11.2 our evolving atmosphere
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what happens after carbon dioxide is taken in by plants and converted into glucose and oxygen during photosynthesis
• carbon in glucose can then end up in new plant material • when animals eat the plants, some of this carbon can be transferred to animal tissues
where can the carbon from plants be transferred to in animals
skeletons and shells
what happens over millions of ears as skeletons and shells build up at the bottom of oceans
• they become covered with layer upon layer of fine sediment • eventually the deposits form sedentary carbonate rocks such as limestone (contains calcium carbonate)
how are fossil fuels, coal, crude oil and natural gas formed
some of the remains of living things were crushed by large-scale movements of the earth and heated within the earth’s crust over very long periods of time
what is coal classified as
a sedimentary rock
how is coal formed
• thick deposits of plant material such as ancient trees and ferns • when the plants died in swamps they were buried in the absence of oxygen and compressed over millions of years
how is crude oil and gas formed
• from the remains of plankton deposited in muds on the seabed • remains covered by sediments that became layers of rock when compressed over millions of years • crude oil and natural gas formed is found trapped beneath these layers of rock
what is another way in which carbon dioxide was removed from the early atmosphere
• by dissolving in water of the oceans • reacted with metal oxides to form insoluble carbonate compounds • these fell to the seabed as sediment and helped to form more carbonate rocks
why has the level of co2 not changed much over the past 200 million years
due to the natural cycle of carbon in which carbon moved between the oceans, rocks and the atmosphere
what gases do volcanoes emit
• nitrogen (n2) • methane (CH4) • ammonia gases (NH3)
how does methane react with oxygen formed by evolving algae and plants?
CH4 + 2O2 –> CO2 + 2H2O
how does ammonia react with oxygen formed by evolving algae and plants
4NH3 + 3O2 –> 2N2 + 6H2O
what happened when ammonia and methane reacted with oxygen
• removed the methane and ammonia from the atmosphere • levels of nitrogen in the atmosphere could build up because nitrogen is an unreactive gas
when did the proportions of gases in the Earth’s atmosphere stabilise (they are the same today)
200 million years ago
what is the percentage of gases in the atmosphere
• Nitrogen: 79% • Oxygen: 21% • Argon: 0.9% • Carbon dioxide: 0.04%