Evaluating the Evidence for Continental Drift

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Evaluating the Evidence for Continental Drift

There are several pieces of evidence certifying the existence of

continental drift. They include mid oceanic ridges, fitting of

continents, similarities of fossils on different continents and rock

matches.

The mid-oceanic ridges rise 3000 meters from the ocean floor and are

more than 2000 kilometres wide surpassing the Himalayas in size. The

mapping of the seafloor also revealed that these huge underwater

mountain ranges have a deep trench, which bisects the length of the

ridges, and in places is more than 2000 meters deep. Research into the

heat flow from the ocean floor during the early 1960s revealed that

the greatest heat flow was centred at the crests of these mid-oceanic

ridges. Seismic studies show that the mid-oceanic ridges experience an

elevated number of earthquakes. All these observations indicate

intense geological activity at the mid-oceanic ridges.

Periodically, the Earth's magnetic field reverses. New rock formed

from magma records the orientation of Earth's magnetic field at the

time the magma cools. Study of the sea floor with magnetometers

revealed "stripes" of alternating magnetisation parallel to the

mid-oceanic ridges.

This is evidence for continuous formation of new rock at the ridges.

As more rock forms, older rock is pushed farther away from the ridge,

producing symmetrical stripes to either side of the ridge. In the

diagram to the right, the dark stripes represent ocean floor generated

during "reversed" polar orientation and the lighter stripes represent

the polar orientation we have today. Notice that the patterns on

either side of the line representing the mid-oceanic ridge are mirror

images of one another. The shaded stripes also represent older and

older rock as they move away from the mid-oceanic ridge. Geologists

have determined that rocks found in different parts of the planet with

similar ages have the same magnetic characteristics.

The deepest waters are found in oceanic trenches, which plunge as deep

as 35,000 feet below the ocean surface. These trenches are usually

long and narrow, and run parallel to and near the oceans margins.

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