How are scientists able to tell how old a rock is?
In: Chemistry
Radiometric dating is one of the best methods. Rocks can incorporate certain elements into their crystal structures when they form while rejecting others. For example Zircon can incorporate uranium atoms but strongly rejects lead atoms when it forms.
However once the rock has formed its crystal structure has effectively set, uranium is radioactive and so over time it will decay down to lead (with a half life of hundreds of millions to billions of years). Any lead in zircon must have been formed from uranium which has decayed because it couldn’t have been there when the rock formed. This means that by measuring the amount of lead compared to the amount of uranium you can work out how long the rock has been solid for, i.e its age.
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