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Wednesday, April 4, 2012

ARCHEAN EON




And the channels of the sea appeared, the foundations of the world were discovered, at the rebuking of the LORD, at the blast of the breath of his nostrils.[2 Sam.22:16]

And God called the firmament Heaven. And the evening and the morning were the second day. And God said, Let the waters under the heaven be gathered together unto one place, and let the dry [land] appear: and it was so. And God called the dry [land] Earth; and the gathering together of the waters called he Seas: and God saw that [it was] good.[Gen.1:8-9] 

For this they willingly are ignorant of, that by the word of God the heavens were of old, and the earth standing out of the water and in the water:[2 Pet.3:5]

DRY land may be something of a novelty. Until around 2.5 billion years ago our planet was almost completely covered by water. 

Today, some 28 per cent of Earth's surface is above sea level. Exactly how the ratio of land to sea has varied through Earth's history is unclear, but it is generally agreed that the amount of continental crust has increased over time. 

Now, calculations by Nicolas Flament of the University of Sydney, Australia, and colleagues suggest that Earth was a water-world until about 2.5 billion years ago, with land making up only 2 to 3 per cent of its surface (Earth and Planetary Science Letters, DOI: 10.1016/j.epsl.2008.08.029). 

As the planet cooled, clouds formed. Rain created the oceans. Recent evidence suggests the oceans may have begun forming by 4.2 Ga,or as early as 4.4 Ga.In any event, by the start of the Archean eon the Earth was already covered with oceans. The new atmosphere probably contained water vapor, carbon dioxide, nitrogen, and smaller amounts of other gases.As the output of the Sun was only 70% of the current amount, significant amounts of greenhouse gas in the atmosphere most likely prevented the surface water from freezing.Free oxygen would have been bound by hydrogen or minerals on the surface. Volcanic activity was intense and, without an ozone layer to hinder its entry, ultraviolet radiation flooded the surface.

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