February 26th, 2014
A tiny zircon crystal that scientists say is 4.4 billion years old may help unlock the mysteries of how the Earth first formed.
Discovered in Western Australia’s remote Jack Hills region and barely the size of a grain of sand, the zircon crystal is being touted as the oldest known material on Earth by scientists at the University of Wisconsin-Madison.
John Valley, a professor of geoscience, and his team revealed in the journal Nature Geoscience that the translucent red zircon was nearly as old as the Earth itself. (The microscopic image on this page shows the red zircon glowing blue when bombarded by electrons.)
Scientists believe the Earth and the rest of the solar system were formed 4.567 billion years ago. The discovery of the ancient zircon crystal gives scientists good reason to believe that a once-molten Earth cooled quickly and solidified at least 4.4 billion years ago. The Earth's crust — including the tiny Aussie zircon — took shape only 160 million years after the creation of the solar system, the scientists reported.
Zircon is particularly precious to scientists because zircon crystals can withstand billions of years of abuse, explained Carl Zimmer in an article for National Geographic.
“Zircons have the added attraction of holding onto radioactive isotopes such as uranium. Over billions of years, the uranium decays at a steady rate into lead. By measuring the atoms of uranium and lead in a zircon, scientists can get a tight estimate of the zircon’s age,” he wrote.
Valley and his team used two techniques to confirm the zircon’s age. The first measured how many radioactive uranium atoms in the crystal had decayed into lead. The half-life of uranium-238 is about 4.47 billion years.
A second method, called atom-probe tomography, was used to count individual atoms of lead in the crystal and to determine their mass.
The scientists say the crystal's chemistry, which includes oxygen isotopes, suggests that the temperatures on Earth 4.4 billion years ago would have supported liquid water, and possibly life.
"One of the things that we're really interested in is: When did the Earth first become habitable for life? When did it cool off enough that life might have emerged?" Valley told CBS News. "We have no evidence that life existed then. We have no evidence that it didn't. But there is no reason why life could not have existed on Earth 4.3 billion years ago."
The oldest known fossils are said to be 3.5 billion years old.
Photos by John Valley; Graphic by Andree Valley