Published online by Cambridge University Press: 22 October 2009
I find no traces of a beginning
(James Hutton)In the following four chapters, we deal with the development of the continental crust on the Earth. The history of this planet, except for the past 200 Myr, is contained almost entirely in the continental crust that is subject to so many factors (erosion, tectonic activity, differentiation, metamorphism, volcanism, break-up and re-accretion among others) that it is surprising how good the record is. We begin with that dark period from which no rocks have survived. This however has not prevented, but rather encouraged speculation about the nature of the crust in that remote epoch. This, the so-named Hadean Eon, extends for several hundred million years, from the formation of the Earth to the first known occurrence of a preserved rock record, a period of time comparable to the extent of the Phanerozoic.
The Hadean crust and mantle
What indeed was the nature of the crust of the Hadean Earth? Extensive searches have failed to reveal rocks older than somewhere between 3850 and 4030 Myr. The only earlier remnants that have survived to record the existence of Hadean surface rocks are some relict detrital zircon crystals up to 4100 Myr in age, with a handful as old as 4363 Myr, that are found in younger sedimentary rocks in the Jack Hills in Western Australia.
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