CC17

Question 1

What did Earth’s early atmosphere mostly consist of?

Answer 1

The earth’s early atmosphere is thought to have been mainly carbon dioxide, with smaller amounts of water vapour and other gases, and little or no oxygen.

Question 2

Where did most of the gases from earth’s early atmosphere come from?

Answer 2

Most gases in earth’s early atmosphere came from volcanoes and volcanic activity. Volcanoes affect the atmosphere by releasing large amounts of some gases, such as carbon dioxide and water vapour, and small amounts of other gases (including nitrogen).

Question 3

When were oceans first formed on earth?

Answer 3

About 4 billion years ago.

Question 4

How were oceans first formed on earth?

Answer 4

About 4 billion years ago, the Earth cooled down. This caused water vapour in the atmosphere to condense to liquid water, which formed the oceans.

Question 5

Was there a lot of oxygen in earth’s early atmosphere and why?

Answer 5

There is a lot of evidence to support the idea that earth’s atmosphere contained little or no oxygen in it. This is because oxygen is not produced by volcanoes.

Question 6

When did evidence of oxygen start to appear and what was it?

Answer 6

About 2.4 billion years ago, rocks containing bands of iron oxide started to form. This oxidation of iron suggests that oxygen levels increased at this time. There is also fossil evidence of microorganisms that may have produced this oxygen. So, scientists think that oxygen from these microorganisms reacted with iron in the early oceans, to produce insoluble iron oxides that formed layers on the seabed.

Question 7

How have carbon dioxide and oxygen levels changed as time has passed?

Answer 7

Over hundreds of millions of years the amount of oxygen has increased and carbon dioxide levels have decreased.

Question 8

How does the ocean hypothesis explain the increase in oxygen levels and decrease of carbon dioxide levels?

Answer 8

As the young earth cooled, water vapour in the atmosphere condensed and formed oceans. Many scientists think that carbon dioxide then dissolved in the oceans, reducing the amount of carbon dioxide in the atmosphere. Sea creatures used this dissolved carbon dioxide to form shells made of calcium carbonate, CaCO₃. This then allowed more carbon dioxide to dissolve in the oceans.

Question 9

How does the photosynthesis hypothesis explain the increase in oxygen levels and decrease of carbon dioxide levels?

Answer 9

Some organisms make energy via photosynthesis. These organisms use up carbon dioxide from the atmosphere and produce oxygen. Some of the earliest photosynthetic organisms were cyanobacteria, which live in shallow waters. These bacteria grow in huge colonies and produce sticky mucus. The mucus traps a layer of sand grains and other sediments. The organisms need to move above the sediment layer in order to get sunlight. Over time, the sediment layers build up to form rocky shapes, called stromatolites. They provide evidence that photosynthetic organisms were living at this time. It is thought that microorganisms like these caused a rise in oxygen levels in the oceans and then the atmosphere.

Question 10

When was there another jump in oxygen levels and why?

Answer 10

Around 500 million years ago, there was another jump in atmospheric oxygen levels as plants evolved.

Question 11

How much of our atmosphere does oxygen make up today?

Answer 11

Today, oxygen makes up around 21% of the earth’s atmosphere.

Question 12

Why is oxygen important in today’s atmosphere?

Answer 12

It is important for aerobic respiration in organisms. It also allows combustion (burning) to happen.

Question 13

What is the test for oxygen?

Answer 13

The test for oxygen is when a pure splint is lighted, if it catches fire very quickly, then there is a lot of oxygen in the atmosphere.

Question 14

How does the greenhouse effect keep the earth warm?

Answer 14

1. Energy is transferred from the sun
2. It reaches the surface and most of the energy is absorbed, causing an increase in temperature
3. Some energy is reflected back into space
4. The warm earth emits energy and some of it is transferred to space
5. Some emitted energy is absorbed by greenhouse gases. When it is re-emitted it can be transferred back to the earth’s surface

Question 15

What evidence is there to support climate change?

Answer 15

Since 1850, there has been a steady increase in the burning of fossil fuels for industry. During this period, carbon dioxide levels have increased. As carbon dioxide levels have risen, so has the average temperature of the earth’s surface. This shows that there is a strong correlation between CO₂ levels and surface temperature.

Question 16

What supports the idea that CO₂ causes a temperature rise?

Answer 16

Scientists have shown in the lab that CO₂ absorbs infrared. Satellite data confirm that as CO₂ levels have increased, there has been a reduction of infrared waves from the earth leaving the atmosphere. This supports the idea that CO₂ causes temperature rises because it shows how it could occur.

Question 17

What is a casual link?

Answer 17

One thing causes another.

Question 18

How can the evidence of change of carbon dioxide levels be evaluated?

Answer 18

The amount of carbon dioxide in the air today is measured at monitoring stations around the world. Evidence for historical carbon dioxide levels comes from measuring concentrations of the gas trapped in ice cores.

Question 19

How can the evidence of change of temperature be evaluated?

Answer 19

Today, we use thermometers to measure temperature. Modern thermometers are less prone to error and have greater resolution. Today, we can also analyse huge amounts of data from around the world, including temperature measurements from sources such as censors and satellites.

Question 20

What is causing global warming?

Answer 20

The increased burning of fossil fuels has released more carbon dioxide (CO₂) into the atmosphere, which is thought to be causing global warming. Methane is also being released into the atmosphere and causing global warming.

Question 21

Why is Methane more powerful greenhouse gas than carbon dioxide?

Answer 21

Methane (CH₄) is a more powerful greenhouse gas than carbon dioxide because it is much better at absorbing infrared radiation from the earth.

Question 22

How is Methane produced?

Answer 22

1. Methane is released into the atmosphere when oil and natural gas are extracted from the ground and processed.
2. Livestock farming (especially cattle) also produces a lot of methane. Cattle have bacteria in their stomach to digest tough grass. Some of the bacteria produces methane.

Question 23

What are some effects of climate change?

Answer 23

1. Rising average temperature will cause ice at the South Pole and glaciers to melt. The extra water will raise sea levels, which will lead to increased flooding in some areas.
2. Some animals may move away from their natural habitats to find cooler areas. Some animals may become extinct if they cannot survive at warmer temperatures or find new places to live.
3. As weather patterns change, some areas will become drier and others will become wetter. Scientists predict that there will be more extreme weather events (such as heavy rainfall, powerful storms and heat waves).
4. As more carbon dioxide is released, more of the acidic gas will dissolve in sea water, lowering its pH. This can harm organisms living in the seas and oceans. Additionally, as ocean temperatures rise, it causes coral to push out the photosynthetic algae that live in their tissues. These algae provide the color of coral and so coral ‘bleaching’ may occur. If coral remain ‘bleached’ for too long, they can die.

Question 24

How can greenhouse gas emissions be reduced?

Answer 24

1. Using renewable energy resources can reduce greenhouse gas emissions, but there is a risk that this may not be enough to mitigate (lessen) the effects of climate change that we are seeing.
2. Some have suggested global engineering solutions, to reflect sunlight back into space or to capture CO₂ from the air and bury it underground. However, all countries will need to work together to reduce emissions and help pay for large-scale engineering. There is a risk that some countries will not help and that delicate ecosystems may be disrupted.
3. Helping local people to adapt to new conditions. This includes building flood defences, dams and irrigation systems. However, these ideas may destroy important habitats so there is a risk they may not work.