Scientists use a method known as radioisotope dating or **radioactive** or **radiometric dating** to determine the age of rocks, fossils, etc.

Radioactive atoms decay over time to form new products and once we know the rate of decay we can use them for finding the age of rocks. We typically...

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Scientists use a method known as radioisotope dating or **radioactive** or **radiometric dating** to determine the age of rocks, fossils, etc.

Radioactive atoms decay over time to form new products and once we know the rate of decay we can use them for finding the age of rocks. We typically determine the half life of such elements, which is the time over which the material will decay to half its original content.

The idea is to compare the abundance of daughter products with that of original radioactive material and use it to determine the age. For example, say atom A divides to form B and has a half life of 1 billion years. If we find a 1:1 abundance of A and B in a rock (which contained no B initially), we know that 1 half life has passed and 50% of A has decayed into B and thus, the rock is 1 billion years old.

Hope this helps.