Revival of the Continental Drift Hypothesis
During the 1940s and 1950s, great advances were made in our
knowledge of the sea floor and in the magnetic properties of rocks. Both
of these fields of study provided new evidence to support continental drift.
Geologists have known for over a century that a ridge exists in the
middle of the Atlantic Ocean. The Mid-Atlantic Ridge is 6,500 feet
(2,000 m) above the adjacent sea floor, which is at a depth of about
20,000 feet (6,000 m) below sea level. In the 1950s, a seismologist, a
scientist who specializes in the study of earthquakes, showed that the
global system of mid-ocean ridges was also an active seismic belt, or
zone of earthquakes. An international group of geologists proposed that
the seismic belt corresponded to a trough, or rift, system similar to the
trough known at the crest of the Mid-Atlantic Ridge. The rifts are about
20 miles (30 km) wide and 6,500 feet (2,000 m) deep. In all, the oceanic
ridges and their rifts extend for more than 37,500 miles (60,000 km) in
all the world's oceans.
