Atmospheric changes

Atmosphere

A thin layer of gases surrounding Earth

Percentage of oxygen in modern atmosphere

20%

Percentage of nitrogen in modern atmosphere

80%

Other gases in the modern atmosphere

CO2, H2O, Noble gases

Age of the earth

4.6 billion years

Age of the modern atmosphere

~20 million years

Composition of the early atmosphere

CO2, H2O, Nitrogen

Water vapour decreased

Because water condensed as the earth cooled, forming oceans

Carbon dioxide decreased

dissolving in the oceans, forming sedimentary rocks, photosynthesis

The early atmosphere was formed by

Volcanoes

Photosynthesis

Carbon dioxide + water = glucose + oxygen

Oxygen increased

by photosynthesis of algae and bacteria

Sedimentary rocks

Rock that forms when sediments such as carbonates and dead organisms are squashed together over time