[Rockhounds] WAS EARTH ONCE A WATER WORLD?

[Alan Silverstein]

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