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Define uranium lead dating

This commonly occurs if the system has been heated or otherwise disturbed, causing a loss of some of the lead daughter atoms.

Because Pb are chemically identical, they are usually lost in the same proportions. Wetherill has shown that the two points on the Concordia curve intersected by this straight line will represent the time of initial crystallization and the time of the subsequent lead loss.

Of all the isotopic dating methods in use today, the uranium-lead method is the oldest and, when done carefully, the most reliable.

What makes this fact useful is that they occur at different rates, as expressed in their half-lives (the time it takes for half the atoms to decay).

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.

These ratios can be plotted to produce a curve, the Concordia curve (see concordia diagram).

If the ages determined using these two methods do not agree, then they do not fall on this curve and are therefore discordant.

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