Dating sediment layers

But even he “realized that there probably would be variation”, says Christopher Bronk Ramsey, a geochronologist at the University of Oxford, UK, who led the latest work, published today in Science.

Various geologic, atmospheric and solar processes can influence atmospheric carbon-14 levels.

To determine the ages of these specimens, scientists need an isotope with a very long half-life.

Some of the isotopes used for this purpose are uranium-238, uranium-235 and potassium-40, each of which has a half-life of more than a million years.

Fossils, however, form in sedimentary rock -- sediment quickly covers a dinosaur's body, and the sediment and the bones gradually turn into rock.

But this sediment doesn't typically include the necessary isotopes in measurable amounts.

If you look at a cliff made from sedimentary rock, you’ll notice distinct layers that may even be different colors.

Carbon dating is used to work out the age of organic material — in effect, any living thing.

The technique hinges on carbon-14, a radioactive isotope of the element that, unlike other more stable forms of carbon, decays away at a steady rate.

She will lead efforts to combine the Lake Suigetsu measurements with marine and cave records to come up with a new standard for carbon dating.

The most widely known form of radiometric dating is carbon-14 dating.