How the Earth's Continents Move

Understanding Plate Tectonics

Nov 12, 2009 Jeri Schott

The heat at the center of the earth is responsible for the slow movement of the continents.

The mechanics of this process are accurately explained in Visualizing Geology by B.W. Murck and B.J. Skinner (2008, John Wiley & Sons). The pioneering earth scientist, Alfred Wegener (1880-1930) postulated that the seven earth continents once sat as one land mass. He theorized the mass broke away over several thousands of years but even “Wegener could not explain how this could happen”. Geologists now call Wegener’s theory plate tectonics and define margins along which the plates move.

Convergent and Divergent Margins on Earth

Land masses move along fractures in the earth’s crust. In a convergent margin, the plates move toward one another. A noted convergence is that of subduction. In the subduction zone, the lithosphere (rocky earth layer) slides beneath the asthenosphere (weak rock beneath lithosphere) and oceanic trenches appear. Subduction must involve one submerged layer meaning it cannot occur between two buoyant land masses.

Land layers move away from one another in a divergent margin. A transform fault is a type of divergent margin. The San Andreas Fault in California, an exception within this fault type, occurs on the surface and not beneath water.

The gradual slipping of plates along fractures may cause horizontal or vertical movement at the surface of the affected area. Divergent margins typically initiate horizontal motion. Convergence likely causes vertical movement. If he was alive today, Wegener might conclude that an awesome source of power is required to move solid rock.

The Heat Within the Earth's Core

A temperature of 116 °F forces people inside, into the pool, or beneath a shade tree for relief. Even the time after sunset offers little reprieve after a day of such extreme heat. Consider then the temperature of the earth’s center is 5000 °F. Heat released from the center of the earth results in plate movements. What exactly happens between the heat release and the quake?

Beyond the searing, solid inner earth core is the liquid outer core and the mantle. The mantle contains the mesosphere, asthenosphere, and lithosphere. The core discharges heat through the mesosphere, asthenosphere, and finally settles in the lithosphere but not without effect. The heat penetrates the asthenosphere which is a ductile earth layer. The asthenosphere adjusts, causing slight movement of the lithosphere or plates. Consider a marshmallow heated with a graham cracker on top. The marshmallow softens and the cracker shifts, sometimes cracks. So it is with the asthenosphere and lithosphere respectively.

As burning rocks return to the earth’s cooler surface, colder materials sink toward the heat. Plate shift involves a consistent cycle but perfect realignment of risen plates is impossible. Often, the earth layers stick to one another during readjustment. Pressure and energy build as passing plates deny each other movement. When finally let go, the abrupt vibration has a capacity to carry on for miles and can end in destruction. The outcome depends on conduction elements. The release of heat is the primary cause of plate tectonics as well as earthquakes. The process is not a simple or quick progression.

Reference

Murck, B.W. & Skinner, B.J. (2008). Visualizing Geology. New Jersey: John Wiley & Sons

The copyright of the article How the Earth's Continents Move in Geology/Ecology is owned by Jeri Schott. Permission to republish How the Earth's Continents Move in print or online must be granted by the author in writing.

Earth Continents

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