Uranium isotopes dating dating a ditzy girl

Geologists, paleontologists and archaeologists have pieced together a fairly detailed account of how Earth and its inhabitants evolved.

But just how do researchers determine the ages of the materials they unearth?

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.

Kate Wong RADIOACTIVE ISOTOPES The premise behind techniques involving the use of radioactive isotopes is straightforward.

The first step toward accurately measuring geologic time came at the turn of the 20th century, when French physicist Henry Becquerel discovered the natural radioactive decay of uranium.

Shortly thereafter, building on related work by Ernest Rutherford, American chemist Bertram Borden Boltwood determined that he could use the predictable decay of radioactive elements such as uranium into other elements to keep track of time.

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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.

U-238 and U-235 (which has 143 neutrons) are the most common isotopes of uranium.

Uranium naturally contains all three isotopes (U-238, U-235 and U-234), and it rarely varies more than 0.01% from the average composition shown in the table below without our intervention.

And last week scientists announced that new dates for an extinction event that claimed most of Australia's large animals show that humans, not the climate, wiped them out.

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.

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