Ocean Forms - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 60

continents are largely overlain by younger rocks, and because older
mountain belts can be refashioned as new ones grow. Nevertheless,
patterns have been discerned—although (of course) different stud-
ies have reached different conclusions. Some models of continental
evolution seem to show more or less steady growth, while others
suggest that continents grew (and ocean basins therefore shrank) in
distinct pulses.
The Balance of Water
Given that there may have been, on that early Earth, more ocean crust
and less continental crust, how might that affect the oceans that filled
them? The evidence of the rocks hints that, even in those early days,
the seas might have covered a good deal of the continents. That might
be explained if the ocean floor was generally higher (relative to the
continents) on a young Earth, to help the waters spill over on to the
higher ground. However, if the 'precursor tectonics' operated more
sluggishly, it has been suggested 46 that the ocean floors might have
been lower and deeper than now. And if that was the case, to help
flood the continents there may have been more water in the ocean
basins—perhaps as much as twice today's amount.
We need to think, therefore, about where that ocean water might
have disappeared to .
We have been speaking so far of the ocean basins: the receptacles,
as it were, of Earthly water—as if the surface of our planet was noth-
ing other than a succession of different types and shapes of bowls to
fit that water into. That isn't quite the case. There is also a balance of
water between that at the surface and that which lies very deep in the
Earth, dissolved in the rocks of the mantle and making those rocks
flow more easily in the slow subterranean currents that drive plate
tectonics (we will leave for now the question of any continued trans-
fer of water from the surface to outer space).