Chapter 10

Without the greenhouse effect, a planet's global average surface temperature would depend on only two things:

1) the planet's distance from the sun: determines the amount of energy received from sunlight. The closer a planet is to the Sun, the greater the intensity of the incoming sunlight 2) the planet's overall reflectivity, which determines the relative proportions of incoming sunlight that the planet reflects and absorbs. The higher the reflectivity, the less light absorbed and the cooler the planet.

Why don't you notice atmospheric pressure?

1) the pressure pushes in all directions, so it pushes upward and inward on you as well as downward 2) the fluids in your body push outward with an equivalent pressure, so there is not net pressure trying to compress or expand your body

atmospheric gases interact with each of these form of light in different ways:

1) x rays have enough energy to ionize almost any atom or molecule. They can therefore be absorbed by virtually all atmospheric gases. 2) Ultraviolet photons can split water (H2) molecules, and are even more likely to be absorbed by weakly bonded molecules, such as ozone (O3), which split apart in the process 4) visible light photons generally pass through atmospheric gases without being absorbed, but some are scattered so that their direction changes 4) infrared photons can be absorbed by greenhouse gases, which are molecules that easily begin rotating and vibrating

ultraviolet light and stratosphere

Above the troposphere, the air density is too low for greenhouse gases to have much effect. The primary source of heating in the stratosphere is the absorption of solar ultraviolet light by ozone. The lack of convection makes the air relatively stagnant and stratified (layered), with layers of warm air overlying cooler air. No weather and no rain: pollutants that reach including ozone destroying chemicals CFCs remain for decades.

evaporation/sublimation

After outgassing creates an atmosphere, some atmospheric gases may condense to become surface liquids or ices. If a planet warms, the rates of evaporation and sublimation will increase, adding gas to the atmosphere.

water ice on mars

Although there is no liquid water on Mars today, there is a fair amount of water ice. The fact that plenty of frozen water still remains on Mars makes it conceivable that some water is present in liquid form in underground locations where it is kept by volcanic heat.

what is an atmosphere?

An atmosphere is a layer of gas that surround a world: In most cases, it is a surprisingly thin layer. On earth, about 2/3 of the air in the atmosphere lies within 10 km of the surface. Atmospheric air is a mixture of gases that may consist either of individual atoms or of molecules. Temperatures in the terrestrial atmosphere are generally low enough for atoms to combine into molecules.

Changes in reflectivity

An increase in a planet's reflectivity means a decrease in the amount of sunlight it absorbs and vice versa. Human activity is currently altering Earth's reflectivity. Smog particles can act like volcanic dust, reflecting sunlight before it reaches the ground. Deforestation also increases reflectivity because it removes sunlight absorbing plants. On the other hand, roads and cities tend to be hotter than surrounding areas of vegetation.

Why does Earth's climate stay relatively stable?

Apparently, the strength of the greenhouse effect self-adjusts to keep the climate stable. The Co2 cycle acts as long term thermostat for earth, because it has built in form of negative feedback that returns Earth's temperature torward normal whenever it warms up or cools down. The negative feedback occurs because the overall rate at which carbon dioxide is pulled from the atmosphere is very sensitive to temperature.

where does an atmosphere end?

At some point, the density becomes so low with increased altitude that we can't really think of the gas as air anymore. On Earth, this occurs at an altitude of about 100 km; above that, the sky is black even in the daytime, much like the sky on the Moon. This altitude is often described as "the edge of space."

how the atmosphere affects planets

Atmospheres create pressure that determines whether liquid water can exist on the surface. Atmospheres absorb and scatter light. Scattering can make daytime skies bright and absorption can prevent dangerous radiation from reaching the ground. Atmosphere can create wind and weather and play a major role in long term climate change. Interactions between atmospheric gases and the solar wind can create a protective magnetosphere around planets with strong magnetic fields. Atmospheres can make planetary surfaces warmer than they would be otherwise via the greenhouse effect.

