9.1 The composition & evolution of the Earth's atmosphere
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Describe the proportions of gases in the modern atmosphere
● 78% nitrogen ● 21% oxygen ● 1% carbon dioxide & noble gases
Describe the Earth’s early atmosphere and how it was formed
● The Earth was hot when it was formed ● There was significant volcanic activity ● Gases have been released from these volcanoes ● These gases included: CO2, N2, CH4, NH3, H2O
How did the amount of oxygen in the atmosphere increase?
Algae and plants produced the atmospheric O2 by photosynthesis, which can be represented by the equation: 6CO2+ 6H2O → C6H12O6 + 6O2 As the amount of gradually O2 increased, there were more plants that produced more oxygen.
How did the amount of carbon dioxide in the atmosphere decrease?
● Some CO2 was dissolved in the oceans, where it reacted with metal ions to form insoluble carbonates, such as CaCO3, or was taken in by animals to become a part of skeleton. When an animal dies, this becomes a sedimentary rock. ● Some CO2 was used in photosynthesis to make oxygen.