The Earth’s Atmosphere The Earth’s Atmosphere

Michael BeattieMichael Beattie

OverviewOverview

• The Earth is surrounded by a blanket of air, which we The Earth is surrounded by a blanket of air, which we call the atmosphere.call the atmosphere.

• It reaches over 640 km from the surface of the Earth.It reaches over 640 km from the surface of the Earth.• Almost 99% of the atmosphere lies within 64-80 km Almost 99% of the atmosphere lies within 64-80 km

of the earth’s surface.of the earth’s surface.• This thin blanket of air shields the surface and its This thin blanket of air shields the surface and its

inhabitants from the sun’s UV radiant energy, as well inhabitants from the sun’s UV radiant energy, as well as from material from interplanetary space.as from material from interplanetary space.

• There is no definite upper limit to the atmosphere; There is no definite upper limit to the atmosphere; rather, it becomes thinner and thinner, eventually rather, it becomes thinner and thinner, eventually merging with the empty space that surrounds all the merging with the empty space that surrounds all the planets.planets.

Composition of the Composition of the AtmosphereAtmosphere• The atmosphere is composed of 78% nitrogen, 21% The atmosphere is composed of 78% nitrogen, 21%

oxygen, 0.9% argon, 0.03% carbon dioxide, and trace oxygen, 0.9% argon, 0.03% carbon dioxide, and trace amounts of other gases. amounts of other gases.

• At the surface there is a balance between usage and At the surface there is a balance between usage and production of these gases.production of these gases.

• Nitrogen is removed from the atmosphere primarily by Nitrogen is removed from the atmosphere primarily by biological processes that involve soil bacteria.biological processes that involve soil bacteria.

• It is returned mainly through the decaying of plant and It is returned mainly through the decaying of plant and animal matter.animal matter.

• Oxygen is removed from the atmosphere during breathing, Oxygen is removed from the atmosphere during breathing, as the lungs take in oxygen and release carbon dioxide.as the lungs take in oxygen and release carbon dioxide.

• It is returned during photosynthesis, as plants, in the It is returned during photosynthesis, as plants, in the presence of sunlight, combine carbon dioxide and water to presence of sunlight, combine carbon dioxide and water to produce sugar and oxygen. produce sugar and oxygen.

Composition of the Composition of the AtmosphereAtmosphere• Water vapor is an extremely important gas in our Water vapor is an extremely important gas in our

atmosphere.atmosphere.• Its concentration in the atmosphere varies greatly from Its concentration in the atmosphere varies greatly from

place to place, and from time to time.place to place, and from time to time.• Close to the surface in warm, tropical locations, water vapor Close to the surface in warm, tropical locations, water vapor

may account for up to 4% of atmospheric gases, whereas in may account for up to 4% of atmospheric gases, whereas in colder arctic areas, its concentration may dwindle to a mere colder arctic areas, its concentration may dwindle to a mere fraction of a percent.fraction of a percent.

• It forms into cloud particles that grow in size and fall to the It forms into cloud particles that grow in size and fall to the earth as precipitation.earth as precipitation.

• It is also provides an important source of atmospheric It is also provides an important source of atmospheric energy in latent heat when it changes from vapor into liquid energy in latent heat when it changes from vapor into liquid water or ice. water or ice.

• Latent heat is an important source of energy for storms, Latent heat is an important source of energy for storms, such as thunderstorms and hurricanes.such as thunderstorms and hurricanes.

Composition of the Composition of the AtmosphereAtmosphere• Carbon dioxide is present as a small but important Carbon dioxide is present as a small but important

percentage of air (about 0.037%).percentage of air (about 0.037%).• It enters the atmosphere mainly from the decay of It enters the atmosphere mainly from the decay of

vegetation, but it also comes from volcanic eruptions, vegetation, but it also comes from volcanic eruptions, from the burning of fossil fuels, and from from the burning of fossil fuels, and from deforestation.deforestation.

• The removal of carbon dioxide from the atmosphere The removal of carbon dioxide from the atmosphere takes place during photosynthesis.takes place during photosynthesis.

• Recent measurements of carbon dioxide show a 15% Recent measurements of carbon dioxide show a 15% increase in the atmospheric concentration since 1958.increase in the atmospheric concentration since 1958.

• This increase means carbon dioxide is entering the This increase means carbon dioxide is entering the atmosphere at a greater rate than it is being removed.atmosphere at a greater rate than it is being removed.

• The increase appears to be due mainly to the burning The increase appears to be due mainly to the burning of fossil fuels; however, deforestation also plays a role. of fossil fuels; however, deforestation also plays a role.

Composition of the Composition of the AtmosphereAtmosphere• Carbon dioxide like water vapor is a Carbon dioxide like water vapor is a

greenhouse gas, meaning it traps a portion of greenhouse gas, meaning it traps a portion of the earth’s outgoing energy.the earth’s outgoing energy.

• As the atmospheric concentration of carbon As the atmospheric concentration of carbon dioxide increases, so should the average dioxide increases, so should the average global surface air temperature.global surface air temperature.

• Most mathematical model experiments that Most mathematical model experiments that predict future atmospheric conditions estimate predict future atmospheric conditions estimate that increasing carbon dioxide levels, along that increasing carbon dioxide levels, along with other greenhouse gases, will result in a with other greenhouse gases, will result in a global warming of surface air between 1 and global warming of surface air between 1 and 3.5 degrees Celsius by the year 2100.3.5 degrees Celsius by the year 2100.

The Early AtmosphereThe Early Atmosphere

• The atmosphere that originally surrounded the earth was The atmosphere that originally surrounded the earth was probably much different from the air we breathe today.probably much different from the air we breathe today.

