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The dating game
by Diane Boudreau
Clues come in many forms. Finding the element rhenium in a core sample taken from Hamersley Basin in Western Australia is important. ASU biogeochemist Ariel Anbar says the find provided scientists with evidence that there was O2 in Earth's ancient atmosphere. But the finding was a stroke of luck for another reason as well. It allowed the researchers to accurately date the rock samples.
One of the isotopes of rhenium is radioactive. It decays into an isotope of osmium. As the rock grows older, the amount of the rhenium "parent" isotope decreases while the amount of the osmium "daughter" isotope increases. Scientists know the rate at which rhenium decays. As a result, they can determine the age of a sample by measuring the amounts of these isotopes.
Dating techniques using radioactive materials (such as carbon dating) are quite common. But few of those techniques are useful in dating sedimentary rocks, says Anbar. Rhenium dating is one that works well.
What have scientists learned from this ancient rock sample? Read more in "Get a whiff of this."
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