MADISON - Reading the telltale chemical signature of a mineral sample determined to be the world's oldest known terrestrial material, scientists have reconstructed a portrait that suggests the early Earth, instead of being a roiling ocean of magma, was cool enough to have water, continents and conditions that could have supported life.
Moreover, the age of the 4.4-billion-year-old sample may also undermine accepted views on the formation of the moon.
By probing a tiny grain of zircon, a mineral commonly used to determine the geological age of rocks, scientists from the University of Wisconsin-Madison, Curtin University in Australia and the University of Edinburgh in Scotland have found evidence that 4.4 billion years ago, a mere 100 million years or so after the accretion of the Earth, temperatures had cooled to the 100-degree Centigrade range, a discovery that suggests an early Earth far different from the one previously imagined.
"This is an astounding thing to find for 4.4 billion years ago," says John W. Valley, a UW-Madison professor of geology and geophysics. He is co-author of two papers, one in Nature (Jan. 11) and another in press at Geochimica et Cosmochimica Acta, an international science journal. Both articles paint a picture of a precocious young Earth complete with a low-temperature environment, oceans, thebeginnings of continents and conditions suitable for life. "At that time, the Earth's surface should have been a magma ocean," says Valley. "Conventional wisdom would not have predicted a low-temperature environment. These results may indicate that the Earth cooled faster than anyone thought."
Previously, the oldest evidence for liquid water on Earth, a precondition and catalyst for life, was from a rock estimated to be 3.8 billion years old.
The new picture of the earliest Earth is based on a single, tiny grain of zircon from western Australia found and dated by Simon A. Wilde, a professor in the School of Applied Geology at
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Contact: John Valley
valley@geology.wisc.edu
608-263-5659
University of Wisconsin-Madison
10-Jan-2001