The Changing Earth

How do we know that the climate has changed?

In more recent times, geologists and paleontologists have been able to make more accurate measurements of the age of ancient rocks. Trees produce a new ‘ring’ every year, and these can be measured and counted. The width of the ring shows how well the tree grew in any year, reflecting climatic conditions at that time. The rings of even partly fossilized trees buried in bogs can be measured, and these measurements provide accurate records of climate changes over the past 750,000 years. By measuring the radioactivity of once living material, scientists can make accurate measurements up to 40,000 years ago. 

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How was oil formed?

Most scientists think that oil was formed from the remains of tiny plants and animals that inhabited the seas millions of years ago. When these creatures died, their remains were buried in layers of rock. Substances in their bodies gradually altered to form oil. Other scientists disagree, and believe that oil formed from carbon-containing materials that were trapped inside the rock when the Earth was formed. Oil is found in rocks buried beneath the continents, and beneath the shallow parts of the oceans. More than half of the world’s known oil resources are in the Middle East. 

Picture credit: google


How oil is formed?

Oil is a fossil fuel. It is made from the remains of tiny plants and animals called plankton. The plankton lived in the seas when dinosaurs still ruled the world. Over millions of years the tiny plants and animals have changed into oil.


These tiny planktons float in the sea.

Tiny plankton living in our seas today is similar to the prehistoric plankton from which oil is made. Like today’s plant plankton, the tiny prehistoric plants used energy from sunlight to make their food. When they were eaten by animal plankton, the Sun’s energy passed into the tiny animals. So, oil made from prehistoric plankton is actually stored from the Sun.




It takes millions of years for oil to form.

  1. Millions of years ago plankton died and fell to the seabed.

  2. Layers of dead plants and animals built up on to the seabed.

  3. Mud and sand (sediment) sank to the bottom of the sea and covered these layers of plankton.

  4. More layers of sediment piled up on top of the dead plankton. The bottom layers were squashed and became hotter.

  5. Slowly the muddy sediment turned into rock.

  6. The plankton rotted, giving off bubbles of gas, and turned into a thick liquid. This is crude oil.

  7. Crude oil and gas seeped up through the spongy rock, until they reached a solid rock. They stayed under the solid rock in a pool or reservoir.

Black gold



Every day millions of people use oil in some way. Yet, it is only in the past 150 years that oil has become so important to so many people. Oil is so valuable that it is sometimes called ‘black gold’. Imagine life without plastic and fuel.







Oil was once used in lamps.

Oil has been used for thousands of years. In places where oil naturally seeped to the surface, people collected it. The Ancient Babylonians used it as a mortar for building. The Native Americans used it as glue. In the 1850s, people decided they would not wait for the oil to come to the surface. They would drill for it.






When cars were invented, more oil was needed.

When the petrol engine was invented the demand for oil grew. Cars became more common. Now, oil has become a vital part of our life. Many oil-fields have been discovered and about 80 million barrels of oil are produced each day.





Wars are fought over oil.

Oil has become so important and valuable that wars have been fought over oil-fields. In 1991, Iraq invaded its neighbour Kuwait because it wanted Kuwait’s oil-fields. The UK and USA went to war with Iraq to help free Kuwait. Many of the oil-fields were deliberately set on fire by the Iraqi soldiers. Burning and leaking oil caused a lot of pollution to the environment.

Finding oil



Oil is very valuable. Geologists, people who study rocks, look for clues that show where oil might be in the ground. They study the shape of hills, the colour of rocks, and the type of soil, to find out if they might contain oil.




This geologist is looking for oil.

Geologists search for rocks that might have oil in them. They can do this by sending sound waves and electric currents through the ground. Geologists can work out where there might be rocks with oil in them by studying how fast the waves and currents travel through the rock.






Rock samples are drilled out of the ground.

If geologists find rocks that could contain oil, they drill a small test well. A sample of rock called a ‘core’ is brought up to the surface. The rock sample is checked for oil. If there is oil in the rock, the geologists will see tiny droplets of oil clinging on to the rock, a bit like drops of water clinging on to a window after a rainstorm.







Oil is found all over the world.

Oil is found in many countries all over the world. It is found on land and under the sea. The Middle East has two thirds of the world’s known oil reserves. The amount of oil in an oil-field is measured in barrels. Saudi Arabia, in the Middle East, has 262 thousand million barrels of oil.

Oil Drilling deep



Drilling rigs are used to drill into the ground to reach oil. The rigs have a flat base called a platform. A tower holds up the drilling equipment. The drill is a steel pipe which has a point at the end. This is called a ‘drill bit’.



Oil-rigs can be built in the sea.

When oil is found under the seabed, an oil-rig is built over the oil-field. Different rigs are used depending on how deep the water is. Oil-rigs with legs are used in water less than 400 m deep. Floating rigs are used in water up to 1,000 m deep. They are tied to blocks on the seabed to stop them drifting away. In even deeper water, rig ships are used, which are kept in place by anchors.





The drill bit cuts down through the rock.

As the drill bit bores deeper into the ground, more lengths of pipe are added at the top. The drill bit is covered with diamond dust. Diamonds are very hard and strong, so they help the drill to grind through the rock.




Drills reach oil deep under the ground.

In many oil-fields, the oil is pressed and squashed deep inside the rock. When a hole is drilled into the rock, the pressure pushes the oil upwards and out. The pressure can last for days or years, but eventually the flow of oil drops. Then, pumps are needed to bring more oil to the surface.