Ancient Mummified Bacteria Point to Subterranean Origins of Life

October 22, 2015 | Sarah Tse

Underwater flange vents heated hydrogen and methane-rich fluids
Photo credit: NOAA Photo Library/Flickr (CC BY 2.0)

The discovery of fossilized bacteria in rock samples from deep beneath the ocean floor indicate that the very first life-forms arose from a rich soup of minerals concocted in hydrothermal vents.

The fathoms of the deep sea hold many mysteries that we have yet to explore. The latest discovery supports one of the leading theories about how life on Earth arose from inorganic substances through a process known as “abiogenesis.” Researchers from Woods Hole Oceanographic Institution (WHOI), Virginia Tech, and the University of Bremen have uncovered mummified evidence of ancient life in rocks from the Earth’s mantle below the seafloor.

The mantle is the layer of Earth that usually lies right beneath the crust, but tectonic forces during the Early Cretaceous Period drove pieces of the mantle up to the surface of the seafloor as the supercontinent Pangaea broke up into the land-masses we recognize today. As these mantle rocks made first contact with seawater, a series of chemical reactions turned the seawater into hydrothermal fluid full of hydrogen and methane. The seawater contributed dissolved carbon and “electron acceptors” (chemicals used by all living things to generate energy).

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This mixture is thought to have created a perfect storm of ingredients necessary to support life. And indeed, analysis of rock samples drilled from 700 m beneath the seafloor near the coast of Portugal revealed the presence of ancient colonies of bacteria and archaea, a type of single-celled microorganism even more ancient than bacteria. These microbes flourished in this soup of life-sustaining ingredients, but they met their doom as they were entombed in the very minerals that fed them.

As a result, their cellular structures were almost perfectly preserved when, over 100 million years later, the researchers tested the samples for the presence of organic molecules like amino acids, proteins, and “lipids” (fats). Furthermore, the lipids from these samples matched those recovered from a modern day hydrothermal system that is believed to mirror ancient sites where life may have first emerged.

Although these particular microbial remains are much younger than the most ancient traces of life, which are dated to 3.5 billion years ago, they hint at the developments that may be responsible for those first stirrings. This vital mixture of chemicals arose independently, simply from the geological processes occurring beneath the surface. These conditions were likely replicated at multiple points throughout Earth’s history.

This finding is even more intriguing because this pattern of events could happen on any other rocky planet that contains water, like certain moons of Jupiter and Saturn. As long as a planet is geologically active, and contains enough water to interact with those active rocks, another primordial soup could easily form and commence the evolution of life. The exact processes by which unicellular organisms assembled from these primary organic building blocks has yet to be determined. Further research into the exact nature of these ancient microbes, as well as sampling similar sites, will reveal more about the mysterious beginnings of life on Earth.

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