Lesson video

Hello, I'm Mrs. Adcock, and welcome to today's lesson on formation of fossil fuels.

We are going to be thinking about what are fossil fuels and how are they formed.

Today's lesson outcome is, "I can describe what coal, oil and natural gas are, how they are formed, and why they are non-renewable energy resources." Some of the keywords that we will be using in today's lesson include hydrocarbons, organic matter, plankton, decomposition, and fossil fuel.

Here you can see each of those keywords written in a sentence.

It'll be a good idea to pause the video here and read through those sentences.

You might even like to make some notes so that you can refer back to those later in the lesson if needed.

Today's lesson on formation of fossil fuels is split into two parts.

First of all, we're going to look at coal and then we're going to move on to look at crude oil and natural gas.

Coal, crude oil, and natural gas are all fossil fuels.

Let's get started, looking at coal.

Coal is a black, sedimentary rock that is composed mostly of carbon and hydrocarbons.

What are hydrocarbons? Hydrocarbons are molecules containing hydrogen and carbon atoms only.

An example of a hydrocarbon is shown here.

We can see that this molecule contains two carbon atoms and six hydrogen atoms, and it only contains carbon and hydrogen atoms. It's known as a hydrocarbon.

Coal contains mostly carbon and hydrocarbons, but it may contain low amounts of impurities such as sulphur.

Time for a check for understanding.

Coal contains hydrocarbons.

Which of the following are hydrocarbons? The correct answers are A and C.

A and C are both hydrocarbons.

They are molecules made up of hydrogen and carbon atoms only.

B is not a hydrocarbon, because it contains a sulphur atom.

True or false? Coal may contain impurities.

That statement is true.

Let's see if you can justify your answer.

Is it true because coal consists of mainly carbon and hydrocarbons, but contains impurities such as sulphur, or B, coal consists of mainly sulphur and hydrocarbons, but contains impurities such as carbon? Now both of those statements are very similar, so read them carefully and see if you can identify the correct one.

The correct answer is A, coal consists of mainly carbon and hydrocarbons, but can contain impurities such as sulphur.

Well done if you got that one correct.

Coal forms over millions of years from dead trees and other plants.

About 300 million years ago, during the Carboniferous period, the Earth was covered in swampy forests.

And we can see a picture of a swampy forest on Earth nowadays.

What happened to the plants that died in these swampy environments about 300 million years ago? The dead plants became buried under layers of plant material and mud.

The conditions were anaerobic.

Anaerobic means without oxygen.

The conditions were anaerobic, which slowed down the rate of decomposition, so most of the carbon was retained.

Decomposition is the breakdown of dead and decaying matter.

These conditions, along with high temperatures and high pressure, led to the formation of peat.

There's an image there showing some peat.

What is peat? Peat is a material made of partially decomposed organic matter, largely plant material, from waterlogged environments such as swamps.

So we saw that swampy environment and when dead plants and animals died, then those anaerobic conditions and high pressure and high temperature led to the formation of peat.

Peat can be dried and used as a fuel.

It's used in some places for heating, to cook food, and to generate small amounts of electricity.

The layers of dead plants and sediment that formed peat, continue to experience high pressures from the weight of the material above, and high temperatures from Earth.

And this continued heat and pressure turns this peat into hard, carbon-rich coal.

And there's an image there showing that black sedimentary rock that's coal.

Time for another check for understanding.

High temperatures and low pressure cause peat to turn into coal.

Is this statement true or false? That statement is false.

Hopefully you were able to identify that.

Let's see if you can now justify why that is a false statement.

Is it A, because high temperatures and high pressure cause peat to turn into coal, or B, low temperatures and low pressure cause peat to turn into coal? The correct answer is A, high temperatures and high pressure cause the peat to turn into coal.

Well done if you got that correct, you're doing really well so far.

What is coal made from? Is it made from A, plankton, B, plants, C, crude oil? The correct answer is plants.

Well done if you got that correct, you're clearly focusing well in today's lesson.

It's time for our first practise task of today's lesson, and what you need to do is arrange the following statements into the correct order to describe how coal is formed.

If you pause the video now, read through those statements, arrange them into the correct order to describe how coal is formed, and then come back when you're ready to go over the answers.

Welcome back.

Let's see if you managed to arrange those statements into the correct order.

Firstly, plants living in swampy forests die.

The plants are covered in layers of mud and additional dead plants.

Anaerobic conditions, and just remember that means without oxygen, along with high temperatures and high pressure, turn the dead plants into peat.

Further high temperatures from the Earth and high pressures from the weight of the material above turn the peat into carbon-rich coal.

Hopefully you got those in the correct order.

Well done if you did.

We have looked at how coal was formed, and now we're going to move on to have a look at crude oil and natural gas.

Millions of years ago, dead plankton settled at the bottom of the oceans.

Plankton are microscopic, aquatic, that means they live in water, plants and animals.

And there's two main types of plankton.

They are phytoplankton, which are plants, and zooplankton, which are animals.

These plankton that died and settled at the bottom of the ocean, were covered in layers of mud and other sediment.

We've got an image there where we can see the ocean floor and then we've got the dead plankton and sediments and mud forming layers, and then at the top can see the water.

Time for a check for understanding.

What are plankton? Are they A, microscopic aquatic, plants and animals? B, microscopic land animals, or C, macroscopic plants and animals? The correct answer is A, plankton are microscopic, aquatic plants and animals, and microscopic means they are only visible with a microscope.

