Eoarchean Era
The possibility of life on Earth
The Eoarchean is the first era in the Archean Eon, occurring after the Hadean Eon, and before the Paleoarchean Era.
What happens during this time?
Geophysical
The second oldest rock formation on Earth: The Isua Greenstone belt (southwest Greenland) dates to 3.8 Ga (Moorbath, 2009)
Crust formation begins in the Hadean (~3.7 Ga) and continues into the Eoarchean (Roerdink et al., 2021)
Earth is covered mostly with water
Oceans green and acidic from dissolved iron compounds
Volcanoes and volcanic islands are present, but probably no large continental masses
Plate tectonics may have been occurring as early as the early Eoarchean (Hastie et al., 2023)
Orange color to the atmosphere due to high concentrations of methane, ammonia, and carbon dioxide
Temperature mild to warm since Earth's core produced 3x as much heat as today
Sun much dimmer than today
Biological
Earth's magnetic field is not present until 3.5 Ga, thus not available to protect life from cosmic radiation
Early prokaryotes would have been able to survive due to protection by using polyphosphate manganese, to protect against oxidative stress (Dai et al., 2023)
The living bacterium Deinococcus radiodurans uses a similar mechanism to protect against radiation.
Graphite, found in the 3.95-billion-year-old rocks, shows the geochemical signature of having come from the decomposition of living organisms (Tashiro et al., 2017)
Evidence suggests prokaryotes may have evolved during this time
Early life probably used methane as an energy source
Possible evidence of stromatolites from Greenland sediments at 3.7 Ga (Nutman et al., 2016)
Microscopic filaments and tubes, which appeared to have been made by iron-loving bacteria, in rocks from the Nuvvuagittuq Supracrustal Belt in Québec, Canada (Papineau et al., 2022)
In 2017, Tiny filaments and tubes were discovered and attributed to bacteria that lived on iron, and now found encased in quartz layers in the Nuvvuagittuq Supracrustal Belt (NSB), Quebec, Canada (Dodd et al., 2017)
Further examination reveals structures such as a "stem" with parallel branches on one side that is nearly 1 cm long — as well as hundreds of distorted spheres, or ellipsoids, alongside the tubes and filaments
These structures date to 3.75 - 4.28 Ga and suggest that a variety of microbial life may have existed on primordial Earth, potentially as little as 300 million years after Earth's formation
The conditions needed to create the first protocell for life were probably alkaline hydrothermal conditions which "...not only permit protocell formation at the origin of life but actively favour it” (Jordan et al., 2019)
Another hypothesis states that the origin of life started in "fluctuating volcanic hot spring pools" (Damer & Deamer, 2020)
Above: Hematite tubes from the NSB hydrothermal vent deposits found in 2017 (Papineau et al. 2022)