Geology Reference
In-Depth Information
Debating a mechanism for plate movements
While the unifying theory of plate tectonics has been well-accepted by the scientific
community, geologists have yet to agree on what, exactly, drives the movement of con-
tinental plates.
Three dominant hypotheses explain what drives plate tectonic motion. Each one relies
on the
convention
of the mantle — the movement of heated rock materials beneath
earth's crust — but each one focuses on a different piece of the cycle:
Mantle convection hypothesis:
This hypothesis proposes that heated materials in-
side the earth move up and down in a circular motion (like the wax in a lava lamp)
and the continental plates resting on this mat-erial are moved in the direction of
the circular motion.
Ridge-push hypothesis:
This hypothesis states that the creation of new rock mater-
ials along mid-ocean ridges continually pushes oceanic crustal plates upward and
outward, so that the far edges are forced into collisions with other plates.
Slab-pull hypothesis:
This hypothesis is the opposite of the ridge-push model. It
proposes that the heavy, dense outer edges of crustal plates sink into the mantle
at plate boundaries and pull the rest of the plate along with them.
And some scientists propose that the movement of crustal plates is due to a combina-
tion of all three of these driving mechanisms. Read Chapter 10 and decide what you
think is the best explanation for driving plate movements.
Moving Rocks Around on Earth's Surface
On a smaller than global scale, rocks are constantly being moved around on earth's sur-
face. Surface processes in geology include changes due to gravity, water, ice, wind, and
waves. These forces sculpt earth's surface, creating landforms and landscapes in ways
that are much easier to observe than the more expansive processes of rock formation
and tectonic movement. Surface processes are also the geologic processes humans are
more likely to encounter in their daily lives.
Gravity:
Living on earth you may take gravity for granted, but it is a powerful force
for moving rocks and sediment. Landslides, for example, result when gravity wins
over friction and pulls materials downward. The result of gravity's pull is
mass
wasting,
which I explain in Chapter 11.
