Oldest fossils hold clue to origin of life

Life on Earth may have originated earlier than thought and could have done so in hydrothermal vents on the ocean floor. A new study in Nature finds the origin of life at at least 3,770 million and possibly 4,290 million years ago in ferruginous sedimentary rocks, interpreted as seafloor-hydrothermal vent-related precipitates from the Nuvvuagittuq supracrustal belt of Eastern Canada. Scientists led by Dr. Dominic Papineau of University College London made the discovery.

Epifluorescence imaging of modern vent samples has shown that cylindrical casts composed of iron oxyhydroxide are formed by bacterial cells and are undeniably of biological origin (biogenic). Hence, morphologically similar tubes and filaments in ancient jaspers may be taken as evidence that the jaspers held organisms that can survive elevated temperatures.

“The fact that we found microfossils in these rocks shows that within only a few hundred million years of the accretion of the Earth, life had not only originated, but had also already diversified into specialised microorganisms living in hydrothermal vent environments where biologists have been suggesting for years that that was the site for the origin of life on Earth,” noted Dr. Papineau in an email to this Correspondent.

The scientists found that NSB rocks contain graphite with ratios of the 13C/12C isotopes (the two naturally occurring stable isotopes of carbon – 13C having one more neutron than 12C) indicative of biological metabolism. The mineral graphite is composed of carbon and can form during the metamorphism of biological organic matter. It is the same for carbonate, but these minerals represent oxidised organic matter.

Rosette remnants

Microscopic spheroidally-concentric mineral structures called rosettes were found in the NSB rocks and are composed of apatite (the phosphate mineral in our teeth and bones), carbonate, and graphite. Also found were granules which are similar to rosettes, but slightly larger, up to 2 mm in diameter. The granules contain different iron minerals that indicate the former presence of chemical reactions. The scientists believe that both rosettes and granules are the mineralised products of putrefaction.

On the basis of chemical and morphological lines of evidence, the tubes, filaments and granules are best explained as remains of iron-metabolising (consuming iron) filamentous bacteria, and therefore represent the oldest life forms recognized on Earth.

“Some bacteria can literally eat iron, which is what we think these ones were doing more than 3.77 billion years ago. All these lines of evidence have also been documented in younger jasper that formed when we know life existed, as well as in modern ferruginous-siliceous (iron–silica containing) precipitates in the vicinity of hydrothermal vents. Hence, we conclude that we have found the oldest fossils known,” Dr. Papineau says.

Recommended for you