• The earth’s first atmosphere, about 4.6 billion years ago, The earth’s first atmosphere, about 4.6 billion years ago, most likely consisted of hydrogen and helium, the two most likely consisted of hydrogen and helium, the two most abundant gases found in the universe.most abundant gases found in the universe.

• Most scientists feel that this early atmosphere escaped Most scientists feel that this early atmosphere escaped into space from the earth’s hot surface.into space from the earth’s hot surface.

• A second, more dense atmosphere gradually developed as A second, more dense atmosphere gradually developed as gases from molten rock within the earth’s hot interior gases from molten rock within the earth’s hot interior escaped through volcanoes and steam vents.escaped through volcanoes and steam vents.

• The gases were mostly water vapor (about 80%), carbon The gases were mostly water vapor (about 80%), carbon dioxide (about 10%) and up to a few percent nitrogen.dioxide (about 10%) and up to a few percent nitrogen.

The Early AtmosphereThe Early Atmosphere

• Oxygen began an extremely slow increase in Oxygen began an extremely slow increase in concentration as rays from the sun split water concentration as rays from the sun split water vapor into hydrogen and oxygen.vapor into hydrogen and oxygen.

• The hydrogen, being lighter, probably rose The hydrogen, being lighter, probably rose and escaped into space, while the oxygen and escaped into space, while the oxygen remained in the atmosphere.remained in the atmosphere.

• This slow increase in oxygen may have This slow increase in oxygen may have provided enough of this gas for primitive provided enough of this gas for primitive plants to evolve, and as plant growth plants to evolve, and as plant growth increased our atmosphere was greatly increased our atmosphere was greatly enriched with oxygen. enriched with oxygen.

Air Density and PressureAir Density and Pressure

• Air density is greatest at the surface and Air density is greatest at the surface and decreases as we move up into the decreases as we move up into the atmosphere; rapidly at first, then more atmosphere; rapidly at first, then more slowly as we move farther from the surface.slowly as we move farther from the surface.

• The weight of all the air around the earth is The weight of all the air around the earth is 5600 trillion tons.5600 trillion tons.

• Atmospheric pressure always decreases Atmospheric pressure always decreases with increasing height.with increasing height.

• Normal atmospheric pressure near sea Normal atmospheric pressure near sea level is 1013.25 mb or 14.7 pounds per level is 1013.25 mb or 14.7 pounds per square inch.square inch.

Layers of the AtmosphereLayers of the Atmosphere

• TroposphereTroposphere: The troposphere is the lowest region in the : The troposphere is the lowest region in the earth's atmosphere. On the earth, it goes from ground level earth's atmosphere. On the earth, it goes from ground level up to about 17 kilometers high. The weather and clouds up to about 17 kilometers high. The weather and clouds occur in the troposphere. In the troposphere, the occur in the troposphere. In the troposphere, the temperature generally decreases as altitude increases. temperature generally decreases as altitude increases.

• TropopauseTropopause: The tropopause is the boundary zone (or : The tropopause is the boundary zone (or transition layer) between the troposphere and the transition layer) between the troposphere and the stratosphere. The tropopause is characterized by little or no stratosphere. The tropopause is characterized by little or no change in temperature as altitude increases. change in temperature as altitude increases.

• StratosphereStratosphere: The stratosphere is characterized by a : The stratosphere is characterized by a slight temperature increase with altitude and the absence slight temperature increase with altitude and the absence of clouds. The stratosphere extends between 17 to 50 of clouds. The stratosphere extends between 17 to 50 kilometers above the earth's surface. The earth's ozone kilometers above the earth's surface. The earth's ozone layer is located in the stratosphere. Ozone, a form of layer is located in the stratosphere. Ozone, a form of oxygen, is crucial to our survival; this layer absorbs a lot of oxygen, is crucial to our survival; this layer absorbs a lot of ultraviolet solar energy. ultraviolet solar energy.

Layers of the AtmosphereLayers of the Atmosphere

• MesosphereMesosphere: The mesosphere is characterized by temperatures : The mesosphere is characterized by temperatures that quickly decrease as height increases. The mesosphere extends that quickly decrease as height increases. The mesosphere extends from between 50 and 80 kilometers above the earth's surface. from between 50 and 80 kilometers above the earth's surface.

• IonosphereIonosphere: The ionosphere starts at about 70-80 km high and : The ionosphere starts at about 70-80 km high and continues for hundreds of kilometers (about 640 km). It contains continues for hundreds of kilometers (about 640 km). It contains many ions and free electrons (plasma). The ions are created when many ions and free electrons (plasma). The ions are created when sunlight hits atoms and tears off some electrons. Auroras occur in sunlight hits atoms and tears off some electrons. Auroras occur in the ionosphere. the ionosphere.

• ThermosphereThermosphere: The hot layer above the mesosphere. In the : The hot layer above the mesosphere. In the thermosphere there are relatively few atoms and molecules. thermosphere there are relatively few atoms and molecules. Consequently, the absorption of a small amount of solar energy can Consequently, the absorption of a small amount of solar energy can cause a large increase in air temperature that my exceed 500 cause a large increase in air temperature that my exceed 500 degrees Celsius.degrees Celsius.

• Exosphere: Exosphere: The exosphere is the outermost layer of the Earth's The exosphere is the outermost layer of the Earth's atmosphere. The exosphere goes from about 640 km high to about atmosphere. The exosphere goes from about 640 km high to about 1,280 km. The lower boundary of the exosphere is called the critical 1,280 km. The lower boundary of the exosphere is called the critical level of escape, where atmospheric pressure is very low (the gas level of escape, where atmospheric pressure is very low (the gas atoms are very widely spaced) and the temperature is very low. atoms are very widely spaced) and the temperature is very low.