Astro Update: How Old Is Life On Earth?

Layer-deflecting lens of red iron-silica rock bounded by veins of white calcite, which have sourced some of their carbon from the decayed primitive microbes. Nuvvuagittuq Supracrustal Belt, Québec, Canada. Photo by D. Papineau

How old is life on Earth, and how do we know?

The answer of course, is fossils. But what kind of fossil records do early life-forms – single-celled organisms with no shells or bones – leave behind? The answer may be: rust.

Researchers from NASA and the University of London announced that they discovered what may be the world’s oldest fossil to date: rust-colored tube-like structures similar to those created by single-celled organisms living near today’s deep-ocean vents. These newly-discovered ancient fossilized tubes are tiny – half the width of a human hair – and are hence called microfossils. The microfossils’ rusty color comes from the iron that these microscopic creatures used as an energy source when they lived near the ocean floor at least 3.77-billion years ago.

In their paper published in Nature, Dr. Dodd and his colleagues described how they used lasers to slice rocks from North Quebec into thin sections that finally revealed the organisms’ bent, reddish tubular structures. If their findings are correct, the age of the oldest life on earth is hundreds of millions of years older than the previously believed, and possibly much more ancient than that.

Haematite filament attached to a clump of iron in the lower right, from hydrothermal vent deposits in the Nuvvuagittuq Supracrustal Belt in Québec, Canada. These clumps of iron and filaments were microbial cells and are similar to modern microbes found in vent environments. Photo by M. Dodd

The life-forms that created these structures may have been born in a time not too long after, on the cosmic scale, the Earth itself formed. Prior to this discovery, the oldest record of life came from stromatolites – fossilized microbial mats – found on a rocky outcropping in Greenland, projected to be at most 3.7-billion years old.

From the perspective of astrobiology, this new finding is good evidence for how early life can emerge given the right environment. Currently, we believe that similar environments to the one where these fossils formed might be found deep under the oceans of Europa and Enceladus – and on many other bodies in our Solar System.