The carbon dioxide cycle

Atmospheric carbon dioxide dissolves in rainwater, creating a mild acid. The mildly acidic rainfall erodes rocks on Earth's continents and rivers carry the broken down minerals to the oceans. In the oceans, calcium from the broken down minerals combines with dissolved carbon dioxide and falls to the ocean floor, making carbonate rocks such as limestone. Over millions of years, the conveyor belt of plate tectonics carries the carbonate rocks to subduction zones, where they are carried downward. As they are pushed deeper into the mantle, some of the subducted carbonate rocks melt and release their carbon dioxide, which then outgasses back into the atmosphere through volcanoes.

x rays and the thermospheres

Because nearly all gases are good x ray absorbers, x rays from the sun are absorbed by the first gases they encounter as they enter the atmosphere. The density of gas in the exosphere is too low for it to absorb significant amounts of these x rays, so most x rays are absorbed in the thermosphere. Temperatures are quite high.

infrared light and the troposphere

Because the infrared light comes from the surface, more is absorbed closer to the ground than at higher altitudes, which is why the temperature drops with altitude in the troposphere. The troposphere is the only layer of the atmosphere with storms. The primary cause of storms is the churning of air by convection, in which warm air rises and cool air falls.

clouds

Besides being the source of precipitation, clouds can alter a planet's energy balance. Clouds reflect sunlight back to space, thereby reducing the amount of sunlight that warms a planet's surface, but they also tend to be made from greenhouse gases that contribute to planetary warming. On Earth, clouds are made from tiny droplets of liquid water or flakes of ice. Clouds are produced by condensation of water vapor. The water vapor enters the atmosphere through evaporation of surface water. Convection then carries the water vapor to high, cold regions of the troposphere, where it can condense to form clouds. Clouds can also form as winds blow over mountains. Stronger convection means more clouds and precipitation. That is why thunderstorms are common on summer afternoons, when the sunlight warmed surface drives strong convection. Equatorial regions experience high rainfall because they receive more sunlight, which causes more convection.

atmospheric pressure

Collisions of individual atoms or molecules in an atmosphere create pressure that pushes in all directions. On Earth, for example, the nitrogen and oxygen molecules in the air fly around at average speeds of about 500 meters per second. Collision create pressure that pushes in all directions, and this pressure holds up the atmosphere so that it does not collapse under its own weight. Gas in an atmosphere is held down by gravity. The atmosphere above any given altitude therefore has some weight that presses downward, tending to compress the atmosphere beneath it. At the same time, the fast moving molecules exert pressure in all directions, including upward, which tends to make the atmosphere expand. Planetary atmospheres exist in a perpetual balance between the downward weight of their gases and the upward push of their gas pressure.

water and carbon dioxide

EArth retained its outgassed water because temperatures were low enough for water vapor to condense into rain and form oceans. The oceans, in turn, explain the low level of carbon dioxide in our atmosphere. Most of the carbon dioxide outgassed by volcanism on Earth dissolved in the oceans, where chemical reactions turned it into carbonate rocks.

How is human activity changing our planet?

Earth is apparently undergoing climate change for a new reason: human activity is rapidly increasing the atmospheric concentration of carbon dioxide and other greenhouse gases. Effects of this increase in greenhouse gas concentration are already apparent: global average temperatures have risen by about .8 C in the past century.

magnetosphere

Earth's strong magnetic field creates a magnetosphere that acts like a protective bubble surrounding our planet, deflecting most solar wind particles around our planet. The magnetosphere still allows a few solar wind particles to get through, especially near the magnetic poles. Once inside the magnetosphere, these particles move along magnetic field lines, collecting in charged particle belts than encircle our planet. The high energies in these belts can be hazardous to spacecraft and astronauts passing through them.

How did Earth recover from a snowball phase?

Eventually the strengthening greenhouse effect would have warmed Earth enough to start melting the ice. In just a few centuries, Earth wold have emerged from a snow ball phase into a hothouse phase. Indeed, the end of snowball Earth episodes roughly coincides with a dramatic increase in the diversity of life on Earth. some scientists suspect that the environmental pressures cause by the snowball Earth periods may have led to a burst of evolution.

Solar wind stripping

For any world without a protective magnetosphere, particles from the solar wind can gradually strip away gas particles into space

why is the sky blue?

