Understanding Our Atmosphere

SOL ES 12: Understanding the origin and evolution of the

atmosphere and the interrelationship of geologic,

biologic and human activities on its composition and dynamics

Origin of the atmosphere

• The original atmosphere–Probably made up of hydrogen and helium.

–These are fairly common in the universe.

• Original atmosphere stripped away by the solar wind –H and He are very light

• Hydrogen and helium have the smallest atoms by mass.

–The early earth was not protected by a magnetic field.

–Thus the current atmosphere is secondary

The secondary atmosphere• Formed from degassing of

volcanoes• Also comets which are made of

rock and ice.

• Gasses emitted probably similar to the gasses emitted by volcanoes today.– H2O (water), 50-60%– CO2 (carbon dioxide), 24%– SO2 (sulfur dioxide), 13%

Modern atmosphere• Nitrogen (N2)- • 78%, • Oxygen (O2)- • 21%,• Carbon Dioxide

(CO2) 0.03 %,

• Where did all the oxygen come from? 78%

21%

Life changes the atmosphere• Oxygen came from Cyanobacteria (blue-

green algae) that used photosynthesis. This is what plants use to take carbon dioxide out of the atmosphere and release oxygen.

Over time, more Photosynthetic organisms evolve.

These organisms (such as stromatolites) use CO2 and produce oxygen (O2) as a waste product.

Carbon Cycle in our Atmosphere

• Where did the O2 come from?

–Produced by photosynthetic life.

• Where did the CO2 go?

– Dissolves in water in the oceans (Carbon Sink)

– Used by life through photosynthesis and buried when plants and micro-organisms die.

• The source of coal and oil

Layers of the Atmosphere

Summary of Layers

• Troposphere: Layer where all life is and where all weather happens. It’s where we live.– Gets colder as you go up.

• Stratosphere: Layer above the troposphere. Includes the OZONE LAYER, that traps heat.– Stratosphere is very hot as you

move upward!

• Mesosphere: Middle layer. Above the stratosphere. Gets colder as you go up because it lacks Ozone.

• Thermosphere: Means heated layer. Gets hotter upward because it’s close to the sun.

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Changes in the Atmosphere with Altitude

• Air Pressure decreases as you go up. Happens for 2 reasons.

1.) There are fewer molecules of air as you go up.

2.) These air molecules are farther apart.

• There is also less Oxygen as you go upward. – This is why you can get altitude

sickness if you climb a tall mountain.

– Why football teams go to Denver early to practice.

– Why an airplane is pressurized and has oxygen masks.

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The other planets• Venus

–Closer to the sun

–Very hot at the surface so water vapor in the atmosphere does not condense.• Runaway greenhouse effect

(482oC, 900oF).

–No oceans or rainfall so CO2 does not dissolve.

–Has a very dense atmosphere.

The other planets• Mars

–Further from the sun

–Smaller than Earth

–Most of the atmosphere escaped into space.

–No oceans (at least now)

–98% of atmosphere is CO2.

• Jupiter – Huge (318x earth’s mass)

– Kept all its original atmosphere

– 80% Hydrogen– 20% Helium

Summary1st atmosphere

H and He from solar nebula

Lost to solar wind

2nd atmosphere

H20, CO2 and SO2 from volcanic degassing

Transformed by photosynthesis

Current atmosphere

N2, O2, from photosynthesis and constant N2 production

78% Nitrogen21% Oxygen1% Trace gasses