Microbial palaeontology and the origin of life: a personal approach
Résumé
Palaeontology is an essential tool for tracing the history of life in the geological record. However, access to the origin oflife is blocked because of the lack of preservation of suitable rocks dating from the fi rst billion years of Earth’s history. Nevertheless, studyof Early Archaean rocks (~4-3.3 Ga) indicates that the environmental conditions of the early Earth, upon which life emerged, were verydifferent to those of today and provides essential information for guiding investigations into the origin of life in terms of realistic environmental scenarios and possible timing of the appearance of life. Microbial palaeontology investigations of well-preserved, Early Archaean rocks ~3.5to 3.3 Ga show that the earliest preserved life was diverse and widespread and suggest that it probably appeared in the Hadean, as soon asthe Earth’s surface was habitable. The extreme, anaerobic conditions characterising the early Earth, together with the ingredients of life,i.e. carbon molecules, liquid water and energy, were common on other planets and satellites in the early Solar System. Considering carbonand water-based life forms to be a cosmically frequent phenomenon, it is hypothesised that life could have emerged on some of these bodiesand that traces of its appearance may still be preserved, for instance on Mars, Europa or Enceladus. Microbial palaeontology as well asinformation gleaned from extant extremophiles and experimental data provides us with essential information about what kinds of extant orfossilised life forms to look for on another planet or satellite. Moreover, the methods evolved to study and understand the remains of fossiltraces of primitive microbial life will aid the search for life and its origins on Mars or other satellites. The perspective of returning to Earthrocks from Mars (or other samples from Europa or Enceladus?) containing potential traces of extraterrestrial life, most likely primitiveanaerobic chemotrophs, will be a challenge for microbial palaeontology that we need to start addressing now. Most importantly, it will openup the possibility of establishing the universality of life.