Red lines=faults, quakes and aftershocks visible.
Density of rock…mantle is denser than the granite of the continents and the basalt of the
ocean floor. Mantle melts to basalt, basalt melts to continent.
Mantle is SOLID.
Alfred Wegener, climatologist. Discovered fossils of tropical plants in the arctic. Theory of
continental drift, continents like icebreakers through ocean.
Sir Harold Jefferys, astronomer, mathematician, anti-continental drift. Argued that rocks
were merely too strong for any force to move it. Succeeded for forty years. What force is
strong enough to move continents?
Emile Argand, studied medicine. Supported continental drift theory. Studied Alps,
discovered that the geological formation supported the idea of continents colliding and
“folding” over one another. (Italy and Europe colliding). Found the same data in the
Himalayas…Asia and India colliding.
Arthur Holmes, physicist and geologist. 1928-rocks flow because they are heated from
below and cooled from above.
: heat rising, cold sinking. *lava lamp. Radioactive elements in the
mantle decay…as they decay, radiation (energy) is produced and takes the form
of heat. The decay heats up the rocks. Eventually sections begin to rise and the
sections above have to move out of the way…move sideways.
* Silly putty: if you push/pull it slowly, it will “flow”, if you do so rapidly, you get a crisp
break. Rocks will flow when pushed slowly.
We’re talking about geologic
time…4.6 billion years.
Rocks behave differently when they are hot or cold. When it is heated, it becomes more
elastic. When cold, stiff rocks at the surface of the earth are getting pushed around, they
initially resist and then break. The broken chunks are the plates.
Pacific is the biggest and fastest plates. North American is the second largest. Plate
boundaries are the areas where the crust has broken in response to the forces of
Many plate boundaries are in the oceans.
Appalachian and Caledonian mountains similar in age and material…north America and
northern Scandinavia once connected.
the rocks rise and reform the crust, thus pushing out the existing
rock toward the edges. The rocks, when forming, record the direction of the earth’s
magnetic field at the time.
Plates move apart, create a trough
Magma rises and creates a crust when it cools, rifting.