ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Thursday, November 7, 1996 TAG: 9611070072
SECTION: NATIONAL/INTERNATIONAL PAGE: A-4 EDITION: METRO
SOURCE: Los Angeles Times
Dramatically pushing back the emergence of life on Earth by nearly 400 million years, scientists Wednesday said they found chemical traces in the world's oldest known sediments that suggest simple life forms thrived 3.85 billion years ago.
The discovery could be the first evidence of the primordial microbes that arose when inanimate matter organized itself into the earliest living molecules.
The finding, published today in the journal Nature, raises a host of provocative possibilities about life at the dawn of time - a period when many experts believe the primitive Earth still was hot from the oven of creation. One scientist suggested it may be the trace of primitive organisms that had a radically different biochemistry from that which drives all modern living things, while others said it bolsters the idea that life did not originate on Earth at all.
In an unusual rock formation on Akilia Island in West Greenland, researchers from the Scripps Institution of Oceanography in San Diego and UCLA found what they believe is the distinctive signature of Earth's earliest life: traces of carbon isotopes and other organic evidence of primitive metabolisms, locked inside microscopic grains of a mineral called apatite.
The carbon isotopes were discovered in Greenland rocks that may have formed the floor of Earth's first ocean between 3.8 billion and 3.87 billion years ago. Earth itself is about 4.5 billion years old, and the oldest known physical fossils, which resemble modern bacteria, are about 3.46 billion years old.
Almost nothing is known for certain about Earth's earliest history or the conditions under which life arose. In the time since the Greenland rocks formed, their sediments have been so churned, broiled and squeezed in the mold of time - at pressures up to 5,000 atmospheres and temperatures in excess of 900 degrees Fahrenheit - that no direct physical fossil evidence of the early life forms survives. But if the scientists are correct, the traces left by their body chemistry have been preserved.
John M. Hayes, a leading authority at the Woods Hole, Mass., Oceanographic Institution in the chemistry of early Earth, called the research ``very notable.'' But he said it ``should also inspire caution.
``It is evidence for an isotope effect, not evidence of life,'' he said. ``It is great if it is true, but we have to know a lot more before we can take this to the bank. There are questions.'' And the largest of those questions, he said, may be the simplest: ``If this is true, what does it mean?''
Gustaf Arrhenius, a senior Scripps scientist involved in the project, said the chemical fossils could be remnants of the living sludge whose biochemistry preceded modern DNA-based life forms.
If true, the organisms were spawned in the so-called ``RNA World'' in which the chemical recipe used by living things to reproduce, change and evolve was carried out by single, primitive molecules, rather than today's more sophisticated chemical systems.
In this theoretical world, the DNA system that serves as the blueprint for all living things had yet to evolve. Instead, its molecular functions were handled entirely by a simpler RNA-based system. Today RNA serves only as a messenger in the more complex DNA system.
``It might be the first trace of the RNA world known to us,'' Arrhenius said.
While some experts found that idea far-fetched, others like Hayes said the discovery bolsters the idea that life did not originate on Earth at all. The fossils push the origin of life on Earth into a period when the planet is thought to have been under a lethal rain of meteors that could have obliterated any fledging native life easily.
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