The ocean bottom—a region nearly 2.5 times greater than
the total land area of the earth—is a vast frontier that even today
is largely unexplored and uncharted. Until about a century
ago, the deep-ocean floor was completely accessible, hidden (56) ______
beneath waters averaging over 3,600 meters deep. Totally without
light and subjected intense pressures hundreds of times greater (57) ______
than at the Earth’s surface, the deep-ocean bottom is a hostile
environment to humans, in some ways as forbidding and remote
as the void of out space. (58) ______
Therefore researchers have been taking samples of (59) ______
deep-ocean rocks and sediments for over a century, the first
detailed global investigation of the ocean bottom did actually (60) ______
start until 1968, with the beginning of the National Science
Foundation’s Deep Sea Drilling Project (DSDP).
Used techniques first developed for the offshore, oil and (61) ______
gas industry, the DSDP’s drill ship, the Glomar Challenger,
was able to maintain a steady position on the ocean’s surface
and drill very deep waters, extracting samples of sediments (62) ______
and rock from the ocean floor.
The Glomar Challenger’s core samples have allowed
geologists to reconstruct that the planet looked like hundreds (63) ______
of millions of years ago and to calculate what it will probably
look like millions of years in the future. Today largely on the
strength of evidence gathered during the Glomar
Challenger’s voyages, nearly all earth scientists agree with (64) ______
the theories of plate construction and continental drift that
explain many of the geological processes that shape on the (65) ______
Earth.