Relative dating of fossils is based on what

It is possible to calculate the age of a sample by measuring the uranium content and the density of the fission tracks.

The age of volcanic rocks and ash can be determined by measuring the proportions of argon (in the form of argon-40) and radioactive potassium within them.

Accurate dates also allow us to create sequences of evolutionary change and work out when species appeared or became extinct. These are: Where possible, several different methods are used and each method is repeated to confirm the results obtained and improve accuracy.

Different methods have their own limitations, especially with regard to the age range they can measure and the substances they can date.

Uranium is present in many different rocks and minerals, usually in the form of uranium-238.

Argon is gas that gradually builds up within rocks from the decay of radioactive potassium.It is initially formed in the molten rock that lies beneath the Earth’s crust.The heat from a volcanic eruption releases all the argon from the molten rock and disperses it into the atmosphere.Volcanic rocks – such as tuff and basalt – can be used in dating because they are formed at a particular moment in time, during an eruption.Sedimentary rocks are rarely useful for dating because they are made up of bits of older rocks.

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