Hadean Eon
Explanation:
The Hadean rocks are comprised of early earth forming rocks where there is the absence of fossils. It is because life did not originate during the time of Hadean. It originated only after the end of this eon and in the Archean eon, about 3.6 billion years back, the first life form appeared on earth. It was possible because of the favourable condition that supported the existence of life on earth. It was found to be present in the sedimentary rocks.
Further explanation:
The Hadean eon belongs to the Precambrian time during which the earth started to form. It started about 4.6 billion years to 4 billion years back. This eon is characterised by the heavy bombardment and continuous impacts of rocky materials that led to the formation of the core and the mantle over a due course of time. This further developed the crust and eventually created the atmosphere of the earth that provided the essential conditions for the existence of life.
The fossils are defined as the remnants of the ancient plants and animals that were buried millions of years back. These are formed under certain conditions like they should be comprised of hard parts and should be immediately buried under the sediments, detaching from the oxygenated environment and are subjected to extreme pressure and temperature condition as a result of which fossilisation process takes place.
These fossils are found in sedimentary rocks as they are soft and able to preserve under extreme conditions. They are not found in the igneous and metamorphic rocks because they get damaged when they come in contact with the magma and because of the extremely high temperature and pressure condition.
Learn more:
1. Hadean eon (answer by Joebiden1)
2. Earth formation, origin of life and geological time scale (answer by Lucic)
Keywords:
Eon, Hadean, Archean, Sedimentary rocks, fossils, fossilization, oxygenated environment, igneous rocks, metamorphic rocks
