But all they did, he said, was give the age of a sediment layer.

In doing so it was possible to establish three specific sediment layers.

Newer layers of sediment were added to the old ones.

People used to think the old sediment layers would be the best place to look for traces of ancient life.

At this point the layer of sediment is up to 2 km thick.

In some places the sediment layer is 6,000 feet (1,800 m) thick.

Flowing water appears to have deposited the sediment layers higher up.

Fossilised fish and plant remains are found between the layers of sediment.

It shows layers of sediment that might indicate deposition by a liquid.

Its contents looked inky-red, with a deep layer of sediment at the base.