Life on Earth Originated Where Later Microbial Oxygenic Photosynthesis Precipitated Banded Iron Formation, Suppressing Life Diversification for 1.4 Ga

摘要

The earliest Precambrian microbial structures appear in successions with banded iron formations (BIF) suggesting genetic relationships. The hypothesis of the deep ocean origin of BIFs associated with Mid-Ocean Ridge (MOR) like features seems to have been recently supported by the discovery of peculiar microbial ecosystems with unique faunal assemblages restricted to these volcanic vents. However, new sedimentological evidence points to the accumulation of varved BIF in huge, very shallow lakes of hydrothermal-water situated on continental plates while passing through thePolar Regions, where UV radiation is minimal. The mineral-rich solutions seeped from numerous fumaroles, providing suitable conditions for chemical reactions between inorganic components, incidentally creating organic-like self-multiplying molecules long before the biologically-initiated BIF deposition. Some of these early chemoautotrophic prokaryotes developed oxygenic photosynthesis during half a year of solar illumination. The released oxygen formed iron oxides and carbonates deposited with amorphous silica (geyserite) in laminae as BIF during 3.8 - 1.9 Ga. BIF deposition consumed most of the photosynthetic oxygen for 1.4 billion years. Intensified cyanobacteria oxygenic photosynthesis during 2.4 - 2.2 Ga raised the atmospheric oxygen content (Great Oxidation Event) over the Polar Regions, forming an oxygen-ozone shield against UV radiation. It gradually extended to lower latitudes, enabling prokaryotes to leave their ecologically stable habitat and acclimatize in new ecosystems, where they diversified, leading to eukaryote evolution. The 231/2° inclination of Earth’s rotation axis differentiated the solar effect on the Polar Regions, which controlled life evolution on Earth, as well as on planet Mars (25° inclination), where life probably did not evolve beyond early prokaryotes.