Evidence of the
earliest known life on land may have been found in 3.48-billion-year-old
geyserite and other related mineral deposits (often found around
hot springs and
geysers) uncovered in the
Dresser Formation in the Pilbara Craton. Biogenic sedimentary structures (microbialites) such as stromatolites and MISS were described from tidal, lagoonal and subtidal coastal settings that can be reconstructed from the Dresser stratigraphy as well. The rocks of the Dresser Formation display evidence of
haematite alteration that may have been microbially influenced. The earliest
direct evidence of
life on Earth may be fossils of
microorganisms
permineralized in 3.465-billion-year-old
Australian Apex
chert rocks. However, the evidence for the biogenicity of these microstructures has been thoroughly debated. Originally, 11 taxa were described from a deposit thought to be located at the mouth of a river due to certain characteristics like rounded and sorted grains. Extensive field mapping and
petrogenetic analysis has since shown the setting for the purported
microfossils to be
hydrothermal and this is widely supported. Consequently, many alternative abiotic explanations have been proposed for the filamentous microstructures including carbonaceous rims around quartz spherules and rhombs, and haematite infilled veinlets. The carbonaceous matter composing the filaments has also been repeatedly examined with
Raman spectroscopy Perhaps the most compelling argument to date is based on high spatial resolution electron microscopy like
scanning and
transmission electron microscopy. == See also ==