Study: Simple Life Forms are Common Throughout Universe
A detailed analysis of 3.465-billion-year-old microbial microfossils provides evidence to support an increasingly widespread understanding that life in the Universe is common.
Professor J. William Schopf from the University of California, Los Angeles, and his colleagues analyzed 11 specimens of 5 species of prokaryotic cellular microfossils from the Apex Basalt Formation, Pilbara Craton, Western Australia.
Two of the five species the researchers studied were primitive photosynthesizers, one was an Archaeal methane producer, and two others were methane consumers.
“The evidence that a diverse group of organisms had already evolved extremely early in the Earth’s history strengthens the case for life existing elsewhere in the Universe because it would be extremely unlikely that life formed quickly on Earth but did not arise anywhere else,” they said.
The study, published in the Proceedings of the National Academy of Sciences, is the most detailed ever conducted on microorganisms preserved in such ancient fossils.
“By 3.465 billion years ago, life was already diverse on Earth; that’s clear — primitive photosynthesizers, methane producers, methane users,” Professor Schopf said.
“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.”
“Scientists still do not know how much earlier life might have begun. But, if the conditions are right, it looks like life in the Universe should be widespread.”
Professor Schopf and co-authors analyzed the Apex specimens with cutting-edge technology called secondary ion mass spectroscopy (SIMS), which reveals the ratio of carbon-12 to carbon-13 isotopes — information scientists can use to determine how the microorganisms lived.
They used a secondary ion mass spectrometer — one of just a few in the world — to separate the carbon from each fossil into its constituent isotopes and determine their ratios.
“The differences in carbon isotope ratios correlate with their shapes. Their carbon-12 to carbon-13 ratios are characteristic of biology and metabolic function,” said co-author Professor John Valley, from the University of Wisconsin, Madison.
“The fossils were formed at a time when there was very little oxygen in the atmosphere,” Professor Schopf added.
“I think that advanced photosynthesis had not yet evolved, and that oxygen first appeared on Earth approximately half a billion years later before its concentration in our atmosphere increased rapidly starting about 2 billion years ago.”
“Oxygen would have been poisonous to these microorganisms, and would have killed them,” the scientist said.
Primitive photosynthesizers are fairly rare on Earth today because they exist only in places where there is light but no oxygen — normally there is abundant oxygen anywhere there is light.
And the existence of the rocks the team analyzed is also rather remarkable.
“The average lifetime of a rock exposed on the surface of the Earth is about 200 million years,” Professor Schopf noted.
“When I began my career, there was no fossil evidence of life dating back farther than 500 million years ago. The rocks we studied are about as far back as rocks go.”
“While the study strongly suggests the presence of primitive life forms throughout the Universe, the presence of more advanced life is very possible but less certain,” he said.
J. William Schopf et al. SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions. PNAS, published online December 18, 2017; doi: 10.1073/pnas.1718063115