High pressure from sediments and rocks above and high temperatures from the Earth turned the dead plankton into crude oil and natural gas.

Here we've got an image, and you can see we've got the dead plankton that form crude oil and natural gas, and these are present in sedimentary rocks, and above them are other layers of sedimentary rock.

Here's an image to show you what crude oil looks like.

You can see it's a thick, black liquid.

Crude oil and natural gas are found in the pores, so little holes, in sedimentary rocks.

They move through the sedimentary rock, moving through those pores, until they reach impermeable rock.

And this impermeable rock they're not able to pass through.

So what happens is the crude oil and natural gas, they move through the sedimentary rock, through those pores, and then they gather in little reservoirs below the impermeable rock.

It says there at the bottom reservoirs of crude oil and natural gas form below the impermeable rock.

We can see an image here where we've got a crude oil reservoir and a natural gas reservoir, and they are in the pores of sedimentary rocks, but they are trapped below that impermeable rock.

To extract crude oil and natural gas, companies drill down through the impermeable rock to the crude oil and natural gas reservoirs below.

Here you can see a land drilling rig and an offshore drilling rig, and both of these drill down through the impermeable rock to extract that crude oil and natural gas.

Coal, that we looked at earlier, and crude oil and natural gas are all fossil fuels, so they are fuels that are made from dead plants and animals over millions of years.

The organic matter that forms crude oil and natural gas decomposes into hydrocarbons.

Organic matter is material that has come from living organisms. So like coal, both crude oil and natural gas contain large amounts of hydrocarbons.

And hydrocarbons were those molecules that were made of hydrogen and carbon atoms only.

Hydrocarbons can react with oxygen in combustion reactions.

And do you know why are the combustion of fossil fuels useful to humans? You might have thought of some of the times when we actually do burn fossil fuels.

So we burn fossil fuels to generate electricity and in vehicles and to cook our food.

But why do we burn those fossil fuels? Well, combustion reactions release large amounts of energy, making coal, crude oil, and natural gas really useful fuels.

Here we've got an image of some burning coal releasing energy.

However, the bad news, fossil fuels will eventually run out as they are non-renewable energy resources.

And this means they are being used at a faster rate than they are produced.

We've already seen today how fossil fuels take millions of years to produce, and yet we are burning large quantities at a really fast rate.

Let's have a go at this question.

What are crude oil and natural gas made from? A, air, B, plankton, or C, trees? Crude oil and natural gas are made from plankton.

Well done If you choose option B.

Here's another true or false question.

Coal, crude oil, and natural gas all contain hydrocarbons.

Is that statement true or false? Yes, well done.

That statement is true.

Can you justify your answer? How did you know that coal, crude oil, and natural gas all contain hydrocarbons? A, the hydrocarbons can react with oxygen in combustion reactions to release energy, or B, the hydrocarbons can react with sulphur in combustion reactions to release energy? It's A, the hydrocarbons can react with oxygen in combustion reactions to release energy.

Well done if you got that one correct.

It's time for our final practise task of today's lesson.

What you need to do is decide if the following statements are true or false.

Once you've read through A to G and decided if they're true or false, you need to make changes to improve any statements that you think are incorrect.

Pause the video now, read through those statements, decide if they're true or false, and make your corrections to any incorrect statements.

Then come back when you're ready to go over the answers.

Let's see how you got on.

A, coal is made from plankton and mainly contains carbon.

That one is false.

Coal is made from plants and mainly contains carbon.

It's crude oil and natural gas that are made from plankton.

B, Coal is a combustible, sedimentary rock.

That statement is true.

We've just looked at how we can burn coal, natural gas and crude oil by reacting them with oxygen to release large amounts of energy.

C, coal may contain impurities such as sulphur.

That is another true statement.

D, natural gas and crude oil are made from plankton.

That one's also true.

E, natural gas and crude oil do not contain hydrocarbons.

That statement is false.

Natural gas and crude oil do contain hydrocarbons.

And remember, coal also contains hydrocarbons.

F, natural gas is formed from phytoplankton and crude oil is formed from zooplankton.

That statement is false, because it suggests that only phytoplankton make natural gas and that crude oil is made from only zooplankton.

However, we know natural gas and crude oil are formed from plankton, and that can include phytoplankton and zooplankton.

G, coal, crude oil, and natural gas are renewable resources.

That statement is false.

Coal, crude oil, and natural gas are non-renewable resources, because they are being used at a faster rate than they are produced.

Well done if you identify correctly which of those statements were true and which ones were false, and if you were able to make improvements to any incorrect statements.

We've reached the end of today's lesson on formation of fossil fuels.

You've worked really hard.

Let's just summarise some of the key points that we've covered in today's lesson.

Coal is a combustible, sedimentary rock, because it is made mostly of carbon.

It does contain hydrocarbons and it's got some impurities such as sulphur.

Coal is formed from deep sediments of organic matter made of prehistoric plants.

Oil and gas are formed from dead plankton mixed in with sediments that formed millions of years ago.

Oil and natural gas are found in pores of sedimentary rock, and we saw how they formed reservoirs underneath the impermeable rock.

The organic matter that formed coal, oil, and natural gas decomposed into hydrocarbons.

You have been super in today's lesson.

I've really enjoyed it and I hope you have too, and I hope you're able to join me for another lesson soon.