Earth’s habitability in a planetary framework: The Archean rock record

Abstract

This study briefly synthesizes geochemical and isotopic evidence of co-evolution of Earth’s surface, atmosphere, oceans and biosphere from Hadean to Archean geological records.  Impact induced Hadean tectonics, emergence of oceans and the reducing atmosphere created conditions favourable for the initial biological processes. Intense volcano-hydrothermal activity and tectonism were responsible for nutrient supply and circulation, supporting microbial life. Geochemical trends of bio-essential elements such as Fe, Mn, Mo, P, Ni, Co, and U indicate a strong relationship between elemental cycling and early life processes. Archean passive margin sedimentary rocks such as stromatolitic carbonates, banded iron formations (BIFs), Manganese deposits, and carbonaceous shales present in the greenstone belts of Dharwar Craton preserve biosignatures indicating ancient microbial activity under varying redox conditions of early Earth. Higher thermal state of the Archean Earth led to intense volcano-exhalative activity, released Fe-Mn, gold along with other sulphides creating alkaline to acidic, reduced and chemically enriched oceans favouring cyanobacterial growth. Oxygen released due to microbial activity deposited Fe and Mn as oxides at shallow shelves.  These processes detoxified the ocean, rendering the planet habitable for the growth and diversification of advanced life forms. Decayed organic matter contributed to the deposition of carbonaceous shales at the deeper ocean with δ¹³C_org of -38.8‰ to -8‰ VPDB, coinciding with associated BIFs (-28.5‰) and Mn formations (-26.2 to -23.2‰ VPDB) reflecting on significant biological influence. Geological similarities of Mars, Venus with Earth suggest that life supporting conditions may have existed for a short time on these terrestrial planets.