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Donna Gonzales, age 14, of Albany, New York, for her question:

What is meant by the lithosphere?

The litho part of this word means "stone" and the sphere refers to the shape of our globe. We know, of course, that our planet is built in layers, somewhat like neatly enfolded onion skins. The lightest sphere is the gaseous atmosphere above the solid planet. The hydrosphere is the liquid sheath of water that fills the oceans, permeates the land and links the surface with the weathery atmosphere. The lithosphere is the solid rocky layer that underlies the oceans and humps up to form the dry land.

Most people refer to the lithosphere as the earth's crust    the special study of geologists, geographers and other earth scientists.. It so happens that recently this entire study was shaken by some startling new theories.. For several generations,. earth scientists probed the restless upheavals of the crust. They were certain of some of the causes and almost certain of others. Then a team of researchers discarded these previous theories, suggested different ones and supported them with masses of new evidence.

These new theories do not challenge the size of the earth's crust, or its geological ingredients. We still may say that the lithosphere is made from about 2,000 different stony and metallic minerals.. Nobody will contradict us if we say that the average thickness of the lithosphere ranges from about 20 to 40 miles. But let's wait for more proof before we explain the dynamic forces that cause crustal upheavals.

The new theory suggests that continents and ocean floors are numerous mobile rocky plates, pushing and shoving each other in various directions. On the continents, the cracks between the plates are unstable faults and numerous small ones connect to form major earthquake faults. The restless rafts are maneuvered by weather from above and planetary forces from below. All the plates of the lithosphere float, so to speak, on or partly submerged in the more pliable mantle that is subject to goodness knows what dynamic forces from deeper within the planet.

But the real surface action is in the sea beds. There, we are told, mantle material constantly oozes up through the cracks, spreads the crustal plates apart and seals the seams. The theory suggests that the seabeds are spreading and have been spreading, perhaps since the infant earth formed its first solid crust.

A lot of evidence has been gathered to support this new theory and it explains several mysteries of the past. For example, it explains how a spreading seabed can widen cracks between continental plates and push the land masses apart. This could provide the final proof that the land masses separated from an ancient single continent. The spreading seabeds cracked them and shoved them apart.

This fantastic story sounds somewhat unsettling. But remember, the lithosphere was always restless and its gradual changes were hardly noticeable through the centuries. The new theory may explain its activities more accurately. But it cannot speed up the process and the solid old lithosphere will continue to provide us with a dependable living surface.

 

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