For a long time, the best way to study geology and marine life was
with dredges. A dredge is a large weighted metal or wooden box that is
open at one end. Like the sounding line, a dredge is thrown off of
a ship. It sinks to the sea floor. The motion of the ship pulls the
dredge. It acts like a shovel, scooping up marine life and rocks. This
allowed early scientists to learn what was down there. However, dredges
are not very precise. Because they could not see the bottom, scientists
could not tell exactly where their samples came from.
Marine geologists have uncovered many secrets of the deep by looking
at slices of the bottom or sediment cores. They have discovered
that the ocean floors are relatively young. Rocks that are older than
Cretaceous are very difficult to find throughout the world’s oceans.
Discovering the features and plotting all this information on maps, led
to the confirmation of the patterns produced by plate tectonics. The
ridges, seamounts, trenches, fractures, and continental margins all
correspond to the idea of plates moving within the crust and upper