#91: Unmasking Earth’s First Life

Paleontologists discover what may be the oldest fossilized bacteria ever found, but questions remain.

By Mary Beth GriggsDec 22, 2011 6:00 AM


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In August Oxford University paleontologist Martin Brasier announced that he had found the remains of one of the earliest life-forms on Earth, fossilized 3.4-billion-year-old bacteria. The claim brought additional intrigue to the ongoing contention between Brasier and UCLA’s Bill Schopf, who in 1993 said he had discovered organisms 3.46 billion years old. Brasier publicly questioned Schopf’s find in 2002, and the two have been feuding ever since.

The quarrel is juicy enough in itself, but it also carries major scientific importance: The discoveries provide contrasting insights into the identity of Earth’s first organisms, as well as what life might look like beyond our planet.

Earth was very different 3.4 billion years ago. No plants grew on the few areas of land that poked above a hot, shallow, Earth-enveloping sea. Meteors struck frequently; the atmosphere was full of sulfur and carbon dioxide and short on oxygen. Yet scientists believe these were the conditions that gave rise to life.

According to Schopf, the fossils he found in Western Australia indicate that Earth’s earliest inhabitants resembled cyanobacteria, single-celled organisms that turn sunlight into energy. Analysis of the surrounding rock suggests they lived in a sea near hydrothermal vents pumping out hot, mineral-laden water.

Brasier’s find was just 20 miles away from Schopf’s, but it comes with a vastly different interpretation. Mineral evidence near his fossils indicates that these creatures fueled themselves primarily with sulfur instead of light, Brasier says, and lived in shallow waters near the shore.

Paleontologists will keep reviewing evidence to determine which interpretation is more accurate. For now, both discoveries are providing scientists with models for the types of life-forms that could exist on other planets. “When I was young, everyone lost interest if it wasn’t little green men,” Brasier says. “But now we want to know if there is other life out there, even on the bacterial level.”

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