Ancient mineral shows early Earth climate tough on continents

Ancient mineral shows early Earth climate tough on continents
Pictured is a false-color microscope image of a 4-billion-year-old zircon, a tiny mineral used to study the ancient rocks in which it formed. Chemical analysis of this crystal by UW-Madison geologists Takayuki Ushikubo and John Valley suggests that rocky continents and liquid water existed on Earth at least 4.3 billion years ago. Evidence of heavy weathering by a harsh climate may help explain why no rock samples older than 4 billion years have ever been found. Photo courtesy Mary Diman and John Valley



Valley previously used these tiny mineral grains — smaller than a speck of sand — to show that rocky continents and liquid water formed on the Earth much earlier than previously thought, about 4.2 billion years ago.




Previous explanations for the missing rocks have included destruction by barrages of meteorites and the possibility that the early Earth was a red-hot sea of magma in which rocks could not form.


"At 4.3 billion years ago, the Earth already had habitable conditions," Ushikubo says.




Carbon dioxide in the atmosphere can combine with water to form carbonic acid, which falls as acid rain. The early Earth's atmosphere is believed to have contained extremely high levels of carbon dioxide — maybe 10,000 times as much as today.

"At [those levels], you would have had vicious acid rain and intense greenhouse [effects]. That is a condition that will dissolve rocks," Valley says. "If granites were on the surface of the Earth, they would have been destroyed almost immediately — geologically speaking — and the only remnants that we could recognize as ancient would be these zircons."

Source: UW-Madison

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Citation: Ancient mineral shows early Earth climate tough on continents (2008, June 13) retrieved 23 June 2021 from https://phys.org/news/2008-06-ancient-mineral-early-earth-climate.html

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