Found more than a decade ago on a sheep farm in Australia was a small crystal, which scientists now say could be the oldest piece of Earth’s history.
The study from the University of Wisconsin-Madison says that the zircon found in a rock outcrop in the Jack Hills region of western Australia is the “oldest known material of any kind formed,” dated at 4.4 billion years old.
John Valley, a geochemist, said the crystal, which is only as thick as about two strands of human hair, Reuters noted, sheds light on the details of Earth’s crust formation.
“This confirms our view of how the Earth cooled and became habitable,” Valley said, according to the university’s website. “This may also help us understand how other habitable planets would form.”
According to the study’s abstract, published in the journal Nature Geoscience, zircons are the only materials that could represent the early history of Earth’s formation.
Some scientists had posited that dating techniques of zircon crystals could give a false age, but the researchers in this study used a second technique that found “age biasing impossible,” as the study abstract put it.
The University of Wisconsin described more on this technique:
The study was conducted using a new technique called atom-probe tomography that, in conjunction with secondary ion mass spectrometry, permitted the scientists to accurately establish the age and thermal history of the zircon by determining the mass of individual atoms of lead in the sample. Instead of being randomly distributed in the sample, as predicted, lead atoms in the zircon were clumped together, like “raisins in a pudding,” notes Valley.
The clusters of lead atoms formed 1 billion years after crystallization of the zircon, by which time the radioactive decay of uranium had formed the lead atoms that then diffused into clusters during reheating. “The zircon formed 4.4 billion years ago, and at 3.4 billion years, all the lead that existed at that time was concentrated in these hotspots,” Valley says. “This allows us to read a new page of the thermal history recorded by these tiny zircon time capsules.”
Given the age of the crystal, scientists believe that Earth’s cooling occurred relatively soon after its being in a molten state, which they say was about 4.5 billion years ago.
Reconstructing Earth’s early history in this way could give scientists clues as to when life could have started.
“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 said, according toReuters.
Watch this report on the study’s findings from the Sydney Morning Herald:
Though the oldest bacterial evidence in the fossil record is dated at 3.4 billion years old, Valley told Reuters that with these recent findings, “there is no reason why life could not have existed on Earth 4.3 billion years ago.”