The composition and evolution of the Earth's atmosphere + Carbon dioxide and methane as greenhouse gases + Common atmospheric pollutants and their sources

For how many years have the proportions of different gases in the atmosphere have been much the same as they are today?

200 million.

What are the approximate proportion of gases in the atmosphere?

• About four-fifths (approximately 80%) nitrogen.

• About one-fifth (approximately 20%) oxygen.

• Small proportions of various other gases, including carbon dioxide, water vapour and noble gases.

Why is evidence for the early atmosphere limited?

Because of the time scale of 4.6 billion years.

What does one theory suggests about the first billion years of the Earth’s existence?

• During the first billion years of the Earth’s existence there was intense volcanic activity that released gases that formed the early atmosphere and water vapour that condensed to form the oceans.

• At the start of this period the Earth’s atmosphere may have been like the atmospheres of Mars and Venus today, consisting of mainly carbon dioxide with little or no oxygen gas.

• Volcanoes also produced nitrogen which gradually built up in the atmosphere and there may have been small proportions of methane and ammonia.

How was carbon dioxide reduced in the atmosphere?

When the oceans formed, carbon dioxide dissolved in the water and carbonates were precipitated producing sediments.

How was oxygen increased in the atmosphere?

Algae and plants produced the oxygen that is now in the atmosphere by photosynthesis.

Algae first produced oxygen about 2.7 billion years ago and soon after this oxygen appeared in the atmosphere. Over the next billion years plants evolved and the percentage of oxygen gradually increased to a level that enabled animals to evolve.

How else did carbon dioxide decrease?

Algae and plants decreased the percentage of carbon dioxide in the atmosphere by photosynthesis. Carbon dioxide was also decreased by the formation of sedimentary rocks and fossil fuels that contain carbon.

What do greenhouse gases in the atmosphere do?

Greenhouse gases in the atmosphere maintain temperatures on Earth high enough to support life. Water vapour, carbon dioxide and methane are greenhouse gases

What does human activity do?

Increase the amounts of greenhouse gases in the atmosphere, including:

• Carbon dioxide

• Methane.

What are examples of human activites that increase the amount of greenhouse gases in the atmosphere?

• Deforestation:

• Burning fossil fuels:

• Agriculture.

• Creating waste.

How does deforestation increase the amount of greenhouse gases in the atmosphere?

Fewer trees means less C0₂ less is removed from the atmosphere via photosynthesis.

How does burning fossil fuels increase the amount of greenhouse gases in the atmosphere?

Carbon that was ‘locked up‘ in these fuels is released as CO_2.

How does agriculture increase the amount of greenhouse gases in the atmosphere?

More farm animals produce more mthane through their digestive processes.

How does creating waste increase the amount of greenhouse gases in the atmosphere?

More landfill sites and more waste waste from agriculture means more CO₂and methane release by the decomposition of waste.

Based on peer-reviewed evidence, what do many scientists believe?

That human activities will cause the temperature of the Earth’s atmosphere to increase at the surface and that this will result in global climate change.

What is an increase in average global temperature is a major cause of?

Climate change.

What are four potential effects of global climate change?

• Polar ice caps melting - causing a rise in sea levels, increased flooding incoastal areas and coastal erosion.

• Changes in rainfall patterns (amount, timing and distribution) may cause certain regions to recieve too much/little water; affecting their ability to produce food.

• The frequency and severity of storms may increase.

• Changes in temperature and amount of water available in a habitat may affect wild species, leading to differences in their distribution.

What is carbon footprint?

The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.

How can a carbon footprint be reduced?

By reducing emissions of carbon dioxide and methane, eg:

• Using renewable energy sources instead of fossil fuels.

• Using more efficient processes to conserve energy and cut waste.

• Governments could tax people or companies based on the amount of greenhouse gases they produce - people would chose to fuel-efficent products.

What is the combustion of fuels?

A major source of atmospheric pollutants. Most fuels, including coal, contain carbon and/or hydrogen and may also contain some sulfur.

What might the gases released into the atmosphere when a fuel is burned include?

Carbon dioxide, water vapour, carbon monoxide, sulfur dioxide and oxides of nitrogen. Solid particles and unburned hydrocarbons may also be released that form particulates in the atmosphere.

How is carbon monoxide produced by burning fuels?

During incomplete combustion of fuels due to there being insufficient oxygen present.

How is soot (carbon particles) produced by burning fuels?

Soot forms as a result of incomplete combustion.

How is sulfur dioxide produced by burning fuels?

Sulfur dioxide is released during the combustion of fossil fuels, such as coal, that contain sulfur impurities - the sulfur in the fuel becomes oxidised

How are oxides of nitrogen produced by burning fuels?

Nitrogen oxides are created from a reaction between the nitrogen and oxygen in the air, caused by the heat of the burnig.

What is carbon monoxide?

Carbon monoxide is a toxic gas. It is colourless and odourless and so is not easily detected.

What do sulfur dioxide and oxides of nitrogen cause?

Respiratory problems in humans and cause acid rain (when these gases mix with clouds they form dilute sulfuric acid which then falls as acid rain). Particulates cause global dimming and health problems for humans.