peter jay stein, md, ma
This 54 page synopsis of the evolution
of the Earth, the origin and progression of life, and the
emergence of humans as descendants of the hominin lineage, divides the last 4.57 billion years into progressively overlapping, imagistic, time segments, to outline our place in biological existence.
Emergent Hadean Eon - 4500 - 4000 mya
Features of the Hadean eon - 4500 - 4000 mya:
1) This is the first, earliest eon, beginning with the Earth's formation, before the emergence of biological life, also a segment of what is called Precambrian times, when gravity condenses the solar dust cloud, and Earth becomes a rocky mass, followed by a molten stage, before forming a cooler, stable crust of tectonic plates.
5) As the Earth forms, molten iron and nickel sink to its core.
(the first eon of Precambrian times)
2) Thought initially to be the oldest rocks on Earth, dated from this eon, are rocks from the Acasta Gneiss Complex in Canada, dated at 4030 mya.
3) Amphibilites, found also in Northern Canada, originally on the primal Earth's ocean floor, date to 4280 mya.
4) An iron-banded rock, magnetite, also originally existing only on the ocean floor, also dates to 4280 mya, as does the 12 mile thick Earth's crust, and the oceans, themselves. Both crust and oceans exist already, within 300 million years of the Earth's birth.
6) The coldness of space cools oceans of lava, to form the Earth's crust.
7) Earth makes its full rotation in 6 hours, until a collision with a planetoid, Theia, tilts the Earth's axis, to create seasons, and further slows the Earth's rotation.
8) Fragments from the collision with Theia condense into the Moon, as water droplets from hydrated minerals within meteorites eventually cover the entire planet with oceans.