Video: How do we figure out that rocks are billions of years old?

Ars explains: How do we find out how old some rocks are? Click here for transcript.

For our first entry of our new science video series, we looked at some one-of-a-kind hardware that gets things moving at nearly the speed of light. Today, we're going to take a look at a process that takes place all over the world. While it does require some specialized equipment, the equipment is common enough that many universities have their own version. Despite being relatively common, though, we can still learn some amazing things from it.

The subject of this description is radiometric dating, which uses radioactive decay of some elements to figure out how old things are. Putting an age on something may seem fairly mundane, but the simple answers provided by dating can impact a huge range of scientific fields.
Carbon dating helps us understand when cultural artifacts were made and when archeological samples were deposited. It helps us figure out when lost environments flourished. Other isotopes let us go older, figuring out when extinct species lived and when evidence of past climate change was put in place. Deeper back in time, we can work through movements of supercontinents that no longer exist, the formation of the Earth's first rocks, and (using some off-world samples) even the start of the Solar System.
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