C9 The Evolution of the Atmosphere (page 157)

Question 1

Regarding evolution, what do Phase 1 mean?

Volcanoes gave out gasses? Explain

Answer 1

1) The first billion years of Earths history were pretty explosive - the surface was covered in volcanoes that erupted and released lots of gasses. We think this was how the early atmosphere was formed.

2) The early atmosphere was probably mostly carbon dioxide, with virtually no oxygen. This is quite like the atmospheres of Mars and Venus today.

3) Volcanic activity also released Nitrogen, which built up in the atmosphere over time, as well as water vapour and small amounts of methane and ammonia.

Question 2

Regarding evolution, what do Phase 2 mean?

Oceans, Algae and Green plants absorbed Carbon Dioxide?

Answer 2

1) When the water vapour in the atmosphere condensed, it formed the oceans.

2) Lots of carbon dioxide was removed from the early atmosphere as it dissolved in the oceans. This dissolved carbon dioxide then went through a series of reactions to form carbonate precipitates that formed sediments on the seabed.

3) Green plants and algae evolved and absorbed some of the carbon dioxide so that they could carry out photosynthesis. Later, marine animals evolved. Their shells and skeletons contained corbonates from the oceans.

4) Some of the carbon these organisms took in from the atmosphere and oceans became locked up in rocks and fossil fuels after the organisms died.

When plants, plankton and marine animals die, they fall to the seabed and get buried by layers of sediment. Over millions of years, they become compressed and form sedimentary rocks, oil and gas - trapping the carbon within them and helping to keep carbon dioxide levels in the atmosphere reduced.

Things like coal, crude oil and natural gas that are made by this process are called ‘fossil fuels’.

Question 3

Crude oil and natural gas are formed from what deposits?

Answer 3

plankton. These fossil fuels form reserviors under the seabed when they get trapped in rocks.

Question 4

Coal is a sedimentary rock made from what?

Answer 4

thick plant deposits.

Question 5

Limestone is also a sedimentary rock. Its mostly made of what?

Answer 5

calcium carbonate deposits from the shells and skeletons of marine organisms.

Question 6

Regarding evolution, what do Phase 3 mean regarding

Green plants and Algae produced Oxygen? Explain

Answer 6

1) As well as absorbing the carbon dioxide in the atmosphere, green plants and algae produced oxygen by photosynthesis - this is when plants use light to convert carbon dioxide and water into sugars:

Carbon dioxide + Water &raquo_space;» glucose + oxygen
light
6CO2 + 6H2O &raquo_space;» C6H12O6 + 6O2

2) Algae evolved first - about 2.7 billion years ago. Then over the next billion years or so, green plants also evolved.

3) As oxygen levels built up in the atmosphere over time, more complex life (like animals) could evolve.

4) Eventually, about 200 million years ago, the atmosphere reached a composition similar to what it is today:

approximately 80% nitrogen, 20% oxygen and small amounts of other gasses (each only makes up less than 1% of the atmosphere), mainly carbon dioxide, noble gasses and water vapour.

Question 7

Describe how sedimentary rocks are formed? (2 marks)

Answer 7

Sedimentary rocks are formed when organic matter such as plant deposits or the shells and skeletons dead of marine animals fall to the seabed (1 mark)

These become buried and compressed by sediments over millions of years forming rocks (1 mark)

Question 8

We’ve learnt about the atmosphere from Antarctic ice cores.

Each year a layer of ice forms with bubbles of air trapped in it, what can this tell us when it is examined?

Answer 8

It tells us, the deeper the ice, the older the air, so examining air in different layers shows us how it’s changed.