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Investigating hydrothermal vents, geochemist Frieder Klein from Woods Hole Oceanographic Institution in the US has discovered a variation on the deep-sea origin story. He has found evidence of life in rock below the sea floor which might have provided the right environment for life to start.

Klein and colleagues were looking at samples from cores drilled from the Iberian continental margin off the coast of Spain and Portugal in 1993. The samples came from rock 760m below the current sea floor, which would have been 65m below the early unsedimented ocean floor. He saw some unusual looking veins in the samples, composed of minerals also found at the Lost City hydrothermal system. ‘That was intriguing to me because this mineral assemblage is only formed when you mix hydrothermal fluids with seawater,’ says Klein. This suggests similar chemistry could be going on below the sea floor.

Within these veins, dated to 120 million years ago, Klein’s team found inclusion of fossilized microbes. He suggests the desiccating properties of the mineral brucite (Mg (OH)2) might explain the preservation of organic molecules from the microbes. These included amino acids, proteins and lipids which were identified by confocal Raman spectroscopy. Klein says he was initially skeptical, but analysis of extracted samples confirmed unique lipid biomarkers for sulfate-reducing bacteria and archaea, which are also found in the Lost City hydrothermal vents system.5 SEM imaging showed carbon inclusions which he says ‘seemed to look like micro-colonies of micro-organisms’

While obviously these samples are much younger, ‘The presence of these microbes is telling us that life is possible in sea floor environments in hydrothermal systems, that were probably present and active throughout most of the early earth,’ Klein observes. ‘The sub-sea floor represents another more protected environment.’