How is relative dating used to evaluate geologic time

Paleomagnetic dating involves the analysis of the magnetic alignment of iron containing minerals within a rock, and is yet another useful tool for dating rocks younger than 100 million years.The Earth’s Magnetic Poles have alternated their polarities many times in the past (changing from North – South to South – North and back).Radioactive or radiometric dating is a very important method of determining an absolute age for a rock using radioactive isotopes.As minerals crystallise in igneous and metamorphic rocks they trap certain isotopes in their crystal structure that begin to decay radioactively as soon as the mineral forms.

The rate at which the isotopes decay is in effect our "geological clock".Archbishop James Ussher of Armagh, Ireland, 1654, added up generations from the Old Testament and determined that Earth formed on October 23, 4004 BCE.The goal of this lecture is come to come to a scientific understanding of geologic time and the age of the Earth.Sedimentary and igneous rocks are often imprinted with the magnetic alignment of the Earth at the time they were formed.The record of these magnetic reversals has itself been studied to create the paleomagnetic time scale, which looks like an irregular bar code.

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