But what of this environment into which, armed with the atom, we plunge
with such enthusiasm and expectations? A portrait is in order, which
must be brief, for not all the books ever written about the sea have yet
described it fully.
The world ocean covers 70.8% of our planet. It contains 324,000,000
cubic miles of seawater. Living in it are upwards of a million different
species of plants and animals. They range from one-celled organisms that
can only be seen with a microscope to the largest creature ever to have
lived on this earth—the giant blue (or sulfur-bottom) whale, captured
specimens of which have exceeded 90 feet in length and 100 tons in
weight.
The ocean’s depth ranges from 600 feet or less above continental shelves
to more than 35,000 feet at the Marianas Trench. The mean depth is
12,451 feet. Sea bottom topography includes wide plains, the world’s
longest mountain range, steeply rising individual truncated peaks called
_guyots_ (pronounced gee-ohs), gentle slopes, narrow canyons, and
precipitous escarpments. Mountains higher than Everest rise from the
ocean floor and never pierce the surface.
[Illustration: _Underwater mountain traced by the Woods Hole
Oceanographic Institution echo sounder in the Caribbean area. Depth
is determined by the time it takes the sound emitted by the
instrument to go to the bottom and return to the surface._]