The Evolution Of The Atmosphere - Phase 1
For around 200 million years the atmosphere has been how it it now; 78% Nitrogen, 21% Oxygen and small ammounts of other gases but mainly argon (about1%) and CO2 (about 0.04%) There can also be a lot of water vapour. However it wasn't always like that...
- The surface of the earth was moltern for many millions of years and was so hot that any atmosphere just 'boiled away' into space.
- Eventually things just cooled down a bit and a very thin crust formed but volcanoes kept on errupting. These volcanoes gave out many gases like carbon dioxide, water vapor and small bits of other gases. This is how we think the oceans and atmosphere was amde.
- The theory says that the early atmosphere was mostly CO2 with practically no oxygen. Just like the atmosphere of venus & mars today.
- The oceans were made when the water vapour condensated.
The Evolution Of The Atmosphere - Phase 2 & 3
Green plants evolved and produced oxygen.
- A lot of early CO2 made, just dissolved into the oceans.
- Later on, marine organisms developed that took in some of the CO2. When they died, the organisms were buried under layers of sediment and the CO2 became 'locked up' in carbonate rocks.
- Green plants evolved over most of earth and were fine in the CO2 atmosphere.
- The plants also removed CO2 from the air and made O2 by photosynthesis. This made the oxygen level slowly rise.
Ozone layer allows evolution of complex animals.
- The build up of oxygen in the atmosphere killed off some early organisms that couldn't cope with it, but allowed other complex ones to evolve and thrive.
- The oxygen made the ozone layer (O3) that blocked harmful rays off the sun and allowed even more complex organisms to evolve, including us eventually!
- There is very, very little CO2 left now.
We know how the atmosphere has changed over the years because evidence has been found in rocks and other sources. But nobody was there millions of years ago to record changes as the happened, so all that we know about how today's atmosphere happened, are only theorys.
The atmosphere is still changing today because of...
- Human activity - burning fossil fuels (releases CO2), deforistation (contributes to increase in CO2 levels) & livestock farming (releases huge ammount of methane)
- Volcanic activity - sulphur dioxide (thrown high into the atmosphere when volcanoes errupt) & carbon dioxide (also put into the atmosphere during erruptions)
Scientists learnt alot about the past atmosphere from Antarctic ice cores. Every year a layer of ice forms and bubbles of air get trapped inside, then are burried by the next layer. The deeper the ice, the older the air. It is very dificult to be precise about how the atmosphere has changed and some of it is down to guess work.