Uranium 238 dating rocks

Posted by / 28-Jan-2017 19:08

Uranium 238 dating rocks

Bowen also demonstrated that if a mineral remained in the melt after it had crystallized, it would react with the remaining melt and produce the next mineral in the sequence shown in Figure 3.6.For this reason, this arrangement of minerals became known as Bowen's reaction series.Ordinarily, these reactions are not complete so that various amounts of each of these minerals may exist at any given time.The right branch of the reaction series is a continuum in which the earliest formed calcium-rich feldspar crystals react with the sodium ions contained in the melt to become progressively more sodium rich.To me it has been a real eye opener to see all the processes that are taking place and their potential influence on radiometric dating.Radiometric dating is largely done on rock that has formed from solidified lava.During the last stage of crystallization, after most of the magma has solidified, the remaining melt will form the minerals quartz, muscovite mica, and potassium feldspar.Although these minerals crystallize in the order shown, this sequence is not a true reaction series.

This reaction will continue until the last mineral in the series, biotite mica, is formed.

Geologists assert that older dates are found deeper down in the geologic column, which they take as evidence that radiometric dating is giving true ages, since it is apparent that rocks that are deeper must be older.

But even if it is true that older radiometric dates are found lower down in the geologic column, which is open to question, this can potentially be explained by processes occurring in magma chambers which cause the lava erupting earlier to appear older than the lava erupting later.

The general idea is that many different minerals are formed, which differ from one another in composition, even though they come from the same magma.

The mineral makeup of an igneous rock is ultimately determined by the chemical composition of the magma from which it crystallized.

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Such a large variety of igneous rocks exists that it is logical to assume an equally large variety of magmas must also exist.

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