Abstract :
[en] Defining biosignatures, i.e. features that are indicative of past or present life, has been one of the major strategies developed over
the last few years for the search of life on the early Earth and in the solar system. Current knowledge about microscopic remnants
of fossil organisms, namely microfossils are reviewed, focusing on: (i) studies of recent environments used as analogues for the
early Earth or extraterrestrial environments; (ii) examination of Precambrian rocks; and (iii) laboratory experiments simulating
biotic and abiotic processes and resulting in the formation of genuine or pseudomicrofossils. Fossils’ preservation depends on
environment and chemical composition of the primary structure, although they might undergo taphonomic processes that alter their
morphology and/or composition. Altogether, these examples illustrate what can be potentially preserved during the very first stages
of fossilization and what can be left in the geological record after diagenesis and metamorphism. Finally, this provides a rationale
to tentatively define diagnosis criteria for microfossils or ways to look for life on Earth or in extraterrestrial environments.
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