Kids definition radiometric dating

Scientists know exactly how long it will take for half the quantity of the element to change, and this state is known as its half-life.

These use radioactive minerals in rocks as geological clocks.

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

Radiocarbon dating measures radioactive isotopes in once-living organic material instead of rock, using the decay of carbon-14 to nitrogen-14.

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

A fossil will always be younger than fossils in the beds beneath it and this is called the principle of superposition.

In an undisturbed sequence of rocks, such as in a cliff face, it is easy to get a rough idea of the ages of the individual strata – the oldest lies at the bottom and the youngest lies at the top.

There are some radioactive elements in rock that decay by giving off energy and turning into different, more stable elements.

This radioactive decay takes place at a constant rate for each radioactive element.

Because of their unique decay rates, different elements are used for dating different age ranges.

For example, the decay of potassium-40 to argon-40 is used to date rocks older than 20,000 years, and the decay of uranium-238 to lead-206 is used for rocks older than 1 million years.

The sediment of this area was laid down after ammonite A appeared 199 million years ago, and before ammonite B became extinct 195 million years ago.

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