SETI [Fwd: [seti] Was Earth a giant ocean from the start?]


Robert Owen (rowen@technologist.com)
Wed, 29 Sep 1999 14:41:29 -0400


Larry Klaes wrote:

> From: Larry Klaes <lklaes@bbn.com>
>
> HAS EARTH BEEN WATERY PLANET RIGHT FROM THE START?
>
> >From Andrew Yee <ayee@nova.astro.utoronto.ca>
>
> [http://helix.nature.com/nsu/990930/990930-4.html]
>
> Monday, September 27, 1999
>
> Water bath
> By PHILIP BALL
>
> Prevailing opinion has it that the oceans came from space after the
> Earth was formed 4.6 billion years ago. It has been thought that the
> impact of icy bodies -- comets or debris left over from the formation
> of the planets -- on the early Earth deposited the water that now fills
> the ocean basins. But an alternative idea is that the material that
> went into the formation of our planet was already wet.
>
> All the planets formed from clumps of matter that condensed within the
> cloud of gas and dust surrounding the new-born Sun. Collisions between
> these clumps were constantly happening throughout the early Solar
> System, and the debris that resulted then stuck together under its own
> gravity. The lumps within the inner Solar System may have been dry and
> rocky, with the volatile constituents -- the gases and liquids in the
> atmospheres of Venus, Earth and Mars -- added by later collisions.
>
> But did it have to be this way, or could the initial clumps have
> themselves contained water? If so, it seems likely that most of this
> water would have been dissolved in a pole-to-pole ocean of molten rock
> -- magma -- when the Earth was still young. Such a magma ocean is
> expected to have resulted from the massive collision widely believed to
> have split off the material that formed the Moon. As the magma cooled
> and froze, the water would then have come steaming out into the
> atmosphere, later to condense into oceans.
>
> As the Earth cooled, it separated into an iron-rich core and a rocky
> mantle -- like slag separating from the molten metal in an iron
> smelting furnace. Other metals similar to iron, such as cobalt, nickel
> and tungsten, would have dissolved to different extents in the magma
> ocean and the molten iron below. Geophysicists can account for the
> known distribution of such metals between the present core and mantle
> based on the way that they partition between iron and molten, dry rock
> -- but how would water affect this picture?
>
> Kevin Righter and Michael Drake from the University of Arizona have now
> measured this partitioning behaviour, with water present, at the high
> temperatures and pressures appropriate to the juncture between an iron
> core and a magma ocean. They find that small amounts of water, as
> postulated for a "wet" accretion of the Earth, do not undermine the
> existing explanation for the distribution of metals between core and
> mantle.
>
> What is more, they say, water present from the very beginning of
> Earth's history can help to explain why there is so much iron oxide in
> the mantle today: the oxide is formed by the reaction of water with hot
> iron. It is not easy otherwise to account for how the iron oxide got
> there.
>
> So the new measurements, reported in the journal Earth and Planetary
> Science Letters (September), lend support to the idea that the Earth
> has been a watery planet right from the start.
>
> Macmillan Magazines Lt

=======================
Robert M. Owen
Director
The Orion Institute
57 W. Morgan Street
Brevard, NC 28712-3659 USA
=======================



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