Moving the Waters - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 89

5
Moving the Waters
It is hard to get a proper sense of the scale of the oceans. To us they
seem just enormously deep. A thousand adult humans could—in
theory—form a column on an average part of the ocean floor by
standing on each other's shoulders—and yet the person at the top
would still not have reached more than half-way towards the sea's
surface. But now look at it on a planetary scale. The Atlantic Ocean
averages 4 kilometres deep—but is also 4,000 kilometres across. At a
thousand times wider than deep, it is therefore much, much thinner,
relatively speaking, than a pancake: it is an ultra-thin, curved liquid
skin, occupying the faintest of depressions on a planet that is
smoother—relatively speaking—than a billiard ball. At this scale, the
Earth is a ball of rock with a partially damp surface.
Yet this thin curved skin of water is in continuous movement. And
it's a good thing that it is. Returning to our familiar human perspec-
tive of seeing oceans as endlessly vast and deep, it is the movement of
the water that takes oxygen down to the very bottom of the sea floor
and keeps animal communities alive, even in the most profound
ocean trenches such as the almost 11-kilometre-deep Marianas Trench
in the Pacific Ocean. It is the movement of water, too, that brings
nutrients into the most productive fisheries in the world, such as off
the coast of Ecuador, where enormous shoals of anchovies feed