for National Geographic News
Earth's early atmosphere may have been highly corrosive to rocks, gradually dissolving away all but the toughest of minerals, a new study suggests.
The findings could explain a gap in Earth's geologic record that has puzzled scientists.
"It's possible that [the new study] answers the riddle," said Takayuki Ushikubo, a geologist at the University of Wisconsin, who led the study published online in the journal Earth and Planetary Science Letters.
When Earth formed about 4.5 billion years ago, it was a fiery, inhospitable mass of rocks and gases.
(Related: Prehistoric Time Line)
Scientists believed this eraknown as the Hadean, or "hellish," era, for its molten seas of magmalasted until the planet was as much as 500 million years old.
However the new findings and other recent evidence bolsters the idea that Earth actually cooled quite quickly and became more like the planet we're used to within just a couple of hundred million years.
Over the last three to four billion years, Earth's tectonic plates have continually shifted around, and their minerals have been melted down and recyclederasing much of the early geologic history of our planet.
But tiny shards of very early rock have survived in the Jack Hills of western Australia. Some of these microscopic crystals, known as zircons, date to as much as 4.4 billion years ago.
"The Jack Hills zircons are the oldest objects from Earth and the only geochemical evidence we have of the earliest Earth history," Ushikubo said.
Ushikubo and his colleagues performed chemical analysis on the zircons to measure trace amounts of lithium.
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