Origin of Earth’s Atmosphere Early Earth was HOT!

Why? Accretion; Radioactive decay of elements

Consequences - Constant volcanism, surface temperature too high for liquid water or life as we know it, molten surface or thin, unstable basaltic crust.

Cooling led to: Condensation & accumulation of surface water

Changing atmosphere due to volcanic out-gassing

The right conditions for the evolution of life

Source: http://www.ux1.eiu.edu/~cfjps/1400/atmos_origin.html

1st Atmosphere

Composition - H2, He

Lost to space early in Earth's history because: Earth's gravity is not strong enough to hold lighter

gases

Earth still did not have a differentiated core (solid inner/liquid outer core) which creates Earth's magnetic field (magnetosphere = Van Allen Belt) which deflects solar winds.

Once the core differentiated the heavier gases could be retained

2nd AtmosphereProduced by volcanic out-gassing.H2O, CO2, SO2, CO, S2, Cl2, N2, H2 and

NH3 (ammonia) and CH4 (methane)

No free O2 at this time

Ocean Formation - As the Earth cooled, H2O produced by out-gassing could exist as liquid in the early Archean, allowing oceans to form.

The Earth in its earliest years was a horribly hot and violent place. Asteroids, comets, and other chunks of space debris left over from the solar system's formation continually bombarded the young planet, releasing huge amounts of heat, and bringing water in the form of ice to Earth.

Addition of O2Photochemical dissociation - breakup of

water molecules by UV radiation Produced O2 levels approx. 1-2% current levels

At these levels O3 (Ozone) can form to shield Earth surface from UV

Photosynthesis – CO2 + H2O + sunlight glucose + O2

O2 produced by cyanobacteria, and eventually higher plants, such as stromatolites

This process produced most of Earth’s oxygen.

Present Composition78% Nitrogen

21% Oxygen

1% Other trace gases

Layers of the Atmosphere

Caused by temp. differences

These differences result from how solar energy is absorbed as it moves through the atmosphere

http://www.aerospaceweb.org/question/atmosphere/atmosphere/layers.gif

4 Main Layers of the Atmosphere

http://www.epa.gov/apti/course422/images/fig-1.gif

http://www.greenfacts.org/images/glossary/stratosphere-troposphere.jpg

TroposphereClosest to EarthNearly all weather occurs hereAlmost all H2O vapor and CO2

Temp. decreases with altitude because air in this layer is heated from below by thermal energy that is re-radiated from Earth’s surface

Tropopause

Upper boundary of the troposphere

Jet stream

-Varies with latitude & seasons

-250 mph

-East wind

Stratosphere16 – 50 kmOzone layer is hereTemp. increases because air is heated from above by absorption of solar radiation by ozone

Jets fly here to avoid turbulenceStratopause - upper boundary

Ozone LayerOzone is made of 3 atoms of oxygen (O3)

≈ 2-3 mm thick if it were at sea level

Purpose - absorbs harmful UV radiation from the Sun

Mesosphere50 – 85 kmTemp. decreases as altitude increases

Mesopause - Upper boundaryAvg Temp. = - 90oCCOLDEST layer in the atmosphereMeteors begin to disintegrate here

Thermosphere

90 km ~ 1000 kmSpace begins here (~100 km)Temp. increases as altitude increasesCan’t read temp. with a thermometer because air particles are too far apart

Space Shuttle & ISS orbit hereIonosphere is the lower regionAurora occur here

ExosphereEnd of the atmosphere

Almost a vacuum

Where light elements escape Earth’s gravity

http://curriculum.calstatela.edu/courses/builders/lessons/less/les3/les3gifs/layers.gif