Era of volcanoes and devoid of fossils
Thought to have lasted from 3.8 billion years to 2.5 billion years ago, this ancient era was mainly the period of volcanoes and rocks with less life form. Geologically this era is devoid of fossils however, few fossils have been discovered which denote existence of life in form of tiny organisms like bacteria. Various researches on all the aspects of this era bring forward some of the really interesting facts which help to unfold some of the mystery of the Earths beginning. From geological to environmental, life to rocks all are focused to reveal the nuances of this era.
Fossils of the era
The few fossils discovered were of tiny and unicellular organisms. These organisms resembled bacteria and found in arranged ways in linear colonies. The oldest fossils which were found from the sedimentary rocks of the north-west Australia were thought to be 3.5 billion years old and of chemosynthesis organisms.
Among the fossils discovered were the remnants of cyanobacterial mats or stromatolites. These bacteria were responsible for creating free oxygen in the Earth’s atmosphere. Along with the domain bacteria which were called Eubacteria, microfossils of Archaea were also discovered.
Life in the Archeozoic Era
Though it was thought that there was life in the Archeozoic Era but its prevalence is really questionable. It is thought by the geologists that life was limited and only some non-nucleated organisms existed. These organisms were single celled and known as Monera or Prokaryota. It was also thought that though organisms called eukaryotic existed in that era but they evolved without leaving fossils. Though fossils of organisms were discovered but no such fossils of viruses were found in that era.
The Archeozoic Era of volcanoes
Volcanic eruption is the major feature of this period. It was thought that at this the time volcanic activities only prevail in the Earth which caused the deposition of the igneous and sedimentary rocks.
Destruction of fossils due to significant changes in the Earth
Fossils were thought to have destroyed due to major volcanic activities which characterized the Archeozoic Era. There were also major changes in the Earth like the formation or uplift of the mountains.
Minerals of the Archeozoic Era
Among the major minerals of this era which thought to be composed from life forms of the primitive time is limestone or graphite. This fact denotes that life existed even before the Archeozoic Era.
Mineral grains like Hadean were thought to be of the Archeozoic Era but Archean are known to be the oldest rock formations belonging to this period. These rocks are thought to be from Brazil, India, Greenland, the Baltic Shield, the Canadian Shield, Southern Africa, Western Australia, and Scotland.
The first continents of the Earth were also thought to form during this era but now only 7% of the world has these rocks. Different geological activities were responsible for the destruction of these rocks.
The major surviving rocks of the Archeozoic Era are igneous and metamorphic. As it was the age of volcanic activities, the era suffered from endless lava eruptions of which some are really unusual and known as komatitie. Instances of granite rocks were also discovered by remnants of crystals in the surviving crust of Archean.
Voluminous plutonic masses and huge melt sheets of monzonites, anorthosites, layered intrusions, diorite, and granite can be taken as examples. The earth of the early part of the Archeozoic Era was thought to support a tectonic regime. There are differences of opinions among the scientists that tectonic activities were really vigorous than the present day as the atmosphere of the Earth was hotter. These result in the faster rate to recycle crustal materials. These features also thought to prevent the formation of continent and cratonisation till slowing down of convection and cooling down of the mantle.
Some groups of scientists believe that the lithosphere of the ocean was too buoyant to subduct and this causes the rarity of Archean rocks. However, research on the existence of plate tectonic activity was the matter of modern research.
Researched and differences of opinions also differed between the 2 schools of thought. According to one school there was no existence of large continents till the late of the Archeozoic Era. Another school believes that growth of the continents occurred since 500 million years ago and it is maintaining since then. Opinions also differ about the mechanism of the growth of the continental crust.
Archeozoic Era: Atmosphere
It is thought that the atmosphere of the era lacked free oxygen. According to the astronomers with 70-75% luminosity the Sun was enough puzzling. Evidence of liquid water was also found and proved by the deformation of genesis resulted from sedimentary protoloth metamorphism. It was also thought that Albedo of the Earthy was also lower in the Archeozoic Era due to cloud cover and less areas of the land.
It was also assumed that during the end of this Archeozoic Era say in c. 2500 Mya, activities of plate tectonic resembled to the modern Earth. Enough evidences of volcanic arcs, sedimentary basins, intracontinental rifts, widespread orogenic events of globe-spanning, and collisions between continent and continent were proved and suggested that assembling and destructive events of several supercontinents.
Presence of deep oceanic basins and liquid water were also known. Pillow basalts, banded iron formations, chemical sediments, and chert beds proved the existence of basins of oceans and liquid water.
Archeozoic Era: Also known as Archean this era or eon is one of the 4 major eons of the Earth. At the beginning of this eon heat flow of the Earth was 3 times higher than the present day’s flow of heat. Reason for the extra heat was thought to be the mix of remnant heat caused by accretion of planets; heat resulted due to formation of the core of the Earth and heat produced by elements of radioactivity.