The Earth's Atmosphere

What was the atmosphere of the earth like when it was formed 4.6 billion years ago?

Intense volcanic activity releases:

• Mainly CO₂

• Water vapour (condenses - oceans)

• Small amount of methane +ammonia

How did the atmosphere of the earth change 3 billion years ago?

Green plants & algae evolve and:

• CO₂ reduced - plants take it in and give O₂ out.

• Microorganisms that can’t tolerate O₂ are killed off.

• C from CO₂ locked in sedimentary rocks formed from shells + skeletons of marine organisms

• Other gases react with O₂ ,release N

• N produced by bacteria removing nitrates from decaying plant material

How has the atmosphere of the earth changed now?

• 20% oxygen and 80% nitrogen

• Carbon dioxide decreased alot.

Why have the levels of oxygen increased over time?

• Algae and plants started to photosynthesise 2.7 billion years ago

• Plants evolved ,O₂ levels increased.

• Eventually O₂ levels increased enough to allow animals to evolve.

How have plants and algae caused the levels of carbon dioxide to decrease over time?

Plants and algae evolved, using more carbon dioxide during photosynthesis.

How has carbon caused the levels of carbon dioxide to decrease over time?

Carbon becomes locked up in sedimentary (limestone) rocks and fossil fuels. (coal, crude oil, natural gas)

What is limestone?

Contains calcium carbonate, formed from shells and skeleton of sea creatures.

What is coal?

Sedimentary rock formed from plant deposits that were buried + compressed over million of years.

How has sea water caused the levels of carbon dioxide to decrease over time?

Carbon dioxide and sea water react to produce:

• Insoluble carbonates that are deposited as sediment

• Soluble hydrogen carbonates

Why is carbon dioxide a risk for marine life?

Too much carbon dioxide dissolving in oceans can harm sea life, such as coral reefs.