U 238 dating rocks
But now imagine that some geologic event disturbs things to make the lead escape.
That would take the zircons on a straight line back to zero on the concordia diagram.
It occurs naturally as U-238 with a very small amount of U-235, when U-235 is refined out it is called depleted… Yes, it is used but the rest of the above answer is entirely wrong. Uranium's standard isotope (which is U-238) is composed of 92 Protons ( charges) and 146 Protons (- charges).
This tells you that a standard Uranium atom is negatively charged.
The 235U–207Pb cascade has a half-life of 704 million years and the 238U–206Pb cascade is considerably slower, with a half-life of 4.47 billion years.
So when a mineral grain forms (specifically, when it first cools below its trapping temperature), it effectively sets the uranium-lead "clock" to zero.
Uranium-238, which makes up 99.3% of natural uranium, is not fissionable by slow neutrons.
Unlike any other method, uranium-lead has a natural cross-check built into it that shows when nature has tampered with the evidence.
Uranium comes in two common isotopes with atomic weights of 235 and 238 (we'll call them 235U and 238U).
Both are unstable and radioactive, shedding nuclear particles in a cascade that doesn't stop until they become lead (Pb).
These atoms decay, and from the amount of atoms remaining, an estimate of the…
U-238 is not fissile, therefore it does not produce nuclear power in a reactor, only U-235 does that.The two cascades are different—235U becomes 207Pb and 238U becomes 206Pb.