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More recently, they have developed a number of new methods.
Some use radioactive isotopes; others take advantage of different phenomena, such as thermoluminescence and electron spin resonance.
ESR can be used to evaluate materials up to one million years old and has become an indispensable tool for paleoanthropologists, who often use it to date the teeth of animal remains found among the precious human fossils.
AMINO ACID RACEMIZATION Over time, the amino acids that make up proteins slowly convert from their so-called left-handed state to their right-handed forma phenomenon known as racemization.
When temperature and environment are constant, conversion occurs at a constant rate.
In theory, this should allow researchers to date protein up to 100,000 years old.
Although visual inspection of the rocks, fossils and archaeological remains used to reconstruct our planet's past provides critical information, only by ascertaining their ages can researchers put this data into a meaningful context.Researchers can thus determine the amount of time that has passed since the buried crystal was last exposed to heat.In the case of thermoluminescence, resetting the crystal clock means heating it to around 500 degrees Celsius.Still others, like amino acid racemization, show promise but have not yet taken wing.Now, nearly 100 years after Boltwood's groundbreaking work, it is estimated that Earth formed at least twice as long ago as he had claimed.