Historical Geology 102
4.6 - 3.6 billion years ago
Least known Era - comprises nearly 22% of Earth's history.
What few rock that exist from this era are from the end of the era.
Individual mineral grains of zircon have been dated at 4.0-4.3 b.y.
Zircon grains were found in sedimentary rocks from Australia.
Zircon forms in intrusive igneous rocks.
Importance of these zircons is that they indicate the formation of continental crust.
Early continental crust believed to have formed from partial melting of oceanic crust and sediments at ocean-ocean convergent boundary.
Initial continental crustal plate material would have been small.
Larger plates would develop as ocean-continent and continent-continent convergence occurred.
Developement continues throughout the Archean.
Substantial continental blocks of material had developed by the end of the Eoarchean Era.
During the Eoarchean Era the surface of the Earth, and all terrestrial planets, satellites and planetesimals were subjected to intense impact bombardment.
Continuation of the accretion process.
Heaviest bombardment ends about 3.6 b.y ago. - end of the Eoarchean Era.