Thursday, December 08, 2005

Early Earth likely had continents

The conventional view has been that continents and other conditions similar to what we have today did not develop until the planet was 500 million years old, about 4 billion years ago. Since there is some evidence of the existence of life when Earth was 600 to 700 million years old, life would have had to arise very quickly. But now it appears that the first continents may have appeared much earlier:

Early Earth Likely Had Continents And Was Habitable, Says New Study
A surprising new study by an international team of researchers has concluded Earth's continents most likely were in place soon after the planet was formed, overturning a long-held theory that the early planet was either moon-like or dominated by oceans.

The team came to the conclusion following an analysis of a rare metal element known as hafnium in ancient minerals from the Jack Hills in Western Australia, thought to be among the oldest rocks on Earth. Hafnium is found in association with zircon crystals in the Jack Hills rocks, which date to almost 4.4 billion years ago.


More details from another press release:

There was no such thing as hell on Earth
The research, published in the latest edition of Science, follows on from results by Professor Harrison and his colleagues published earlier this year that confirmed that our planet was also likely to have had oceans during most of the Hadean.

“A new picture of early Earth is emerging,” Professor Harrison said. “We have evidence that the Earth’s early surface supported water – the key ingredient in making our planet habitable. We have evidence that this water interacted with continent-forming magmas throughout the Hadean.

“And now we have evidence that massive amounts of continental crust were produced almost immediately upon Earth formation. The Hadean Earth may have looked much like it does today rather than our imagined view of a desiccated world devoid of continents.”

The dating was accomplished by measuring percentages of different isotopes of hafnium in the zircons.
[H]afnium isotope variations produced by the radioactive decay of an isotope of lutetium indicate many of these ancient zircons formed in a continental setting within about 100 million years of Earth formation.

“The evidence points to almost immediate development of continent followed by its rapid recycling back into the mantle via a process akin to modern plate tectonics,” according to Professor Harrison.

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