Radiometric dating--the process of determining the age of rocks from the decay of their radioactive elements--has been in widespread use for over half a century.

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Sedimentary rock is made of particles derived from other rocks, so measuring isotopes would date the original rock material, not the sediments they have ended up in.

However, there are radiometric dating methods that can be used on sedimentary rock, including luminescence dating.

Each original isotope, called the parent, gradually decays to form a new isotope, called the daughter.

Each isotope is identified with what is called a ‘mass number’.

The atoms of some chemical elements have different forms, called isotopes.

These break down over time in a process scientists call radioactive decay.

Others measure the subatomic particles that are emitted as an isotope decays.

Some measure the decay of isotopes more indirectly.

Because of the fairly fast decay rate of carbon-14, it can only be used on material up to about 60,000 years old.

Geologists use radiocarbon to date such materials as wood and pollen trapped in sediment, which indicates the date of the sediment itself.

It has become increasingly clear that these radiometric dating techniques agree with each other and as a whole, present a coherent picture in which the Earth was created a very long time ago.