Past and Present of the Earth’s Atmosphere

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

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.

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

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.

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)

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

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.

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

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.

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!

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

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.

Just the right amount of ozone is a good thing! Ultra-violet light in the range of 2000 - 2900 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!

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!

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!!!

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

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

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.