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Radiometric dating human history
Isotope numbers refer to the combined number of protons and neutrons.
Dendrochronology is useful in measuring tree rings from zero to 12,000 years old.
Tree rings from bristlecone pines provide scale for correcting radio-carbon dating.
After another 5,730 years half of the remaining amount of carbon 14 decays to by half again so that only one quarter of the original amount is left, and so on.
Stable atoms remain stable over time while isotopes decay.
Uranium-thorium dating, also called thorium-230 dating or uranium series disequilibrium is useful in measuring minerals, shell, bone, teeth and coral between 0 and 400,000 years old.
The rubidium-strontium method is useful in measuring minerals between 60 million and 4.5 billion years old.[Source: Time magazine, December 18, 2007] Sometimes geologists can help date objects by measuring the amount of rain wear in cracks, alluvial deposits by streams and glaciers and layers of silt in lakes.Lichenometry is useful in measuring lichens from 100 and 9,000 years old.When a material is created or, in the case of organic materials, dies the ratio of stable atoms to isotopes is known.By measuring the change in ratio of isotopes to stable atoms an object can be dated.The geomagnetic polarity timescale method is useful in measuring minerals between 780,000 and 200 million years old in places where there are no volcanic deposits are formed.This method dates objects by measuring the periodic reversals of the north and south magnetic poles, which have occurred at known times and rates.It dates a mineral by measuring the ratio of amount of rubidium and strontium produced by the decay of rubidium.The potassium-argon method is useful in measuring minerals that around the same age.Carbon 14 for example has a half life of 5,730 years.This means that after 5,730 years the amount of carbon 14 in an object is reduced by half.