Gas molecules scatter blue light much more effectively than red light. The difference in scattering is so great that, for practical purposes, we can image in that only the blue light gets scattered. When the sun is overhead, the scattered blue light reaches our eyes from all directions and the sky appears blue.

snow ball earth

Geological evidence points to several particularly long and deep ice ages between about 750 and 580 million years ago. During these periods, glaciers appear to have advanced all the way to the equator. Because ice can reflect up to about 90% of the sunlgiht hitting it, this increase in global ice would have set up a positive feedback process that would have cooled Earth even further. Geologists suspect that in this way our planet may have entered the period we now call snowball earth.

thermal escape

If an atom or molecule of gas in planet's exosphere achieve escape velocity, it will fly into space. The relative important of thermal escape on any world depends on its size, distance from the sun, and asmospheric composition. In general, more thermal escape will occur if a planet is small or close to the sun.

bar

In planetary science, we measure atmospheric pressure in a unit called the bar (barometer). One bar is roughly equal to Earth's atmospheric pressure at sea level. It is also equivalent to 1.03 kilograms per square centimeter or 14.7 pounds per square inch.

the atmospheric history of venus

Its larger size allowed it to retain more interior heat, leading to greater volcanism. The associated outgassing released the vast quantities of carbon dioxide that create Venus's strong greenhouse effect.

how does the coriolis effect operate on planets?

Its strength depends on a planet's size and rotation rate: larger size and faster rotation both contribute to a stronger coriolis effect. Among the terrestrial planets, Earth is the only one with a coriolis effect strong enough to split the two large circulation cells.

past climate on mars.

Mars had wetter and warmer periods, probably with rainfall, before about 3 billion years ago. We conclude that Mars once must have had a much thicker atmosphere, with a much stronger greenhouse effect. Calculations suggest that Martian volcanoes should have outgassed enought CO2 to make the atmosphere about 400 times as dense as it is today, and enough water to fill oceans tens or even hundred of meters deep.

loss of atmospheric gas

Mars once had a denser atmosphere, but somehow have lost most of its carbon dioxide gas. This loss would have weakened the greenhouse effect until the planet essentially froze over. Some of the carbon dioxide condensed and became part of the polar caps. Some may be chemically bound into carbonate rocks. But the bulk of the gas was probably lost to space. Mars probably had a molten, convecting metals in its core. The magnetic field would have weakened as the small planet cooled and core convection ceased, leaving atmospheric gases vulnerable to being stripped into space by solar wind particles. Like carbon dioxide, some water vapor may have been stripped away by the solar wind. Because Mars lacks an ultraviolet absorbing stratosphere, atmospheric water molecules would have been easily broken apart by ultraviolet photons. This process literally rusted the Martian rocks, giving the red planet its distinctive tint.

Nitrogen, oxygen, and ozone

Nitrogen is the third most common gas released by outgassing, after water vapor and CO2. Oxgeygen is a highly reactive chemical that is easily removed from the atmosphere. the answer to the oxygen mystery is life. Plants and microorganisms release oxygen through photsynthesis. It took at least a billion years of photosynthesis before the buildup of atmospheric oxygen began. Life and oxygen also explain the presence of Earth's ultraviolet absorbing stratosphere. In the upper atmosphere, chemical reactions involving solar ultraviolet light transform some of the O2 into molecules of O3, or ozone.

losses of atmospheric gas

Planets can lose atmospheric bass in four major loss processes: condensation, chemical reactions, solar wind striping, and thermal escape. The first two of these processes simply recycle gas from the atmosphere to the planet's surface or interior, while the latter two lead to permanent loss of gas.

visible light: warming the surface and coloring the sky

Scattering sunlight has two important effects: 1)makes the daytime sky bright and prevents shadows on Earth from being pitch black 2) scattering explains why our sky is blue.

Which factors can cause long term climate change?

Scientists have identified four major factors that can lead to long term climate change on the the terrestrial worlds: solar brightening, changes in axis tilt, changes in reflectivity, changes in greenhouse gas abundance.

ionosphere

Solar X rays also ionize a small but important fraction of the thermosphere's gas. The portion of the thermosphere that contains most of the ionized gas is called the ionosphere. The ionosphere is very important to radio communication.

Chemical reactions

Some chemical reactions incorporate gas into surface metal or rock.

ice ages and other long term climate change

Such variations are possible because the CO2 cycle does not act instantly. Ice ages occur when the global average temperature drops by a few degrees. The slightly lower temperatures lead to increased snowfall, which may cover continents with ice dow to fairly low latitudes. The ice ages appear to have been strongly influenced by small changes in Earth's axis tilt and other characteristics of Earth's rotation and orbit.

do the moon and mercury have any atmosphere?

