Fossils and geological time

Discovering Geology

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Our planet formed 4.6 billion years ago which, compared with a human lifespan, is almost inconceivably old. Geologists use a number of techniques to determine the age of rocks, for instance:

  • basic field observations: these help work out the relative sequence of geological events, such as the order in which sediments were deposited
  • fossils: because species evolve and become extinct, fossils of some plants and animals are confined to known, specific periods of geological time
  • radioactive elements: because these elements decay at a known rate, in some circumstances they can be used to calculate how many years have passed since a mineral crystallised or a rock was deposited

By careful accumulation and comparison of this type of information over many years, geologists have constructed detailed timelines and timecharts describing the Earth’s history and, every day, new discoveries help to fill in the gaps in our knowledge.

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BGS geological timechart

Geological timechart

The BGS geological timechart provides colourful reference material for use in schools, colleges and at home.

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Ammonite p521007

Fossils

What is a fossil and why do we study them? Explore the different methods of fossil preservation.

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Browse fossil records

ammonite p885148

Ammonites

Find out about ammonites, an extinct ancient relative of octopus, squid and cuttlefish.

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belemnite p521001

Belemnites

Find out about belemnites, an extinct ancient relative of octopus, squid and cuttlefish.

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bivalves p549460

Bivalves

Find out about both modern and extinct bivalves.

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brachiopod p871945

Brachiopods

Find out about ancient brachiopods and their descendants that live in today’s oceans and seas.

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coral p549521

Corals

Find out about corals, tiny marine animals related to sea anemones that can build huge reefs.

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