Also I’m amazed by how people don’t seem to understand what half-life is. It’s not the time it takes for an atom to decay. It’s the time it takes for half of the atoms to decay, meaning there will be some U-238 that decay into Ra-226 in just a couple of seconds.

So even if the Earth was created 4000 years ago with uranium but not lead (for some weird reason), some of that lead would have decayed into lead by now.