LIFE ON EARTH BEGAN AT LEAST 3.85 BILLION YEARS AGO

Wed, 6 Nov 1996 16:50:29 -0500
Source: NASA HQ Public Affairs Office

Donald Savage
NASA Headquarters, Washington, DC November 6, 1996
(Phone: 202/358-1547)

Stuart Wolpert
UCLA, Department of Earth and Space Sciences
(Phone: 310/206-0511

Cindy Clark
Scripps Oceanographic Institute, San Diego, CA
(Phone: 619/534-1294)

Cheryl Dybas
National Science Foundation, Arlington, VA
(Phone: 703/306-1070)

RELEASE: 96-230

LIFE ON EARTH BEGAN AT LEAST 3.85 BILLION YEARS AGO, 400 MILLION YEARS EARLIER THAN PREVIOUSLY THOUGHT, SCIENTISTS SAY

Life on Earth began at least 3.85 billion years ago, an international team of scientists reports in the cover story of the Nov. 7 issue of the journal Nature.

The scientists, from UC San Diego's Scripps Institution of Oceanography, UCLA's Department of Earth and Space Sciences, the Australian National University and England's Oxford Brookes University, present evidence that pushes back the emergence of life on Earth by 400 million years.

The evidence comes from a rock formation discovered on Akilia Island in southern West Greenland that is at least 3.85 billion years old. The research -- funded primarily by the National Science Foundation and NASA -- has provocative implications.

"Our evidence establishes beyond reasonable doubt that life emerged on Earth at least 3.85 billion years ago, and this is not the end of the story," said Stephen J. Mojzsis, a graduate student in geochemistry at Scripps and the lead author of the article. "We may well find that life existed even earlier."

"We look in rocks like this for chemical suggestions and isotopic evidence, and we found both," said T. Mark Harrison, professor of geochemistry at UCLA and director of UCLA's W.M. Keck Foundation Center for Isotope Geochemistry. "It would be wonderful to see a head and toes, and while we don't have those, we have found very strong isotopic evidence for ancient life."

"But in the cases of Earth's most ancient rocks and minerals, we are actually better off relying on this type of isotopic evidence -- chemofossils -- rather than on the shape of life-like objects with which nature has often been deceiving the unwary," said Gustaf Arrhenius, professor of oceanography at UC San Diego and principal investigator for the research project.

The carbon inclusions in the rock were analyzed with UCLA's high-resolution ion microprobe -- an instrument that enables scientists to learn the exact composition of samples -- which Mojzsis described as the "world's best instrument" for this research. The microprobe shoots a beam of ions -- charged atoms -- at a sample, releasing from the sample its own ions that are analyzed in a mass spectrometer. Scientists can aim the beam of ions at specific microscopic areas of a sample and analyze them.

The team of scientists, Mojzsis; Arrhenius, who is his research adviser; Harrison; Kevin McKeegan, a researcher in UCLA's Department of Earth and Space Sciences; Allen Nutman, a research fellow at the Australian National University; and Clark Friend, a geologist at Oxford Brookes University, presents the following evidence for the ancient life:

· Most importantly, a high ratio of one form -- an isotope -- of carbon to another, which provides a "signature of life," Mojzsis said. The carbon aggregates in the rock have a ratio of about 100 to one of 12C (the most common isotope form of carbon, containing six protons and six neutrons) to 13C (a rarer isotopic form of carbon, containing six protons and seven neutrons). "The light carbon, 12C, is more than three percent more abundant than scientists would expect to find if life were not present, and three percent is, in this case, a very large amount," Arrhenius said;

· The inclusion of the carbon in a phosphate mineral called apatite, which is also the material of which bones and teeth are made. Apatite is often formed by microorganics, but it can also be formed inorganically. The association of the carbon with the apatite is "suggestive, and not surprising, but does not in itself establish life," Arrhenius said.

The form of life discovered was probably a simple micro-organism, although its actual shape or nature cannot be ascertained, Mojzsis said, because heat and pressure over time have destroyed any original physical structure of the organisms.

Harrison, who directs UCLA's ion microprobe, said of the research, "This was a scientific problem that was waiting for a new generation microprobe of this resolution. The individual samples are very small, and no other instrument would have been sensitive enough to reveal precisely the isotopic composition and location of the carbon inclusions in the rock."

It is unknown when life first appeared on Earth, which is approximately 4.5 billion years old. The previous earliest evidence for life was presented by UCLA paleobiologist J. William Schopf, who showed that on the basis of bacteria-like fossils, primitive life, much like modern "pond scum," existed on Earth 3.46 billion years ago. "The evolution of lifeless matter into primitive life forms, and their organization into the complex structure of cells like those found by Schopf, represent an enormous development in the earliest history before the deposition of the Akilia sediments," Arrhenius said.

The residues of ancient life that the scientists have discovered existed prior to the end of the "late heavy bombardment" of the Moon by large objects, which ended approximately 3.8 billion years ago, Harrison said. The implication, he added, is that the often assumed simultaneous bombardment of Earth did not lead to the extinction of life.

This research shows that life on Earth began during the first approximately 700 million years after the formation of the planet, placing an upper limit on the time needed for the creation of life on Earth, or on the time period available for it to arrive here from elsewhere, the scientists said.

"Life is tenacious, and it completely permeates the surface layer of the planet," Mojzsis said. "We find life beneath the deepest ocean, on the highest mountain, in the driest desert and the coldest glacier, and deep down in the crustal rocks and sediments. Not knowing what conditions are needed for the emergence of life, it is only possible to speculate about its existence elsewhere in the universe. An important contribution to the solution of this problem could come from exploration of the surface of Mars for traces there of extinct life."

An equally interesting question, the scientists agreed, that is currently studied in laboratories on Earth is how life originally could have arisen from lifeless molecules, and evolved into the already sophisticated isotope fractioning life forms recorded in the Akilia rocks.

Mojzsis' research is supported by a graduate fellowship from the NASA Specialized Center for Organized Research and Training (NSCORT) in Exobiology, which is located at Scripps Institution of Oceanography. Arrhenius has received support from NASA's Exobiology Office, from NASA NSCORT and from the NSF (Earth Sciences). Harrison's ion microprobe research is supported by a grant from the NSF's Instrument and Facilities Program. Nutman's research has been supported by the Carlsberg Foundation and the Danish Natural Science Research Council. Friend's research has been supported by the Oxford Brookes University and the Royal Society of London.

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