The Moon and Mercury have only extremely low-density exospheres, without any other atmospheric layers. The total amount of gas in the exopheres of the Moon and Mercury is very small. The low density of the gas means that collisions between atoms or molecules are rare. The gas particles therefore can rise as high as their speeds allow--sometimes even escaping to space. As a result, the exospheres of the Moon and Mercury extend thousands of kilometers above their surfaces.

condensation

The condensation of gases that then fall as rain, hail, or snow is essentially the reverse of the release of gas by evaporation or sublimation.

Earth's long term future climate

The continuing brightening of the Sun will eventually overheat our planet. If so, then life on Earth has already completed about 75% of its history on this planet. Earth's habitability will cease between 1 and 4 billion years from now.

how the greenhouse effect work?

The greenhouse effect works by temporarily trapping some of this infrared light, slowing its return to space. The greenhouse effect occurs only when an atmosphere contains gases that can absorb the infrared light. Gases are particularly good at absorbing infrared light are called greenhouse gases, adn they include H2O, CO2, and methane (CH4). These gases absorb infrared light effectively because their molecular structures begin rotating or vibrating when they absorb an infrared photon. A greenhouse gas molecule that absorbs an infrared photon does not retain this energy for long; instead, it quickly reemits it as another infrared photon, which may head off in any random direction. This photon can then be absorbed by another green house gas molecule, which does the same thing. The net result is that greenhouse gases tend to slow the escape of infrared radiation from the lower atmosphere, while their molecular motions heat the surrounding air. In this way, the greenhouse effect makes the surface and the lower atmosphere warmer than they would be from sunlight alone.

what is mars like today?

The low atmospheric pressure explains why liquid water is unstable and why astronauts could not survive without a pressurized spacesuit. The atmosphere is made mostly of carbon dioxide, but the total amount of gas is so small that it creates only a weak greenhouse effect. The temperature is usually well below freezing. The lack of oxgen means that Mars lacks an ozone layer, so much of the Sun's damaging ultraviolet radiation passes unhindered to the surface. Mar's more elliptical orbit puts it significantly closer to the Sun during southern hemisphere summer, giving its southern hemisphere more extreme season.

comparative structures of terrestrial atmospheres

The moon and mercury have so little gas that they essentially contain only an exosphere and have no structure to speak of. Venus, Earth, and Mars have a troposphere warmed by the greenhouse effect, and all three have a thermosphere heated by solar X rays. However, only Earth has the extra bump of a stratosphere.

how did venus get so hot?

The real question is why Venus has such a strong greenhouse effect. The simple answer is that Venus has a huge amount of carbon dioxide in the atmosphere--nearly 200,000 times as much as in Earth's atmosphere.

solar brightening

The sun has grown gradually brighter with time, increasing the amount of solar energy reaching the planets.

Changes in axis tilt.

The tilt of a planet's axis may change over long periods of time.

Surface ejection

The tiny impacts of micrometeroites, solar wind particles, and high energy solar photons can knock individual atoms or molecules from from the surface. It is not a source process for planets that already have substantial atmospheres, because the atmospheres prevent small particles and high energy solar photons from reaching the surface.

Why do atmospheric properties vary with altitude?

The way in which temperature varies with altitude determines what is often called the atmospheric structure. Earth's atmospheric structure has 4 basic layers, each which affects the planet in a distinct way: 1) troposphere 2)stratosphere 3) thermosphere 4) exosphere

mars climate and axis tilt

The weather on Mars does not change much from one year to the next. Changes in its axis tilt probably cause Mars to undergo longer term cycles of climate change. This extreme variation arises for two reasons. First, Jupiter's gravity has a greater effect on the axis of Mars than on that of Earth, because Mar's orbit is closer to Jupiter's orbit. Second, Earth's axis is stabilized by the gravity of our relatively large Moon. Mar's tiny moons are far too small to offer any stabilizing influence on its axis. Changes in axis tilt affect both the severity of the seasons and the global average temperature. The pressure therefore increases, and Mars becomes warmer as the greenhouse effect strengthens--although probably not by enough to allow liquid water to become stable at the surface.

ice in the polar crater

There cannot be liquid water on the Moon or Mercury, because the lack of significant atmospheric pressure means that water cannot remain stable in liquid form.

magnetospheres and the solar wind

There is an important type of energy coming from the Sun: the low density flow of subatomic charged particles called the solar wind.

source and loss precesses on the moon and mercury

They may once have had some gas released by volcanic outgassing, but they no longer have any volcanic activity. Some of the gas released long ago was probably lost through stripping by the solar wind. The only ongoing source of gas is he surface ejection that occurs when micrometeorites, solar wind particles, or high energy solar photons knock free surface atoms and molecules.

