[Rockhounds] WAS EARTH ONCE A WATER WORLD?

[Tim Fisher]

Oh so that's why we live in the Goldilocks Zone! 

Tim Fisher
Http://OreRockOn.com 
Email nospam at orerockon.com

 -----Original Message-----
From: Rockhounds [mailto:rockhounds-bounces at rockhounds.drizzle.com] On
Behalf Of Alan Silverstein
Sent: Friday, March 26, 2021 11:08 AM
To: rockhounds at rockhounds.drizzle.com
Subject: Re: [Rockhounds] WAS EARTH ONCE A WATER WORLD?

It seems to me the news here is, Earth once had up to 2x as much surface
water as now; not just that it used to be covered by water.  I read years
ago that the planet started out with no continents, just occasional volcanic
island arc chains, otherwise mostly water-covered.
(Of course not entirely resolved yet how the water got here from outside the
"snow line" in the early solar system.)

As plate tectonics ramped up (never mind the debate about exactly when), and
lighter "crud" rock (granitics) separated from heavier mafic (basaltic,
ocean-bottom) rocks, these arcs were "scraped off at the margins" (accreted)
by the plate-based conveyor belt to start forming the continents.  Is that a
fair summary?

Consider the Cheyenne Belt in Wyoming, the suture between the ancient craton
rocks to the NW (up to say 3600 MY) and the much younger rocks (max 1750 MY)
to the SE.  I read that except for about 40 acres in far NW CO, no CO rocks
are over 1750.  On a table at home I have, and enjoy fondling, a big chunk
of innocent-looking Sacagawea gneiss from remote Barlow Gap, WY, age ~3200
MY.

I've also read how fortunate and unlikely it is for us to have "just the
right amount" of surface water.  Too much, and it's a water-world with no
dry land for more complex lifeforms to emerge.  Too little, and it's a
desert planet instead.  If you consider how thin our shell of water is
relative to the crust and the rest, it's really remarkably Goldilocks-ish.

Cheers,
Alan Silverstein

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