Mt st helens radioactive dating
As the crystallization process continues, the composition of the melt (liquid portion of a magma, excluding any solid material continually changes.For example, at the stage when about 50 percent of the magma has solidified, the melt will be greatly depleted in iron, magnesium, and calcium, because these elements are found in the earliest formed minerals.Lava erupting earlier would come from the top of the magma chamber, and lava erupting later would come from lower down.A number of processes could cause the parent substance to be depleted at the top of the magma chamber, or the daughter product to be enriched, both of which would cause the lava erupting earlier to appear very old according to radiometric dating, and lava erupting later to appear younger.Lava (properly called magma before it erupts) fills large underground chambers called magma chambers.Most people are not aware of the many processes that take place in lava before it erupts and as it solidifies, processes that can have a tremendous influence on daughter to parent ratios.This left branch is called a discontinuous reaction series because each mineral has a different crystalline structure.Recall that olivine is composed of a single tetrahedra and that the other minerals in this sequence are composed of single chains, double chains, and sheet structures, respectively.
This belief in long ages for the earth and the existence of life is derived largely from radiometric dating.
The following quote from The Earth: An Introduction to Physical Geology by Tarbuck & Lutgens, pp.
55-57, (1987), gives us an idea of the tremendous complexity of the processes that occur when magma solidifies.
Oftentimes the rate of cooling occurs rapidly enough to prohibit the complete transformation of calcium-rich feldspar into sodium-rich feldspar.
In these instances, the feldspar crystals will have calcium-rich interiors surrounded by zones that are progressively richer in sodium.