Asteroid impact responsible for melting, recasting of Earths crust

December 11th, 2007 - 2:51 pm ICT by admin  

Washington, Dec 11 (ANI): A University of Minnesota geologist has suggested that the continuous overturning, melting and re-casting of Earth’s crust may have started with a massive asteroid impact in Earth’s infancy.
If true, this conclusion could throw light on how and why plate tectonics did or did not get started on other worlds in our solar system and beyond, claims geologist Vicki Hansen.
“Everyone argues about when (plate tectonics) starts, but never asks about outside processes,” Discovery News quotes Hansen, as saying.
“As geologists, we don’t even consider impacts beyond perhaps causing one or two mass extinction events much later in Earth’s history. We should at least ask the question,” she said.
In an article that appears in the December issue of the journal Geology, Hansen opines that tectonic plates were set in motionover three billion years ago, when the densest materials sank to the core, and the lightest materials settled into an outermost crust, also known as the “Felsic” crust.
Meanwhile, out in space, the solar system was still pretty full of bits and pieces of failed planets — asteroids galore.
Hansen says that if one of those of sufficient size slammed down on one of the warmer, weaker parts of young Earth’s felsic crust, it could punch a hole and trigger melting in the mantle, and an eruption.
This erupted lava from the mantle would have solidified and become Earth’s first heavier, more brittle “mafic” crust, and this is the sort of crust being created today at ocean spreading centres as well as pouring out of the Hawaiian Islands volcanoes, she says.
“Once started, it’s an on-going process,” said tectonics researcher Peter Cawood of the University of Western Australia.
“It certainly gives our ideas about sub-duction initiation a shock,” Cawood told Discovery News. (ANI)

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