There are days when we get new research results about our Earth that are all the more exciting because of what they say could be possible on other worlds. In a new paper appearing in Science Advances, researchers led by Barbara Cavalazzi document the discovery of microfossils: the imprints of early microbes called methanogens that once dominated our world.
These microbes existed 3.42 billion years ago, during a time when Mars had oceans and Venus wasn’t all that different from Earth. Life was able to form just that fast, and this life not only pushes back the when of life but also pushes out the acceptable conditions for life.
These fossils were found in two layers of sedimentary rock collected in South Africa near the border of Eswatini and Mozambique. According to Cavalazzi: We found exceptionally well-preserved evidence of fossilized microbes that appear to have flourished along the walls of cavities created by warm water from hydrothermal systems a few meters below the seafloor. Sub-surface habitats, heated by volcanic activity, are likely to have hosted some of Earth’s earliest microbial ecosystems and this is the oldest example that we have found to date.
There are three basic things required for life: a solvent like water, a thermal gradient to drive chemical reactions, and nutrients to use in those chemical processes. In these early times, cooler seawater interacted with fluids from hydrothermal vents, creating a complex chemical soup in which these microbes thrived. It is unknown where or how life started on earth, but hydrothermal vents are considered one potential location. And Cavalazzi goes on to point out: As we also find similar environments on Mars, the study also has implications for astrobiology and the chances of finding life beyond Earth.
At this time, we haven’t identified the signs of past hydrothermal activity in the areas explored by the Curiosity and Perseverance rovers, but we do see sedimentary rock. It is unclear if either mission has the capacity to discover these kinds of fossils: their tools are generally destructive and tear samples apart to look at them chemically instead of photographically. But if there happens to be a piece of sedimentary rock that has flaked off just right then maybe? This is probably not going to happen, but it is amazing to know that someday, with better tools, there will be folks like Cavalazzi fossil hunting on Mars.
Europlanet Society press release
“Cellular remains in a ~3.42-billion-year-old subseafloor hydrothermal environment,” Barbara Cavalazzi et al., 2021 July 14, ScienceAdvances