Life on Earth traced back 3.5 billion years

PERTH -- Deep in a remote, hot, dry patch of northwestern Australia lies one of the earliest detectable signs of life on the planet, tracing back nearly 3.5 billion years, scientists say.

At that time, the Earth -- relatively speaking -- wasn't into its adulthood yet. Scientists estimate the planet formed roughly 4.5 billion years ago; minerals known as zircons, indicating water, and continents existed within 100 million and 200 million years after that on what was still a scalding planet.

The existence of water suggests that life was possible. But what did it look like, and when did it start?

The discovery from the Dresser Formation, a much examined outcrop of rocks in Western Australia's Pilbara region, documented in a paper published online this week in the Astrobiologyjournal may help answer those questions.

It centers on something called microbially induced sedimentary structures, commonly shortened to the acronym MISS. It's a mouthful to many, but some scientists believe this phenomenon could be the key to finding the first demonstrable evidence of life.

A MISS forms via a process involving microorganisms (found in what's called microbial mats) with rocks (or sediment), something that can only happens under certain conditions.

As the study's lead author, Nora Noffke of Old Dominion University, notes, "The signal of early life forms has been preserved more clearly in MISS" compared with other prehistoric finds. Another unique thing about them, unlike some other geological phenomena, is that a MISS structure formed a few billion years ago can look much like one a few hundred-thousand years old. Yet another is that it can show not just evidence of one organism but an entire ecosystem, one in which living things coexisted with one another.

That's exactly what the study's co-authors -- Noffke, Daniel Christian, David Wacey and Robert Hazen -- say they found in Australia, noting that "this MISS displays the same associations that are known from modern as well as fossil" finds. The MISS also shows microbes that act like "modern cyanobacteria," which the co-authors explain are "known to be the first oxygen-producing organisms in the fossil record."

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