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

A big part of the answer is that we do date those supernovae. We know when they happened, then how long from that until the earth formed, and on down.

We have to standardize our “earth numbers” to that of our solar systems standard by looking at very, very ancient mediorites. So we are effectively measuring from the age of those super nova for some systems, from the age of zircon formation for some others, from when things melted or got metamorphosed etc.

But all of this depends on having standards for these numbers. How much uranium? How much thorium or lead? That’s where we compare those levels to the solar system baseline.

For many systems, it’s less about the absolute amounts of an isotope, but about the ratios. So you set “this is how much there should be in the solar system” as zero, so the age of those super nova don’t matter, just how much is left over to now.

Again, this all depends on the system and there are a lot of different chemistries going on in geochemistry.