Geological evidence suggests that Earth may have had surface water -- and thus conditions to support life -- millions of years earlier than previously thought. Scientists reconstructed the portrait of early Earth by reading the telltale chemical composition of the oldest known terrestrial rock. The 4.4-billion year-old mineral sample suggests that early Earth was not a roiling ocean of magma, but instead was cool enough for water, continents, and conditions that could have supported life. The age of the sample may also undermine accepted current views on how and when the moon was formed. The research was supported in part by the National Science Foundation (NSF), and is published in this week's issue of the journal Nature.

"This appears to be evidence of the earliest existence of liquid water on our planet," says Margaret Leinen, assistant director of NSF for geosciences. "If water occurred this early in the evolution of earth, it is possible that primitive life, too, occurred at this time."

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, Colgate University, Curtin University in Australia and the University of Edinburgh in Scotland have found evidence that 4.4 billion years ago, 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 Valley, a geologist at UW-Madison. "At that time, the Earth's surface should have been a magma ocean. 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 o
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Contact: Cheryl Dybas
cdybas@nsf.gov
703-292-8070
National Science Foundation
8-Jan-2001