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Gya dating

Although the first continents formed during this eon, rock of this age makes up only 7% of the present world's cratons; even allowing for erosion and destruction of past formations, evidence suggests that continental crust equivalent to only 5–40% of the amount formed during the Archean.

In contrast to Proterozoic Eon rocks, Archean Eon rocks are often heavily metamorphized deep-water sediments, such as graywackes, mudstones, volcanic sediments, and banded iron formations.

Granitic rocks predominate throughout the crystalline remnants of the surviving Archean crust.

Examples include great melt sheets and voluminous plutonic masses of granite, diorite, layered intrusions, anorthosites and monzonites known as sanukitoids.

Astronomers think that the Sun had about 70–75 percent of the present luminosity, yet temperatures on Earth appear to have been near modern levels after only 500 Ma of Earth's formation (the faint young Sun paradox).The other school follows that of Richard Armstrong, who argued that the continents grew to their present volume in the first 500 million years of Earth history and have maintained a near-constant ever since: throughout most of Earth history, recycling of continental material crust back to the mantle in subduction or collision zones balances crustal growth.Opinion is also divided about the mechanism of continental crustal growth.In addition, a period of intense meteorite bombardment at 4.0–3.8 Ga may have pulverized all rocks at the Earth's surface.The similar age of the oldest surviving rocks and the Late Heavy Bombardment may not be coincidental.

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The eon's lower boundary or starting point of 4 Gya (4 billion years ago) is officially recognized by the International Commission on Stratigraphy.

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