I’ve never understood how we know how much of a material we had to then calculate it would decay x amount in y years and estimate the approsximate ago.
I know for carbon based things we can compare to how much the atmosphere had of each element and we see the smaple and compare to that “starting point” as an anchor and do the calculations. For rocks however I don’t understand how we get a starting point.
For example lets say we have Uranium chunk that was made from the first exploding start billions of years ago. That chunk after it’s created is flying around decaying. Then a billion years later gets caught up and starts to become part of a new star. That same chunk keeps decaying now in a star and then that start blows up and some of that volume is replaced by new formed Uranium
That chunk now has uranium that decayed mixed with new so when you look at it how would you know how much of the decay is from one starting point vs 2 like in this example or if we extrapoloate down to that chunk going through more events down the line. Then forming as part of the earth. Then we come along and pick it up and saying ahh it has x amount of dacayed downsstream elements so it must have started as Y amount Z years ago.
But how would you know what that chunk your holding went through and what time periods that rock is a combination of from the start of the universes to now in your hand.
In: Chemistry
The first part of the video explains exactly your question: https://youtu.be/UdZfHg2VG5M?si=JAwxhua00jnfXMWU
Basically we know the type of decay uranium 238 undergoes, alpha decay. In the case of uranium 238, this means it releases a helium neutron and becomes thorium 234. Therefore if you had a set amount of uranium 238, and calculated how often helium neutrons are released, you can then calculate the half life.
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