Earth May Have Supported Life Earlier in History

June 19, 2008 -- Analysis of elements in ancient mineral crystals suggests liquid water existed on Earth as long as 4.3 billion years ago, 100 million years earlier than previously thought, which may mean that Earth's conditions then could have supported life.

No rocks have been found on Earth older than 4 billion years, which led many geologists to believe that for the 550 million years of Earth's existence prior to that, the world was literally hellish -- so molten hot it prevented solid rock from forming.

But 25 years ago in a remote part of western Australia, researchers found a few grains of the mineral zircon -- a mineral that's extremely resistant to chemical changes -- that were older than 4 billion years old. In 2001, John Valley of the University of Wisconsin-Madison and colleagues reported finding a zircon that was 4.4 billion years old.

"People thought, 'Well, those have obviously come out of rocks that have been destroyed,'" Valley said.

Researchers hypothesized that perhaps there had been a large meteorite bombardment that destroyed the rocks the zircons came from.

But more recent evidence by Valley and colleagues has suggested a different explanation.

In subsequent experiments they analyzed oxygen isotopes in zircons that suggested that by 4.2 billion years ago, the Earth was no longer hellishly hot, but at a low enough temperature that liquid water would have been present.

In the latest findings, published online in Earth and Planetary Science Letters, Valley, along with Takayuki Ushikubo and other colleagues looked at a new ion, lithium.

The high amounts of lithium in the zircons suggested that the crystals formed at relatively cool temperatures -- pushing back the date for liquid water to 4.3 billion years ago.