Earth’s Early Atmosphere

First Atmosphere

• Probably H2 or He– Rare on our planet, lost to space because:• Gravity not strong enough to hold lighter gases• No magnetosphere (Van Allen belt) to deflect solar

winds

• Once we had a differentiated core, the heavier gases could be retained.

Side note: Some of those solar particles hit our upper atmosphere

Developing Atmosphere• Produced by volcanoes• Probably H2O, CO2, SO2, CO, S2,

Cl2, N2, H2, NH3, and CH4

• As Earth cooled...

Here comes the Oxygen!

• Produced in two ways:– Photochemical dissociation

• Sun breaks up water with UV rays• 1-2% of Oxygen made this way• Now Ozone (O3) can form! (we’ll get to this in a second)

– Photosynthesis• CO2 + H2O + sun organic compounds + OXYGEN produced by

cyanobacteria and higher plants

• Evidence of this is shown in the rock history. There is less and less Oxygen in rocks as you go back in time.

What is Ozone?

• Diatomic Oxygen is TWO atoms of oxygen bonded together to form oxygen gas.

• Ozone is THREE oxygenatoms bonded together.

What does Ozone Do?

• It absorbs most of the harmful UV rays that enter out atmosphere.

• Up high in the atmosphere, it is beneficial.• At ground level, it is a pollutant and is harmful

to our health.• Ever smell that metallic tang near electrical

motors?

So, now that we have some Oxygen…. Where does this Ozone come from?

First, we have to look at how our atmosphere is structured…..

The ozone layer is found in the Stratosphere

Formation of Ozone by UV rays

The Truth

• Science is still not decided on the Ozone layer being destroyed by CFCs

• The Montreal Treat (to ban CFCs) was decided on without concrete data… only theories.

• Much of the studies and data used to “prove” the ozone depletion are faulty or politically driven.

• A 10% decrease in ozone would be the equivalent of moving 60 miles closer to the equator.– Moving from New York to Florida raises your UV exposure

by 200%.

What you need to know for the Test

• The hole in the ozone layer threatens life because of raised UV penetration.

• It is caused by CFCs, Chlorofluorocarbons.• We must use less CFCs in aerosols, refrigerants

(AC liquids), use less foam insulation with CFCs, no halon fire extinguishers, or cleaners with CFCs.

• One Chlorine or bromine atom can destroy 100,000 ozone molecules during its life.