1. Past and Present of the Earth’s Atmosphere

2. Important gases in the Atmosphere:
Allows photosynthesis, important greenhouse gas
Allows respiration, forms ozone
Blocks harmful solar radiation
Greenhouse gas
Carbon dioxide
Oxygen
Ozone
Methane
Add Nitrogen??? Also important to life, not as a gas but it has to be ‘fixed’ to be useable by most organisms

3. Past and Present Composition
The composition of the Earth’s atmosphere has changed since the formation of the Earth. The Earth’s first atmosphere was mainly helium and hydrogen. Volcanic emissions later added carbon dioxide, nitrogen, water, sulfur dioxide and other elements.

4. hydrogen and helium only
4.5 billion years ago
hydrogen and helium only
Intense solar radiation
No life or oceans.
4.0 billion years ago
carbon dioxide, nitrogen present in atmosphere
produced by volcanic emission of gases.
Intense solar radiation
Oceans form

5. Large amounts of carbon dioxide from volcanoes caused the Earth’s past climate to be warmer than today’s (~200 F or more?)
Without carbon dioxide no life could be present on earth. Primitive bacteria and algae in oceans could now do photosynthesis.

6. Oceans form!! Water on the earth vaporized first
Then condensed in the atmosphere
Then it rained for millions of years!!
Oceans were green and full of iron (Fe)

7. But no life on land due to solar radiation from the sun.
But life in oceans is protected from radiation and can develop due to presence of carbon-dioxide

8. 4 billion years ago
Radiation can’t penetrate the ocean water.
Carbon dioxide allows photosynthesis to take place.
First life appears in oceans as primate anaerobic bacteria which don’t produce oxygen!
3.5 billion years ago Cyanobacteria appear (blue-green algae) which produce oxygen which kills off other bacteria
The O2 produced is used up in chemical reactions and does not build up as free oxygen in atmosphere. The oxygen reacted with dissolved iron in sea water to form iron oxide compounds on the ocean floor.

10. Stromatolite reefs contain a mixture of anaerobic and aerobic bacteria
Stromatolite reefs contain a mixture of anaerobic and aerobic bacteria. These are the descendants of the first oxygen makers
Cyanobacterium

11. Sunlight + CO2 + H2O  O2 (g) + C6H12O6
Free oxygen gas was absent in the earth’s early atmosphere.
Any oxygen produced by photosynthesis reacted with other chemicals and was trapped in the form of oxide compounds in rock, Fe2O3 .
It took millions of years before oxygen was present as a gas in the atmosphere
Nearly all the molecular oxygen in the atmosphere today was produced by photosynthesis.
Sunlight + CO2 + H2O  O2 (g) + C6H12O6
Living organisms are responsible for the evolution of our atmosphere. Free oxygen made it possible for life to evolve on land.
Before large amounts of free oxygen were present in the atmosphere, lethal intensities of solar radiation flooded the Earth’s surface.
Free oxygen reacts in the stratosphere to form ozone (O3). This ozone layer shields the Earth’s Surface from lethal radiation.

12. Banded Iron deposits are now one of the main sources of iron ore.
They formed when cyanobacteria produced oxygen which reacted with dissolved iron to form rust. This precipitated onto the ocean floor.
Our cars and bridges are made of materials created by bacteria!

13. 2 Billion years ago:
Iron in oceans is oxidized > Oceans from green to blue
O2 produced by photosynthesis can now build up in atmosphere as free O2 (g)
This oxygen is hit by solar radiation and forms ozone. The Ozone layer forms blocks most harmful radiation.
1.5 Billion years ago:
Ozone layer thick enough to block enough DNA-inactivating radiation to allow life on land to evolve

14. Earth’s 3rd atmosphere forms (today’s)
Earth’s 3rd atmosphere forms (today’s). Rich in nitrogen, oxygen, argon, carbon dioxide.
Most harmful radiation is blocked by ozone layer.
Greenhouse gases like water, carbon dioxide and methane trap long-wave length energy emitted from surface of Earth and keep Earth warmer than it should be.
Average surface temperature is 15C rather than the -6C it would be without greenhouse gases.

15. Just the right amount of ozone is a good thing!
Ultra-violet light in the range of angstroms will break down DNA.
Ozone blocks this short-wave length light from hitting the surface of the Earth.
This is why we banned CFCs that destroy the earth’s ozone layer!

16. In the time of dinosaurs…
The earth was warm, swampy
There was a lot of volcanic activity!!
Oxygen levels were higher
CO2 levels were up to 5 times higher than today
As a result huge tropical swampland covered much of the earth
All this food allowed the dinosaurs to get HUGE!

17. What if our atmosphere was different?
Our carbon dioxide and oxygen levels are lower than in the past
Different plants and animals grow today
A bit more oxygen would allow insects to get big again
INTERESTING THOUGHTS!!!

18. Present composition of the lower Atmosphere
Water vapor varies depending on the location. From 0.01% to 5%

21. Doesn’t make sense, I thought we have less oxygen now, slide shows more oxygen now than in past?

22. Oxygen produced by photosynthesis builds up in the atmosphere
Oxygen produced by photosynthesis builds up in the atmosphere. This turns into ozone due to solar radiation.