Topic 1 - The Earth's Sea and Atmosphere

Question 1

Describe phase 1 of the earths atmosphere

Answer 1

• the earths surface was originally molten, it was so hot that any atmosphere just boiled away into space
• eventually it cooled and a thin crust formed but volcanoes kept erupting
• the volcanoes have out lots of gas including carbon dioxide and water vapour which is thought to be how the oceans and atmosphere were formed
• according to this theory the early atmosphere was mostly co2 (similar to Mars and Venus today)
• the oceans formed when the water vapour condensed

Question 2

Describe phase 2 of the earths atmosphere

Answer 2

• lots of the co2 dissolved into the oceans
• marine organisms developed which took in some of this co2. When they died they were buried under layers of sediment and the co2 became ‘locked up’ in carbonate rocks
• green plants evolved over most of the earth
• green plants also removed co2 from the air and produced oxygen (photosynthesis) which cause the oxygen level to gradually increase

Question 3

Describe phase 3 of the earths atmosphere

Answer 3

• the build up of oxygen killed off some early organisms that couldn’t tolerate it but allowed more complex organisms to evolve
• the oxygen created the ozone layer which blocked harmful rays from the sun and enabled more complex organisms to evolve
• there is very little co2 left now

Question 4

Why is today’s atmosphere still changing ?

Answer 4

Human activity - burning fossil fuels, deforestation,overstock farming
Volcanic activity - sulfur dioxide reacts with sunlight, water, oxygen and dist to form volcanic smog. Carbon dioxide is also released

Question 5

How do we know about the evolution of the atmosphere ?

Answer 5

Each year a layer of ice forms in the Antarctic and bubbles of air get trapped inside it. The deeper the ice the older the air. By examine different bubbles you can see how the air has changed. Nobody was actually there at the time since it’s difficult to be precise.