A recent analysis of the fossils of ancient microorganisms from deep within Earth’s past have unveiled the presence of a surprising amount of biodiversity that flourished roughly 3.4 billion years ago, when the Earth was still a very young planet. The variety of metabolic processes that these early microorganisms used suggests that they needed time to evolve the diversity that the researchers discovered, meaning that life on Earth had to have started much, much earlier. And if life on Earth took hold that quickly in its history, what would prevent the multitude of other planets we’re discovering across the universe from forming their own lifeforms?

Researchers from UCLA and the University of Wisconsin–Madison used samples of some of the world’s oldest-known fossils–3.465 billion years old, in fact–gathered from Western Australia. They then examined the ancient microorganisms using a technique called secondary ion mass spectroscopy (SIMS), to determine the ratio of specific isotopes found within the samples, in this case carbon-12 and carbon-13, to find out what the original organisms’ metabolic processes were. Organisms with different metabolisms will produce different C-12/C-13 ratios, allowing the researchers to differentiate between microbes that, for example, used photosynthesis, or used methane for fuel. "The differences in carbon isotope ratios correlate with their shapes," explains geoscience professor and head of the Wisconsin team, John Valley. "Their C-13-to-C-12 ratios are characteristic of biology and metabolic function."

This analysis revealed a relatively complex ecosystem made up of single-celled organisms with a variety of metabolisms, including two that employed a primitive form of photosynthesis, two more that consumed methane, and one that produced methane. This variety of metabolisms suggests that the origin of these microbes’ ancestors occurred much earlier in Earth’s history: bear in mind that these fossils were formed only about a billion years after the Earth itself came into being, meaning that life itself came about very early in the planet’s history.

"By 3.465 billion years ago, life was already diverse on Earth; that’s clear — primitive photosynthesizers, methane producers, methane users," said UCLA paleobiology professor and study lead J. William Schopf. "These are the first data that show the very diverse organisms at that time in Earth’s history, and our previous research has shown that there were sulfur users 3.4 billion years ago as well.

"This tells us life had to have begun substantially earlier and it confirms that it was not difficult for primitive life to form and to evolve into more advanced microorganisms."

The researchers have gone one step further, and are suggesting that if life began so early in Earth’s history, then it seems highly unlikely that it wouldn’t manifest on other worlds as well: statistically speaking, the odds of life on Earth being an accident unique in the cosmos is staggeringly low.

According to Schopf, "if the conditions are right, it looks like life in the universe should be widespread." Schopf plans on using the SIMS technique on rocks from Mars, brought back to Earth by a returning space probe, sometime in the future.

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