If uranium-238 is formed in a star (supernova), how can it be used to date the age of the earth? Aren’t you dating the age of the supernova? What about earth’s formation creates a marker that can be dated with isotopes?

Question

So how do you get 4.5 billion years by dating isotopes that existed long before the formation of the earth?

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Edit: I’m not creationist trolling. I believe the #, just trying to learn about the sicence.

In: 180

Answer 1

Uranium decays into lead. Zircon is a crystal that incorporates uranium but excludes lead. So, when a zircon crystal is formed you can be sure that the amount of lead is 0%. The only lead in a zircon crystal comes from the uranium decay.

Edit: I should also say that the dating technique uses the ratio of lead to uranium to measure time. No lead corresponds to t = 0.