The Earth’s StructureThe Earth is almost a sphere. These are its main layers, starting with the outermost.

1. Crust - relatively thin and rocky2. Mantle - has the properties of a solid, but can flow very slowly3. Outer core - made from liquid nickel and iron4. Inner core - made from solid nickel and iron

The lithosphere consists of the crust and outer part of the mantle.

Plate TectonicsIn 1915, Alfred Wegener said that all the continents were once joined together in one supercontinent, called Pangaea, before drifting apart. He called his theory continental drift. He gave three pieces of evidence to support his theory:

1. The edges of the continents fit together like a jigsaw (such as the west coast of Africa and the east coast of South America).

2. There are similar rocks of the same age on different continents (separated by an ocean).

3. There are similar plant and animal fossils on different continents (separated by an ocean).

Many people didn’t believe his theory at first because he couldn’t explain how the continents moved. However, scientists discovered convection currents in the mantle in the 1960s and these currents caused the movement of the continents.

Wegener’s theory of continental drift was now accepted and has led to the new theory of plate tectonics. This theory states the crust is broken up into pieces called tectonic plates and the plates are moving very slowly. The arrows in the diagram show the direction in which the plates move.

Questions – The Earth’s Structure and Plate Tectonics1. Name the four main layers of the Earth. (4)2. State the name of the large pieces which the crust is broken into. (1)3. How fast are these large pieces moving? (1)4. In 1915, a scientist proposed that all the continents were once joined

together in one supercontinent. Name both the scientist and the supercontinent. (2)

5. What evidence did this person use for his theory? (3)6. His theory was not accepted at first. Why was this? (1)7. His theory was proven to be correct in the 1960s. Why was this? (1)8. What name is given to his theory today? (1)

Tectonic Plate BoundariesWhen plates move apartMagma (molten rock) rises from the mantle to fill the gap. It cools and solidifies as it reaches the surface. New igneous rock is then formed at the boundary. The process repeats itself so the rocks get older as they get further away from the boundary.

This is called a constructive plate boundary as new rock is formed. Earthquakes and volcanoes can happen at this plate boundary.

When plates collideIf two plates collide which are of equal density (e.g. two continental plates) then the rocks are folded and pushed up (deformed) to form mountains. Earthquakes may also occur.

Two plates may collide that are not of equal density – an oceanic plate (D) and continental plate (C). The oceanic plate is denser so it is forced down into the mantle (A) by the continental plate.

The rock heats up under great pressure and the plate partially melts forming magma. The magma rises through the crust and can be forced to the surface, forming a volcano (B). The magma (now called lava) then cools to form new igneous rock.

This is called a destructive plate boundary as rock melts. Earthquakes may also occur.

When plates move past each otherThe plates overcome friction and move suddenly. Earthquakes can occur and faults can form (cracks in the plates). This is called a conservative plate boundary as new rock is not formed and rock does not melt (which means volcanoes are not formed).

The location of earthquakes and active volcanoes can therefore be used to identify plate boundaries as they mainly occur on the boundaries.

Questions – Tectonic Plate Boundaries1. What name is given to molten rock found underneath the Earth’s crust? (1)2. Explain how new rock is formed when two plates move apart. (2)3. Give the name of this type of plate boundary. (1)4. What is the connection between the age of the rock and the distance from

the boundary of the plates? (1)5. If an oceanic plate and continental plate collide, which plate is forced down

into the mantle? Give a reason for your answer. (2)6. Why is this called a destructive plate boundary? (1)7. Why can the location of earthquakes and active volcanoes be used to

identify plate boundaries? (1)

The AtmosphereMany scientists believe that the Earth’s early atmosphere was formed from gases released by volcanoes.

The two main gases released were carbon dioxide (CO2) and water vapour (H2O), as well as smaller amounts of methane (CH4) and ammonia (NH3). This means the original atmosphere contained no oxygen (O2).

As the surface of the Earth cooled over time, the water vapour in the atmosphere condensed and formed the oceans and seas.

The amount of carbon dioxide decreased due to a number of processes, the most important being photosynthesis. This began as green plants evolved, using up carbon dioxide and releasing oxygen into the atmosphere for the first time.

The amount of carbon dioxide also decreased because some of it was used to form carbonate rocks and some was locked into fossil fuels formed millions of years ago.

The ammonia decomposed on reaction with the oxygen to form nitrogen (N2) and hydrogen (H2). The hydrogen escaped our atmosphere but the nitrogen remained.

These changes happened over billions of years and eventually lead to the composition of today’s atmosphere.

The change in the composition of the atmosphere over geological time

The composition of today’s atmosphere

Nitrogen = 78 % Oxygen = 21 % Argon = 0.9 % Carbon dioxide 0.04 % Other gases (including neon) = 0.06 %

The air is therefore a source of nitrogen, oxygen, argon and neon. These gases can be separated because they have different boiling points.

Identification of gases

Oxygen – place a glowing splint in a test tube and the splint relights Carbon dioxide – bubble through limewater and the limewater turns

milky

The composition of the atmosphere hasn’t really changed for millions of years. The amount of carbon dioxide and oxygen in the atmosphere is controlled by the carbon cycle, which involves the following processes.

PhotosynthesisThis process happens in the leaves of green plants. It uses up carbon dioxide and produces oxygen.

Combustion This process is another word for burning. Combusting fuels, such as fossil fuels (coal, natural gas and oil) uses up oxygen and produces carbon dioxide.

Respiration This is how animals and plants get their energy. This process uses up oxygen and produces carbon dioxide.

