How was crude oil formed?

Crude oil is an important raw material. We use it to produce fuel for cars, ships and planes, as well as to make plastic. Everywhere crude oil is found today, there was once a sea. Plankton floats in the sea. It is made up of plants and animals, some so small you wouldn’t even be able to see them.

It was already like this 100 million years ago. When these plants and animals died, they sank to the seabed. A layer formed and gradually grew thicker. There was almost no oxygen in the depths, and the dead organisms formed a layer of rotting sludge.

Later, other layers of sand and gravel settled on top. More and more layers pressed down on each other, and the enormous pressure caused temperatures deep underground to rise.

The organic-rich mud became oil and natural gas. The layer in which they formed is called the source rock. From there, they slowly migrated upwards into permeable rock layers. Sometimes they reached the surface, where they spread into the sea and the atmosphere.

But in some places they became trapped beneath an impermeable layer of rock. This is known as an oil trap, because the rock prevented oil and gas from rising any further. This process took several million years.

Oil can still be extracted from the ground in these places and put to use. Only small quantities are extracted in Germany. Much larger quantities are extracted, for example, from beneath the North Sea and in the Arab countries of Saudi Arabia, Iraq, Iran and the states along the Persian Gulf. There are also large oil reserves in the USA, Canada, Mexico, Venezuela, China, Nigeria and Russia.

The amount of crude oil is often measured in barrels. “Barrel” is an English word meaning “cask.” One barrel holds just under 159 litres.

Find out:

What do we use crude oil for?
What was everywhere long ago in places where oil is found today?
What were the layers that settled on the seabed made of?
When were these layers formed?
What formed from these layers because there was no oxygen?
What had to happen for natural gas and oil to form from it?
What is the name of the layer in which petroleum formed?
What kept natural gas and crude oil from rising to the surface?
Where is oil produced today?
What is a “barrel”?