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A new line, the discordia, will plot along a different trajectory, but it will intercept the concordia in two places.The upper intercept will denote the timing of the primary rock-forming event, while the lower intercept will denote the timing of the reheating event.For this reason, three or more grain types or parts of a grain are analyzed to establish that material of only one age is present.Experience with the results of the uranium–lead method for zircons has demonstrated an interesting paradox.Trying to gauge the age of the Earth has a long tradition.James Ussher, the Anglican Archbishop of Armagh and Primate of All Ireland, concluded in 1650 that the moment of creation occurred at nightfall preceding Sunday 23 October 4004BC.Uranium–lead dating relies on the isolation of very high-quality grains or parts of mineral grains that are extremely rare but nevertheless present in most igneous, metamorphic, and sedimentary rock units.

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Geochronologists can separate recent lead loss due to some disturbance event, such as the reheating of the rock, from the normal rate of lead loss by plotting the ratio of lead to uranium in the sample.

Of course, such a high blocking temperature can have its disadvantages.

Inherited cores may give a mixed false age when the age of crystallization is sought.

The dating work on the crystal, which was carried out by a team led by John Valley of the University of Wisconsin-Madison, shows that the Earth’s crust began to form relatively soon after the planet itself came into existence, which would extend the age of the origin of life.

Scientists believe the Earth was created about 4.56 billion years ago.

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