Arial shot looking down onto the fossil site.

Sam: Today this area is rich in coal deposits, but what can this tell us about the past?

Exposed layers of black coal are visible, sandwiched in between other rocks.

Sam: Coal is made up of carbon which comes from organic matter. All living things are made up of organic matter.

Animation. A zoomed in image of a carbon atom. The atoms start to multiply. The camera zooms out to reveal a plant filled swamp 300 million years ago. Some plants die and new ones take their place.

Sam: So when living organisms die, they leave behind a layer rich in carbon, but with lots of impurities. Normally, organic matter breaks down easily. However, if it's buried in conditions with no oxygen, it can form a thick layer of preserved plant matter called peat.

The dead plants build up on the ground and create a thick layer. 100 million years ago the sea level rises over the swamp. Other sediments start to build up on top of the peat. The peat is squeezed underneath the new sediments.

Sam: As new sediments get deposited on top, the pressure and heat cause the peat to undergo chemical reactions. This removes some of the impurities and leaves behind even more carbon rich material called lignite.

The sea level falls and the ground above the lignite is no longer under water. The lignite continues to be squeezed even further.

Sam: With even more heat and pressure, most of the impurities are removed from the lignite. What's left behind is a deposit that is almost pure carbon. That is what we call coal.