Sexchat us free - Isotope preferred dating very old rocks

With 238U the Pb/U ratio grows much more slowly with age, but the idea is the same.

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).

This means that zircon data can tell us not only when a rock formed, but also when significant events occurred during its life.

The oldest zircon yet found dates from 4.4 billion years ago.

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

Unlike any other method, uranium-lead has a natural cross-check built into it that shows when nature has tampered with the evidence.

Clearly visible in the canyon walls are the light-colored granites, such as the Zoroaster Granite, which are stark against the darker, folded strata of the Vishnu Schist and the other metamorphic rock units of the Granite Gorge Metamorphic Suite (see lowest purple and green shading in diagram).

These are former sedimentary and volcanic strata that have been transformed by heat and pressure, possibly during the intense upheavals when the dry land was formed on Day 3 of Creation Week.In some outcrops pillow structures have been preserved, testimony to the basalt lavas having originally erupted and flowed under water onto the Creation Week ocean floor.Metamorphic rocks are not always easy to date using radio-isotopes.Other minerals sometimes used for uranium-lead dating include monazite, titanite and two other zirconium minerals, baddeleyite and zirconolite.However, zircon is so overwhelming a favorite that geologists often just refer to "zircon dating." But even the best geologic methods are imperfect.The two cascades are different—235U becomes 207Pb and 238U becomes 206Pb.

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