global average temperature

We can better appreciate the importance of the greenhouse effect by comparing each planet's average surface temperature--or global average temperature--with and without it.

the runaway greenhouse effect

To understand why Venus does not have oceans, we need to consider the role of the feedback processes--processes in which a change in one property amplifies or counteracts the behavior of the rest of the system. The runaway greenhouse effect would cause EArth to heat up until the oceans were completely evaporated and the carbonate rocks had released all their carbon dioxide back into the atmosphere. On Venus, the grater intensity of the sunlight made it just warm enough that oceans either never formed or soon evaporated, leaving Venus with a thick atmosphere full of greenhouse gases.

Where did lost water vapor and carbon dioxide go on Venus?

Venus today is incredibly dry. It is far too hot to have any liquid water or ice on its surface; it is even too hot for water to be chemically bound in surface rock, and any water deeper in its crust or mantle was probably baked out long ago. measurements also show very little water in the atmosphere. Overall, the total amount of water on Venus is about 10,000 times smaller than the total amount on EArth, a fact that explains why Venus retains so much carbon dioxide in its atmosphere: without oceans, carbon dioxide cannot dissolve or become locked away in carbonate rocks. Ultraviolet light from the Sun broke apart water molecules in Venus's atmosphere. The hydrogen atoms then escaped to sapce, ensuring that the water molecules could never re form. The oxygen from the water molecules was lost to a combination of chemical reactions with surface rocks and stripping by the solar wind. Venus's lack of a magnetic field leaves the atmosphere vulnerable to the solar wind. Venus lost a huge amoun tof hydrogen rom water molecules to space, the rare deuterium atoms would have been more likely to remain behind that the ordinary hydrogen atoms. Measurements show that this is the case. The fraction of deuterium among hydrogen atoms is a hundred times higher on Venus than on EArth, suggesting that a substantial amount of water was lost by having its molecules broken apart and its hydrogen lost to space.

How did Earth's atmosphere end up so different?

We can break this question into four separate questions: 1) Why did Earth retain most of its outgassed water--enough to form vast oceans--while Venus and Mars lost theirs? 2) Why does Earth have so little CO2 in its atmosphere compared to Venus, when Earth should have outgassed about as much of it as Venus? 3) Why is Earth's atmosphere composed primarily of nitrogen (N2) and oxygen (O2), when these gases are only trace constituent in the atmospheres of Venus and Mars? 4) Why does Earth have an ultraviolet absorbing stratosphere, while Venus and Mars do not?

size as a critical factor

We conclude that Mar's fate was shaped primarily by its relatively small size--too small to maintain the internal heat needed to keep this water and gas. As its interior cooled, its volcanoes quieted and released far less gas, while its relatively weak gravity and the loss of its magnetic field allowed existing gas to be stripped away to space. If Mars had been as large as Earth, so that it could still have outgassing and a global magnetic field, it might still have a moderate climate today. Mar's distance from the sun helped seal its fat. Mars presents us with an ominous example of how drastically things can change.

atmospheric heating and circulation cells

atmospheric heating affect global wind patterns because equatorial regions receive more heat from the Sun than polar regions. If Earth's rotation did not influence this process, the result result would be two huge circulation cells, one in each hemisphere. The circulation cells transport heat both from lower to higher altitude and from the equator to the poles.

thermosphere

begins where the temperature again starts to rise at high altitude

stratosphere

begins where the temperature stops dropping and instead begins to rise with altitude. High in the stratosphere, the temperature falls again.

aurora

charged particles trapped in the magnetosphere also create the beautiful light of the aurora. If a trapped particle gains enough energy, it can follow the magnetic field all the way down to Earth's atmosphere, where it collides with atmospheric atoms and molecules. These collisions cause the atoms and molecules to radiate and produce the moving lights of the aurora. auroras are most common near the magnetic poles and are best viewed at high latitudes.

what does a planet's reflectivity (sometimes called its albedo)

depends on its composition and color; darker colors reflect less light.

exosphere

is the uppermost region, in which the atmosphere gradually fades away into space

changes in greenhouse gas abundance

more greenhouse gases tend to make a planet warmer, and less make it cooler.

