contrary to claims that there will be no sentence of incarceration for falsifying business records, when a felony conviction involves serious misconduct, defendants can be sentenced to some prison time. My analysis of the most recent data indicates that approximately one in 10 cases in which the most serious charge at arraignment is falsifying business records in the first degree and in which the court ultimately imposes a sentence, results in a term of imprisonment.

To be clear, these cases generally differ from Mr. Trump’s case in one important respect: They typically involve additional charges besides just falsifying records. That clearly complicates what we might expect if Mr. Trump is convicted.

Nevertheless, there are many previous cases involving falsifying business records along with other charges where the conduct was less serious than is alleged against Mr. Trump and prison time was imposed. For instance, Richard Luthmann was accused of attempting to deceive voters — in his case, impersonating New York political figures on social media in an attempt to influence campaigns. He pleaded guilty to three counts of falsifying business records in the first degree (as well as to other charges). He received a sentence of incarceration on the felony falsification counts (although the sentence was not solely attributable to the plea).

A defendant in another case was accused of stealing in excess of $50,000 from her employer and, like in this case, falsifying one or more invoices as part of the scheme. She was indicted on a single grand larceny charge and ultimately pleaded guilty to one felony count of business record falsification for a false invoice of just under $10,000. She received 364 days in prison.

To be sure, for a typical first-time offender charged only with run-of-the-mill business record falsification, a prison sentence would be unlikely. On the other hand, Mr. Trump is being prosecuted for 34 counts of conduct that might have changed the course of American history.

Seriousness of the crime. Mr. Bragg alleges that Mr. Trump concealed critical information from voters (paying hush money to suppress an extramarital relationship) that could have harmed his campaign, particularly if it came to light after the revelation of another scandal — the “Access Hollywood” tape . If proved, that could be seen not just as unfortunate personal judgment but also, as Justice Juan Merchan has described it, an attempt “to unlawfully influence the 2016 presidential election.”

History and character. To date, Mr. Trump has been unrepentant about the events alleged in this case. There is every reason to believe that will not change even if he is convicted, and lack of remorse is a negative at sentencing. Justice Merchan’s evaluation of Mr. Trump’s history and character may also be informed by the other judgments against him, including Justice Arthur Engoron’s ruling that Mr. Trump engaged in repeated and persistent business fraud, a jury finding that he sexually abused and defamed E. Jean Carroll and a related defamation verdict by a second jury.

Justice Merchan may also weigh the fact that Mr. Trump has been repeatedly held in contempt , warned , fined and gagged by state and federal judges. That includes for statements he made that exposed witnesses, individuals in the judicial system and their families to danger. More recently, Mr. Trump made personal attacks on Justice Merchan’s daughter, resulting in an extension of the gag order in the case. He now stands accused of violating it again by commenting on witnesses.

What this all suggests is that a term of imprisonment for Mr. Trump, while far from certain for a former president, is not off the table. If he receives a sentence of incarceration, perhaps the likeliest term is six months, although he could face up to four years, particularly if Mr. Trump chooses to testify, as he said he intends to do , and the judge believes he lied on the stand . Probation is also available, as are more flexible approaches like a sentence of spending every weekend in jail for a year.

We will probably know what the judge will do within 30 to 60 days of the end of the trial, which could run into mid-June. If there is a conviction, that would mean a late summer or early fall sentencing.

Justice Merchan would have to wrestle in the middle of an election year with the potential impact of sentencing a former president and current candidate.

If Mr. Trump is sentenced to a period of incarceration, the reaction of the American public will probably be as polarized as our divided electorate itself. Yet as some polls suggest — with the caveat that we should always be cautious of polls early in the race posing hypothetical questions — many key swing state voters said they would not vote for a felon.

If Mr. Trump is convicted and then loses the presidential election, he will probably be granted bail, pending an appeal, which will take about a year. That means if any appeals are unsuccessful, he will most likely have to serve any sentence starting sometime next year. He will be sequestered with his Secret Service protection; if it is less than a year, probably in Rikers Island. His protective detail will probably be his main company, since Mr. Trump will surely be isolated from other inmates for his safety.

If Mr. Trump wins the presidential election, he can’t pardon himself because it is a state case. He will be likely to order the Justice Department to challenge his sentence, and department opinions have concluded that a sitting president could not be imprisoned, since that would prevent the president from fulfilling the constitutional duties of the office. The courts have never had to address the question, but they could well agree with the Justice Department.

So if Mr. Trump is convicted and sentenced to a period of incarceration, its ultimate significance is probably this: When the American people go to the polls in November, they will be voting on whether Mr. Trump should be held accountable for his original election interference.

What questions do you have about Trump’s Manhattan criminal trial so far?

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Norman L. Eisen investigated the 2016 voter deception allegations as counsel for the first impeachment and trial of Donald Trump and is the author of “Trying Trump: A Guide to His First Election Interference Criminal Trial.”

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