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Stromatolites produce methane

Scientist from the Department of Geodynamics and Sedimentology find chemical signatures of methane producing stromatolites. The stromatolites occur in Lagoa Salgada, a highly saline lagoon in Brazil, and they may reproduce conditions as they prevailed 2.3-1.9 billion years ago, soon after Earth‘s atmosphere first became oxygenated.

Stromatolites are layered sedimentary structures that are considered the earliest trace of life on Earth. Two scientists from the University of Vienna, Daniel Birgel and Patrick Meister, are studying these living fossils together with their colleagues at ETH Zürich and the University of Campos dos Goytacaces (Brazil). In the May issue of the Journal Geobiology they report unusually high ratios of the two isotopes carbon-13 and carbon-12 in the stromatolites. As methane gas shows a very low ratio of these two isotopes, a high ratio in the carbonate suggests that over time the stromatolites released large amounts of this strong greenhouse gas to the atmosphere. Methane release is supported by fossil molecules derived from methane-producing microorganisms that became entombed in the calcified structure of the stromatolites. This system hence expands our spectrum of possible environments that may have existed on the early Earth.

Conceptual model for different factors under which different types of stromatolites grow. Methane producing stromatolites may be favoured if evaporation is high but sulphate input from seawater is low.



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