New evidence for the presence of liquid water at or near the Earth's surface 4.3 billion years ago has been discovered by a team of scientists, hinting that the environments for life may have emerged on Earth much earlier than previously thought.
According to University of Colorado at Boulder Assistant Professor Steven Mojzsis, lead author of the study, the new research pushes back evidence for water on or near Earth聮s surface by roughly 400 million years.
"The stage appears to have been set 4.3 billion years ago for life to emerge on Earth," said Mojzsis, who recently took a faculty position in the CU-Boulder geological sciences department after postdoctoral work at the University of California, Los Angeles. "There probably was already in place an Earth with an atmosphere, an ocean and a stable crust within about 200 million years of the Earth's formation."
Earth is believed by scientists to have formed about 4.5 billion years ago.
A paper on the subject by Mojzsis, UCLA geochemistry Professor T. Mark Harrison and geology Professor Robert Pidgeon at Curtin University of Technology in Perth, Australia, appears in the Jan. 11 issue of the journal Nature.
"Many geochemists believe that maintaining stable liquid water on a planetary surface that early is the most difficult of three conditions needed for life to emerge: energy, organic materials and liquid water," Mojzsis said.
"The conditions for life were established very early on Earth, and this suggests that such conditions might not be uncommon in the universe. If it happened so early on, why couldn't it happen elsewhere in the universe as well? Life may not be so difficult to form when these three conditions are met."
The scientists analyzed sediment from Western Australia that was more than 3 billion years old with UCLA's high-resolution ion microprobe 聳 an instrument that enables scientists to date and learn the composition of rock samples. The microprobe shoots a beam of charged atoms, or ions, at a rock sample, releasing ions from the sample that can then be analyzed.
The scientists found that while the rock was deposited about 3 billion years ago, it contains ancient mineral grains known as zircons that are much older. Two of the zircon grains were 4.3 billion years old, and nearly a dozen others were older than 4 billion years.
Zircons are heavy, durable minerals related to the synthetic cubic zirconium used for imitation diamonds and costume jewelry. The zircons studied in the rock are about twice the thickness of a human hair.
By studying the ratio of oxygen isotopes in the zircon samples, the research team discovered a distinctive oxygen isotopic signature that significantly predates Earth's oxygen atmosphere, said Harrison. The isotopic signature indicates zircon interacted with cold water on Earth聮s surface about 4.3 million years ago.
"These zircons tell us that they melted from an earlier rock that had been on the Earth's surface and interacted with cold water," Harrison said. "There is no other known way to account for that heavy oxygen."
"The microprobe is a fantastic instrument in its sensitivity, its accuracy and its versatility," said Mojzsis, also a member of CU-Boulder聮s NASA-sponsored Astrobiology Institute. "With the microprobe, we can determine the oxygen isotopic composition of individual spots within the tiny zircons, and measure with enormous precision the ages of these spots. We can determine when the zircons formed and how they formed."
The research was funded by the National Science Foundation and NASA's Center for Astrobiology. Harrison can be contacted through Stuart Wolpert in the UCLA Media Relations Office at (310) 206-0511. Digital photos of the ancient rock are available by contacting Mojzsis either by phone or e-mail.