atmosphere

Question 1

describe the earth’s early atmosphere

Answer 1

• first billion years of earth’s history, the surface was covered in volcanoes
• this is how early atmosphere was formed
• CO2 levels increased due to volcanic activity, and mostly made up the atmosphere
• volcanic activity also released nitrogen, water vapour and small amounts of methane and ammonia

Question 2

describe phase 2 - 4.4 to 2.7 billion years ago, co2 level decrease

Answer 2

• 4.4 to 2.7 billion years ago carbon dioxide levels decreased because water vapour condensed to form oceans, when the earth’s temperature cooled to below 100°C
• carbon dioxide dissolved in oceans
• carbonates were precipitated, forming sedimentary rocks

Question 3

phase 3 - 2.7 to 1.7 billion years ago

Answer 3

• 2.7 - 1.7 billion years ago, oxygen levels increased and carbon dioxide levels decreased
• algae evolved first 2.7 billion years ago
• green plants evolved over the next 1 billion years due to algae appearing and plants evolving
• this is because algae and plants photosynthesise, taking in and absorbing carbon dioxide and releasing oxygen
• as oxygen levels built up it meant animals could evolve
• carbon dioxide levels also decreased by the formation of sedimentary rocks and fossil fuels, containing carbon

Question 4

how is carbon trapped in fossil fuels and rocks?

Answer 4

• 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

Question 5

describe how crude oil and natural gas are formed?

Answer 5

• from deposits of plankton
• fossil fuels form reservoirs under the seabed when they get trapped in rocks

Question 6

what is coal and how is it formed?

Answer 6

coal is a sedimentary rock made from thick plant deposits

Question 7

what is limestone and how is it formed?

Answer 7

sedimentary rock mostly made of calcium carbonate deposits from the shells and skeletons of marine organisms

Question 8

describe global warming

Answer 8

1. short wavelength radiation from the sun passes through the atmosphere
2. the radiation hits Earth’s surface where some of its energy is absorbed, warming the Earth
3. longer wavelength radiation is reflected back off the earth
4. greenhouse gases in the atmosphere absorb long wavelength radiation, warming the Earth so the temperature increases

Question 9

global warming 4 consequences

Answer 9

ice caps melting: rise in sea levels, increased flooding, loss of habitat
changes in rainfall: how much, when, where, too much can damage crops, lack can cause drought
extreme weather: more storms etc.
extinction of animals: due to loss of habitat