Scientific carbon dating

The following summaries offer a quick introduction to some of the dating techniques researchers have been using to explore and reconstruct our planet's past, from 4.5 billion years ago to the present.

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But just how do researchers determine the ages of the materials they unearth?Each isotope has what is known as a half-lifethat is, a period of time in which half of the atoms in a population decay into stable daughter elements.This half-life differs dramatically from isotope to isotope.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.The decay of argon 40 to argon 39, for instance, played a vital role in underscoring the significance of two ancient human skulls unearthed in the Republic of Georgia last summer. Swisher III of the Berkeley Geochronology Center and his colleagues reported, are more than 1.7 million years old, and as such represent the first humans to leave Africa to colonize the rest of the world.Argon dating can also be used to date materials as young as 10,000 years and as old as billions of years.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.Because of that condition, scientists say, the technique is well suited to dating meteoritic impacts, fire-treated stones used by early humans, cooking hearths and old ceramics.Somewhat similar to thermoluminescence, electron spin resonance (ESR) dates crystals, too (although these are found in shells and enamel.) Unlike thermoluminescence, however, this method counts the number of "unpaired spins" of electrons trapped in the crystal, instead of freeing them.


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