Discovered in slices of rock recovered from northern Quebec, the microscopic metallic detritus—plus chemical signatures associated with ancient metabolisms—could push back the date at which life arose on Earth. If verified, these fossils would surpass 3.7-billion-year-old microbial mats found in Greenland as the oldest known traces of life.
Another study, suggests that eukaryotes (more complex life) — the domain of life comprising animals, plants, and protists — were present on Earth as early as 2.33 billion years ago, right around the time when oxygen became a permanent fixture in the atmosphere. This new time-stamp for ancient life significantly predates the earliest sign of eukaryotes found in the fossil record —1.56 billion-year-old macroscopic fossils that scientists widely agree are the remains of multicellular algae-like organisms.
The MIT researchers arrived at their estimate not by examining rocks for fossil evidence but by using a technique called “molecular clock analysis.” This approach involves first sifting through DNA databases to trace the evolution of particular gene sequences across hundreds of modern species. Then, using ages derived from the fossil animal and plant relatives, these sequences can be tied backward in time to the earliest point at which those sequences must have been expressed in ancestral eukaryotes.
Nature - Evidence of Very Early Life in Earth's oldest hydrothermal Vent precipitates
Although it is not known when or where life on Earth began, some of the earliest habitable environments may have been submarine-hydrothermal vents. Here we describe putative fossilized microorganisms that are at least 3,770 million and possibly 4,280 million years old in ferruginous sedimentary rocks, interpreted as seafloor-hydrothermal vent-related precipitates, from the Nuvvuagittuq belt in Quebec, Canada. These structures occur as micrometre-scale haematite tubes and filaments with morphologies and mineral assemblages similar to those of filamentous microorganisms from modern hydrothermal vent precipitates and analogous microfossils in younger rocks. The Nuvvuagittuq rocks contain isotopically light carbon in carbonate and carbonaceous material, which occurs as graphitic inclusions in diagenetic carbonate rosettes, apatite blades intergrown among carbonate rosettes and magnetite–haematite granules, and is associated with carbonate in direct contact with the putative microfossils. Collectively, these observations are consistent with an oxidized biomass and provide evidence for biological activity in submarine-hydrothermal environments more than 3,770 million years ago.