cross-posted from: https://lemmy.dbzer0.com/post/55447421
this post was submitted on 13 Oct 2025
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If Earth has been around 4B years, do that mean there was a relative shitload of uranium when it formed? And that's why lead is so common?
yep
U-235 has a half life of about 700 million years, so it's fair to assume that there's about 1.1% as much U-235 as when the earth formed 4.6 billion years ago (about 6.5 half lives).
Most uranium on earth is U-238, though, which has a longer half life of about 4.5 billion years, so that the amount of U-238 on earth today is about half of when the earth was formed. But the meme is about U-235, so that's just background information not directly relevant to the picture.
OH! I knew U-235 was far more rare, but I was thinking in terms of ALL Uranium decaying at the faster half-life, forgetting the isotopes. Makes more sense now. Thank you!
Nah just lots of stable lead
Yesh