The term Archean means “ancient” and was originally used to refer to the oldest known rocks which are approximately 3.8 billion years old. It was around that time the surface of the Earth changed from molten material into rocks and continental plates at which point Earth’s geological history began. While much of the original Archean terrain has been destroyed through erosion and plate tectonics, Archean rocks are known from Greenland, Scotland, India, Brazil, western Australia, and southern Africa.
Tectonics and Paleoclimate
Within the initial 100 million years of the Archean Eon, the Earth's crust had significantly cooled. The atmosphere was primarily composed of methane, ammonia, and other gases which eventually gave way to volcanic gases including nitrogen, hydrogen, carbon, and possibly low levels of oxygen. Water vapor was becoming abundant and the first oceans were forming. By the end of the Archaean plate tectonic activity may have been similar to that of the modern Earth. There is evidence of volcanic arcs, intracontinental rifts, continent-continent collisions and widespread globe-spanning structural deformation events suggesting the assembly and destruction of one and perhaps several supercontinents.
To date, there is no evidence of plant or plant-like life during the Archeon Eon.
Flora & Fauna
It was early in the Archean that life first appeared on Earth. A complex set of chemical reactions in these early oceans transformed carbon-containing molecules into simple, single-celled life forms. These early life forms arose roughly 3.5 billion years ago and consisted of bacteria which was essentially the only life form for more than a billion years. The Archean coast was home to mounded colonies of photosynthetic bacteria called stromatolites the fossils of which have been found South Africa and western Australia. Microfossils of non-nucleated, single-celled archaeans have also been identified in the later stages of the Archean Eon. Thus far, no fossil evidence has been discovered for ultramicroscopic life such as viruses. By the end of the Archean, the first photosynthesizing organisms had evolved and begun to produce oxygen which was released into the oceans and atmosphere.
Meteorite Impacts on Earth
I included a list of meteorite impacts relevant to this time period as a point of reference since many of the explanations for mass extinctions throughout Earth’s history include meteorite impact(s) as a possible cause. The meteorite impact information below was obtained from the ‘Earth Impact Database’ maintained by the Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick, Canada ( www.passc.net/EarthImpactDatabase).