Uranium dating zircon
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.
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.
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.
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.
The dating confirmed that the horse does indeed date back 1,000 years to the Tang dynasty, as its style suggests.
Many crystals, including diamond, quartz and feldspar, accumulate and trap electric charges at a known rate over time.
Kate Wong RADIOACTIVE ISOTOPES The premise behind techniques involving the use of radioactive isotopes is straightforward.
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.
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.Some use radioactive isotopes; others take advantage of different phenomena, such as thermoluminescence and electron spin resonance.Still others, like amino acid racemization, show promise but have not yet taken wing.In the decades that followed, scientists made important new discoveries about the structure and behavior of atoms, and they refined their existing dating techniques.
More recently, they have developed a number of new methods.
Argon dating can also be used to date materials as young as 10,000 years and as old as billions of years.