When can a planet have a stratosphere?

only if its atmosphere contains molecules that are particularly good at absorbing ultraviolet photons. Ozone (O3) plays this role on Earth, but the lack of oxygen in the atmospheres of other terrestrial worlds means that they also lack ozone. Earth is the only terrestrial world with a stratosphere, at least in our solar system.

maintaining balance

our oceans exist because Earth has a greenhouse effect that is "just right" to keep them from either freezing or boiling away, and the presence of liquid water allowed life to arise and produce oxygen. The long term existence of Earth's oceans tells us that our planet has enjoyed remarkable climate stability.

coriolis effect

planetary rotation affect global wind pattern--The Coriolis effect alters the path of air on the rotating Earth in much same way. Equatorial regions circle around Earth's rotation axis faster than polar regions. Air moving away from the equator therefore has "extra" speed that causes it to move ahead of Earth's rotation to the east, while air moving toward the equator lags behind Earth's rotation to the west. Moving air turns to the right in the northern hemisphere and to the left in the Southern Hemisphere, which explains why storms circulate in opposite directions in the two hemispheres. Uneven heated and cooling of Earth's surface creates regions of slightly higher pressure or lower pressure on average. Coriolis effect makes the inward flowing air rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The effect plays an even more important role in shaping Earth's global wind patterns: it splits each of the two huge circulation cells shown into three smaller circulation cells. In essence, the effect on a rotating planet tends to divert air moving north or south into east-west winds.

precipitation

rain, snow, and hall. Precipitation requires clouds.

climate

refers to the average of weather over many years

weather

refers to the ever varying combination of winds, clouds, temperature, and pressure that makes some days hotter or cooler, clearer or cloudier, or calmer or stormier than others

sources of atmospheric gas

terrestrial atomospheres can gain gas in three basic ways: outgassing, evaporation/sublimation, surface ejection

the exosphere

the exosphere is the extremely low density gas that forms the gradual and fuzzy boundary between the atmosphere and space. The gas density in the exosphere is so low that collisions between atoms or molecules are very rare, although the high temperature means that gas particles move quite rapidly. Light weight atoms and molecules sometimes reach escape velocity and fly off into space.

troposphere

the lowest layer, in which temperature drops with altitude (something you've probably noticed if you've ever climbed a mountain).

martian winds

the strong winds associated with the cycling of carbon dioxide gas can initiate huge dust stomrs. It can change the surface appearance over vast areas. Martian winds can also spawn dust devils, swirling winds that you may have seen over desert sands or dry dirt on Earth. Martian winds and dust storms leave Marty with perpetually dusty air, which helps explain the colors of the Martian sky.

global wind patterns

the wind direction varies with latitude: equatorial winds blow from east to west, mid-latitude winds blow from west to east, and high latitude wings blow like equatorial winds from east to west. Two factors explain this pattern: atmospheric heating and planetary rotation.

consequences of global warming

these changes will cause some regions to warm much more than the average, while other regions may actually cool. Some regions might experience more rainfall or become deserts. Polar regions will warm the most, causing ice to melt. The added effect of melting ice could increase sea level much more. Sea level could rise as much as several meters, enough to flood Florida. The most obvious way to reduce these emissions is to improve energy efficiency. Using current technology, replacing fossil fuels with alternative energy sources--such as biofuelds, solar, wind, nuclear energy--or finding ways to bury the carbon dioxide by produce of the fossil fuels that we still use.

coriolis effect on venus

venus's slow rotation means a very weak coriolis effect. As a result, Venus has little wind on its surface and never has hurricane like storms. The weak Coriolis effect also means that Venus' atmosphere has just two large circulation cells much like what Earth would have. The thick atmosphere makes the circulation so efficient at transporting heat from the equator to the poles that the surface temperature is virtually the same everywhere. Venus has no season because it has virtually no axis tilt so temperatures are the same year round. The weather is much more intersting at high altitudes.

outgassing

volcanic outgassing has been the primary source of gases for the atmospheres of Venus, Earth, and Mars. Studies of volcanic eruptions show that the most common gases released by outgassing are water, carbon dioxide, nitrogen, and sulfar bearing gases.

what creates wind and weather?

wind, rain, and other phenomena are all driven by energy in the atmosphere, which means only planets with atmospheres can have weather.

how does the greenhouse effect warm a planet?

without the greenhouse effect, Earth's surface would be too cold for liquid water to flow and for life to flourish. Let's explore how the greenhouse effect can warm planetary surfaces.