Questions – The Atmosphere1. Name the two main gases that were released from volcanoes. (2)2. Explain how the oceans and seas formed. (2)3. State what happened to the amount of carbon dioxide in the atmosphere

and give the main reason for this change. (2)4. Apart from the amount of carbon dioxide, state two differences between

the composition of the atmosphere of the original Earth and the Earth today. (2)

5. State the percentages (%) of nitrogen and oxygen in the atmosphere today. (2)

6. Give the test for oxygen gas. (1)7. The carbon cycle is made up of three main processes. Name two of these

processes and describe how each affects the composition of the atmosphere. (4)

Global WarmingCarbon dioxide is a type of greenhouse gas. Greenhouse gases trap some of the heat energy reflected by the Earth’s surface within our atmosphere. This is called the greenhouse effect. This has meant the temperature of the Earth has steadily increased since the last ice age. This is called global warming.

Both the greenhouse effect and global warming are natural processes.

However, some scientists believe that the temperature of the Earth is increasing at an increased rate. This is called “enhanced global warming”.

Proposed reasons for “enhanced global warming”

Over the last 250 years we have been combusting more and more fossil fuels which has resulted in carbon dioxide being produced at an increased rate.

Most scientists agree that it is this increased rate of production of carbon dioxide being released into the atmosphere that has resulted in “enhanced global warming”.

Reasons for combusting more and more fossil fuels include an increase in the number of factories and an increase in the number of cars on the roads.

It is also believed that deforestation (cutting down trees for fuel and to make space) has

also contributed to the increased production of carbon dioxide. The reason for this is because less trees means that less photosynthesis can take place (which would remove carbon dioxide).

Some possible consequences of “enhanced global warming”

Drier and hotter summers, leading to more droughts Increased rainfall, leading to increased flooding Ice caps melting at an increased rate, leading to increased flooding Glaciers melting at an increased rate, leading to increased flooding More intense hurricanes Climate change

Examples of how to reduce the amount of carbon dioxide being produced

1. Travel by public transport, walking, cycling or car sharing. This means less fuel is combusted.

2. Use renewable energy resources to generate electricity instead of fossil fuels, such as solar panels, wind turbines or hydroelectric plants. Renewable energy resources do not produce carbon dioxide.

3. Reduce deforestation or plant more trees. This means more photosynthesis will take place.

4. Use carbon neutral fuels, such as wood. Carbon dioxide is produced when the wood is combusted. However, trees photosynthesis and use up carbon dioxide. This means that the amount of carbon dioxide is kept in balance.

5. Reduce the personal use of electricity at home and in work.

Questions – Global Warming1. Explain what is meant by the greenhouse effect. (1)2. Explain what is meant by global warming. (1)3. Give a reason why we are combusting more and more fossil fuels. (1)4. What gas is being produced at an increased rate? (1)5. Give two consequences of “enhanced global warming”. (2)6. Planting more trees would help to reduce “enhanced global warming”.

Explain why this is true. (2)7. Why is wood a carbon neutral fuel? (3)8. Give one way of how you could reduce the amount of carbon dioxide that

you personally produce. (1)

Acid RainFossil fuels, such as coal, can contain sulfur as an impurity. If these fuels are combusted then the gas sulfur dioxide (SO2) is formed. This can form a solution of sulfuric acid when it reacts with water in the atmosphere. This falls as acid rain (pH 2 to pH 4).

The generation of electricity in power stations, using fossil fuels, is the main source of sulfur dioxide.

Some consequences of acid rain

Damages forests Damages crops Lakes become acidic so fish are killed Increases the speed at which metal objects, such as bridges, corrode Damages buildings made from calcium carbonate (limestone)

Examples of how to reduce the amount of acid being produced

1. Use a fossil fuel that contains less sulfur. This would mean that less sulfur dioxide is emitted or produced when the fuel is combusted.

2. React the sulfur dioxide produced by power stations with limestone before it leaves. Limestone is an alkali and neutralises the acidic sulfur dioxide.

3. Use a technique called sulfur scrubbing. It removes the sulfur dioxide in waste gases from power stations.

The amount of sulfur dioxide emitted in the UK has generally decreased over the last forty years. However, on occasion, it actually increased. This usually happened during a long period of cold weather as more people left the central heating on for longer, which resulted in more electricity being generated and more fuel being combusted.

Questions – Acid Rain1. Explain how acid rain is formed. (3)2. Give a pH value for acid rain. (1)3. What is the main source of sulfur dioxide? (1)4. Give three consequences of acid rain. (3)5. Give an example of how to reduce the amount of acid rain produced and

explain your answer. (2)6. Explain why the amount of sulfur dioxide sometimes increased in the UK.

(2)

Numeracy – Acid RainThe table shows the mass of sulfur dioxide (SO2) emitted in a country during certain years.

Year Mass of SO2 emitted (million tonnes)2005 4.02007 3.52009 3.02011 2.82013 2.52015 2.2

1. Calculate the percentage decrease in SO2 emissions between 2007 and 2011. (3)

2. Calculate the percentage decrease in SO2 emissions between 2013 and 2015. (3)

3. Calculate the percentage decrease in SO2 emissions between 2005 and 2009. (3)

4. The mass of SO2 emitted in 2012 was a 10 % decrease from 2009. Calculate the mass of SO2 emitted in 2012 (in million tonnes). (3)

5. The country’s target is to decrease their SO2 emissions in 2015 by a further 20 %. Calculate this target (in million tonnes). (3)