Sea-floor hydrothermal vent sites as modern equivalents of the earliest ecosystems on Earth is an intriguing hypothesis, but one that has no supporting evidence from the geologic record. We have therefore analyzed the organic content of samples representative of sea-floor hydrothermal activity from ∼ 3.2 Ga, as well as samples up to the present, including active sea-floor hydrothermal deposits. The mass spectroscopy results show that a great variety of organic compounds is present in all the samples. The data are essentially indistinguishable between the various samples, irrespective of their age. These findings imply, among other things, that organic productivity associated with sea-floor hydrothermal environments was already vigorous as early as the Middle Archean, supporting the premise that life may have started near vent sites. However, abundant organic material in concomitant pelagic sediment (shale), together with supporting carbon isotopic evidence, shows that a photosynthetic marine biota was probably also active at this time. Thus, ecosystems related to sea-floor hydrothermal activity and photosynthetic microorganisms in the ambient ocean coexisted at 3.2 Ga, indicating that these earliest ecosystems must have been in existence well before this time.

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