Radio dating techniques
Because the ratio of carbon 12 to carbon 14 present in all living organisms is the same, and because the decay rate of carbon 14 is constant, the length of time that has passed since an organism has died can be calculated by comparing the ratio of carbon 12 to carbon 14 in its remains to the known ratio in living organisms.In the late 1940s, American chemist Willard Libby developed a method for determining when the death of an organism had occurred.Geologists often need to know the age of material that they find.They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of years.Which illustrates that, contrary to popular belief, the dating methods are not the primary way that ages are decided. Their results are always ‘interpreted’ to agree with other factors, such as the evolutionary interpretation of geology and fossils.A technique for measuring the age of organic remains based on the rate of decay of carbon 14.This is different to relative dating, which only puts geological events in time Most absolute dates for rocks are obtained with radiometric methods.These use radioactive minerals in rocks as geological clocks.
Their result of 212–230 million years did not agree with the age of the fossils (elephant, pig, ape and tools) so they rejected the date.
These rates of decay are known, so if you can measure the proportion of parent and daughter isotopes in rocks now, you can calculate when the rocks were formed.
Because of their unique decay rates, different elements are used for dating different age ranges.
They said the sample was contaminated with excess argon.
Using new samples of feldspar and pumice they ‘reliably dated’ the tuff at 2.61 million years, which agreed nicely.
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So Curtis and others redated the KBS tuff using selected pumice and feldspar samples, and obtained an age of 1.82 million years.