Isotope dating method chinese gay dating sites

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).Uranium easily substitutes for zirconium while lead is strongly excluded.This means the clock is truly set at zero when zircon forms.

If you took rocks of all ages and plotted their two Pb/U ratios from their two isotope pairs against each other on a graph, the points would form a beautiful line called a concordia (see the example in the right column). First, its chemical structure likes uranium and hates lead.In a 704-million-year-old rock, 235U is at its half-life and there will be an equal number of 235U and 207Pb atoms (the Pb/U ratio is 1).In a rock twice as old there will be one 235U atom left for every three 207Pb atoms (Pb/U = 3), and so forth.Some zircons are obviously disturbed and can be ignored, while other cases are harder to judge.In these cases, the concordia diagram is a valuable tool.

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