Chemistry - The Earth and the Atmosphere

This is for an AQA GCSE paper and has 5 sub - sub topics:

1. The structure of the Earth          2. Continental Drift          3. The Atmosphere Today          4. The Changing Atmosphere                  5. Carbon Dioxide and Global Warming

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The Structure of the Earth - Beyond the Crust

In the Earth there is the core, - made up of mostly molten iron - the mantle - flowing solid rock because some parts have melted - and the crust - a thin layer of solid - and the atmosphere - layer of gases.

The lithosphere is the top half of the mantle and crust and is broken up into tectonic plates which moves a few centre metres each year.

This is because there is radio active decay which cause heat released causing convection currents. The rock in the mantle heats up, becomes less dense and rises. It is pushed to the sides by more rocks where it cools, making it more dense and sinking back down.The sideways movement of the rocks move the plates.

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The Structure of the Earth - Volcanoes and Earthqu

Volcanoes are the result of tectonic plates moving, under, over or apart from each other and magma escaping from the mantle.

Earthquakes are the result of sudden jerks of tectonic plates caused by their friction. 

We can predict an Earthquake when there are small shocks that only scientific instruments can pick up, water levels fall in wells and some animals act strangley.

Volcano signs are more definite, the signs are increase of temperature of volcano because of magma mooving, rise ground level due to build up of magma and move sulphur dioxide released.

However, these predictions may not be accurate because the magma is too hot to measure. If there was a false prediction and people were evacuated, this would cause disruption and economic loss.

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Continental Drift

Scientists used to thik that the Earth was cooling and when it did the crust shrank and wrinkled forming mountains.

In 1911, Alfred Wegener saw that identical fossils were found in South America and Africa with creatures that could not swim.Wegener came up with the theory of continental drift.

His evidence was, the continents fitted like a jigsaw puzzle, Africa and South America had the same types of rock layers and fossils, there could not have been a peice of land connecting South America and Africa meaning they must have been joined.

Wegener died with his idea unaccepted. This was partly because he was known as a meteorologist and less credited amongst geologists.  

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The Atmosphere Today

As you go further froom the Earth's surface there are fewer gas particles.

The air is mde up of aproximately 78% of nitrogen, 21% of oxygen, 0.9% of argon and 0.04% of carbon dioxide.

Nitrogen can be used for food packaging, oxygen is used to help patiets breath in hospitals and argon is used as a non-reacive metal when welding.

Gases in the air are separating useing fractional distillation and cooling them until they become liquids at -200 degrees.

The gases are then heated and they all have different boiling points so can be collected at different times.

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The Changing Atmosphere

Earth's atmosphere is very different now than when the Earth was first formed.

Some scientist believed theat the gases were formed from the gases given off in volcanoes and some think they came from comets colliding with the Earth.

Many scientists think the early atmosphere contained mainly carbon dioxide, water vapour, ammonia and methane. As the Earth cooled, the water vapour is thought to condense to form oceans.

Scientists are led to believe that there were little or no oxygen in the early atmosphere because volcanoes do not give oxygen and there are rock compounds that can only form with the absence of oxygen.

The increase of oxygen would have occoured when photosyntheising plants produced oxygen from photosyntheis reducing carbon dioxide levels. Carbon dioxide may have also decreased when locked in rocks such as limestone.

The rection with oxygen and ammonia would have increased the amount of nitrogen but there are many other theories.

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Carbon Dioxide and Global Warming

Levels of carbon dioxide are increasing and are thought to cause global warming.

Carbon dioxide used to be the main gas of the Earth. Some carbon dioxide reacted with substances in the sea water forming sedimentary rock.

Some carbon dioxide is also used for algae and plant for photosynthesis. As the plants died, when they decayed they foormed fossil fuels.

Carbon can also be locked up in coal and hydrocarbons that release CO2 when burnt.

Carbon dioxide is a greenhouse gas which keeps the heat from escaping.

Global warming could lead to climate change and floods due to rise of sea levels.

The ocean has a pH of 8 and when carbon dissolves iin the ocean it forms carbonic acid. As carbon dioxide levels increse, sea pH levels decrease. This will dissolve carbonates that many organisms need to make shells or skeletons, and some may not be able to survive without this.

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