Washington, June 20 : By analyzing elements in ancient mineral crystals, scientists have suggested that 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.
According to a report in Discovery News, 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 so molten hot that 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," said Valley.
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, 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, thus pushing back the date for liquid water to 4.3 billion years ago.
The ratio of lithium isotopes in the crystals bore the signature of heavy weathering.
"Because we see it so commonly, it suggests that weathering was really extensive on the early Earth," said Valley.
People have thought for a long time that the early atmosphere might be carbon-dioxide-rich.
High CO2 levels - perhaps 10,000 times more - would have led to extreme acid rain, which would have dissolved the less-resistant minerals of the Earth's early crust, and could explain why rock from more than 4 billion years ago has so far been impossible to find.
If liquid water existed on Earth that long ago, the conditions could already have supported life.
"What our samples suggest is that the Earth was habitable. It was a relatively friendly environment," said Valley.