Dating the earth
Meanwhile, Arthur Holmes (1890-1964) was finishing up a geology degree at the Imperial College of Science in London where he developed the technique of dating rocks using the uranium-lead method.By applying the technique to his oldest rock, Holmes proposed that the Earth was at least 1.6 billion years old.It can combine with other atoms and molecules such as oxygen to create carbon dioxide, or CO2.Through the process of photosynthesis, plants absorb carbon dioxide which contains C left in a sample to accurately measure without contamination.Since 1955 the estimate for the age of the Earth has been based on the assumption that certain meteorite lead isotope ratios are equivalent to the primordial lead isotope ratios on Earth.In 1972 this assumption was shown to be highly questionable.Carbon-14 is a radioactive isotope formed in the upper atmosphere.It is constantly being produced by a system in which cosmic rays from the sun hit atoms, releasing neutrons. Carbon-14 becomes a part of the mostly homogenous mixture of air in the atmosphere.
The basic theory of radiometric dating is briefly reviewed.
Despite this, the momentum gained in the two decades prior to 1972 has made 4.5 b.y.
a popularly accepted “universal constant” even though the foundations on which it was based have been virtually removed.
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