SC21a + b The Early Atmosphere

Question 1

gases in the earths early atmosphere?

Answer 1

mainly carbon dioxide, small amounts of water vapour and other gases, little or no oxygen

Question 2

where do the earths early atmosphere gases are thought to have come from?

Answer 2

volcanoes

Question 3

evidence for no oxygen in the Earths early atmosphere?

Answer 3

~volcanoes don’t release oxygen
~iron pyrite is a compound found in very old rocks which only forms when there is no oxygen

Question 4

evidence for a large amount of carbon dioxide in the Earths early atmosphere?

Answer 4

~earth, venus and mars are planets that contain volcanoes and venus and mars have a atmosphere mainly containing CO2 thought to be from volcanoes

Question 5

how were oceans formed?

Answer 5

the earth cooled which caused the water vapour in the atmosphere cool and condense to form liquid water, oceans

Question 6

why did carbon dioxide levels decrease over millions of years?

Answer 6

carbon dioxide dissolved in the oceans reducing the amount of CO2 in the atmosphere, sea creatures used the dissolved CO2 to form shells made of calcium carbonate, CACO3, which then allowed more CO2 to dissolve

Question 7

photosynthesis equation?

Answer 7

carbon dioxide + water → glucose + oxygen

Question 8

why did oxygen levels increase?

Answer 8

some organisms use energy from the sun to make food by photosynthesis which uses carbon dioxide but releases oxygen

Question 9

earliest organism to photosynthesize?

Answer 9

cyanobacteria, live in shallow waters

Question 10

how did cyanobacteria photosynthesize?

Answer 10

~bacteria grow in huge colonies and produce a sticky mucus, which traps a layer of sand grains and other sediments.​
~the organisms need to move above the sediment layer to get sunlight.​
~over time, the sediment layers build up to form rocky shapes called stromatolites.