When scientists claimed more than a decade ago that tiny crystals in Australia were 4.4 billion years old, they faced skepticism. The Earth itself, after all, is 4.5 billion years old, the Sydney Morning Herald notes. "Nothing in science goes without being questioned," geochemist John Valley tells NPR. Now, however, his team has proven the crystals' age is correct—in other words, they're the oldest Earth-formed materials ever found. Researchers dated the crystals, which need magnification to be seen, by investigating how much of the uranium within them had turned into lead. But that standard dating method wasn't enough to convince some fellow scientists.
Doubters pointed out that as time went by, lead atoms could have shifted around inside the crystal, potentially resulting in inaccurate readings. So the experts turned to a process called atom-probe tomography, which allowed them to map out specific atoms, NPR reports. The study showed that, in fact, the atoms hadn't moved much. Now, "we've proved that the chemical record inside these zircons is trustworthy," Valley tells LiveScience. The findings indicate that the Earth may have been able to host life earlier than had been believed: "there is no reason why life could not have existed on Earth 4.3 billion years ago," Valley says.