"From the violent beginning of the earth, it took nearly 800 mega-annum (Ma) to cool down (Hadean Eon). Igneous and metamorphic rocks from 3800 Ma to 2500 Ma (Archaean Eon) were formed principally followed by sedimentary rocks from 2500 Ma to 570 Ma (Proterozoic Eon) and mixed rock types on land as well as in the oceans from 570 Ma to the present (Phanerozoic Eon). The understanding of the origin of life and its commencement during the Archaean Eon is still in its infancy as igneous and metamorphic rocks formed at high temperatures and pressure conditions did not preserve any fossils. However, it is conjectured that the atmospheric conditions during Hadean and to some extent Archaean Eons were not conducive for the advancement/evolution of life as the atmosphere was dominated by large quantities of water vapour, carbon dioxide, sulphur and nitrogen gases and perhaps acid. However, there are some evidences that life existed, for instance in the biogenic stromatolites dated older than 3500 Ma (mostly found in Precambrian rocks). The free diatomic oxygen necessary for evolution of life gradually built up in the atmosphere with the increase in the rate of photosynthesis by the cyanobacteria (blue green algae). he life that prevailed during the Proterozoic was principally of u
Many people were worried about the possibility of a natural calamity towards the end of 2012 leading the human race to perish. Perhaps the first predictions rose from Mayan astrology â€“ chalked out in a calendar built out of stones indicating an abrupt end of the world on 21 December 2012. But, mass extinction on Earth needs to take clues from a geological perspective to be anywhere near the truth.
The authors are Asso. Professors, Ocean Science and Technology Cell and Department of Marine Geology, Mangalore University, respectively, Mangalagangotri. firstname.lastname@example.org