A paper in Nature last week blew my mind from several different perspectives.
Entitled, "Evidence for Early Life in Earth's Oldest Hydrothermal Vent Precipitates," it sounds at first like something that could only possibly interest paleontology and/or geology geeks. But as soon as you start looking closely, you find that what this paper describes is groundbreaking.
The group, led by Matthew Dodd of University College London, thin-sliced rock excavated from a piece of the Nuvvuagittuq Supracrustal Belt in Québec, one of the oldest intact rock formations on Earth. And I do mean thin; the rock slices were, on average, 100 microns thick, or about the thickness of a sheet of printer paper. And "old" is no exaggeration, either. The rock is estimated at four billion years old, only three hundred million or so years after the crust solidified from molten magma.
The rock is an iron-rich sedimentary rock that formed at a hydrothermal vent -- a fissure on the deep ocean floor that is spitting out geothermally-heated, mineral-rich water. We still have these around, mostly in places where the tectonic plates are moving apart, like the Mid-Atlantic Ridge, and even today they host a biome that is unlike any other on Earth. There are species of shrimp, tube worm, sponges, and bacteria found nowhere else. Not only that, they are one of only a handful of communities that is disconnected, energetically, from the Sun. Everything else -- so, almost all life on Earth -- can trace the energy that makes it go back down the food chain and ultimately to a photosynthesizer (usually plants or phytoplankton), which are powered by sunlight. The hydrothermal vent organisms, on the other hand, are powered by chemical reactions between the seawater and the hot stone of the upper mantle.
And when the scientists looked at the thin slices of the four-billion-year-old rock from Québec, they found...
The fossil traces are almost certainly from thermophilic bacteria, but form a colonial structure nearly a centimeter long. It includes tubes, branching filaments, and spheres that are (the researchers claim) too complex to be explainable by inorganic chemical reactions. This pushes the earliest life forms back by almost a third of a billion years earlier than the previous estimate, so we're not talking about a small shift, here."Using many different lines of evidence, our study strongly suggests a number of different types of bacteria existed on Earth between 3.75 and 4.28 billion years ago," said study co-author Dominic Papineau, in an interview with GeologyIn. "This means life could have begun as little as 300 million years after Earth formed. In geological terms, this is quick – about one spin of the Sun around the galaxy."