Paleoarchean Era

What happened during this time?

Biological

• The oldest indirect evidence of fossil bacteria is found from Western Australian Paleoarchean rocks

  • Cyanobacteria probably present

  • 3.465 billion years ago: "11 specimens of five taxa of prokaryotic filamentous kerogenous cellular microfossils permineralized in a petrographic thin section of the Apex chert of northwestern Western Australia" (Schopf et al. 2017)

    • Microbially induced sedimentary structures (MISS) from Dresser Formation in Pilbara, Australia (3.48 Ga)

      • Although, there is evidence indicating "the black cherts formed during precipitation from silica-rich, carbon-bearing hydrothermal fluids in vein systems and vent-proximal seafloor sediments. Given the volcanic setting and lack of organic-rich sediments, we speculate that the vent-mound systems contain carbon derived from rock-powered organic synthesis in the underlying mafic-ultramafic lavas, providing a glimpse of a prebiotic world awash in terrestrial organic compounds" (Rasmussen & Muhling 2023)

      • It is probable that these structures were abiotic in origin and not evidence of early bacterial life

    • Ten-micrometre tubular microfossils found in between sand grains in a 3.4 billion-year-old sandstone.

    • The oldest stromatolites date back to about 3.43 billion years old (Wacey et al. 2011). 

      • These fossil stromatolites have layers similar to those seen in living stromatolites

      • Evidence of structures 3.46 Ga have been found to be inorganic, and not bacteria (Brasier et al. 2014): elongated filaments were created by minerals forming in hydro-thermal systems.

    • Secondary structures interpreted as simple filamentous microfossils have been recovered from the layers.

• Archaea were probably present during this time

  • South African fossils preserve fossils of archaea from a hydrothermal vent dating to 3.42 Ga (Cavalazzi et al. 2021) 

• Possible evidence of non-oxygen-generating photosynthesis (Czaja 2013)

  • Purple bacteria probably developed photosynthesis first

• The last universal common ancestor (LUCA) of all life on Earth existed during this era

Geophysical

• Continent formation begins, with increasingly larger land masses emerging from the oceans

  • Possible first super-continent, Vaalbara formed around 3.2 Ga

  • Evidence from similar sedimentary sequences on the South African Kaapvaal craton and the West Australian Pilbara craton