Sea Floor Spreading

• It was realized that all along the mid oceanic ridges, volcanic eruptions are common and they bring huge amounts of lava to the surface in this area.
• The rocks equidistant on either side of the crest of mid-oceanic ridges show remarkable similarities in terms of period of formation, chemical compositions and magnetic properties.
• The age of the rocks increases as one moves away from the crest of the Ridges.
• The ocean crust rocks are much younger than the continental rocks. The age of rocks in the oceanic crust is nowhere more than 200 million years old while some of the continental rock formations are as old as 3,200 million years.
• The sediments on the ocean floor are unexpectedly very thin.
• The deep trenches have deep-seated earthquake occurrences while in the mid oceanic ridge areas, the quake foci have shallow depths.
• These facts led Harry Hess to propose his hypothesis, known as the “sea floor spreading”. The force of the Sea floor spreading was found to be Convective current as postulated by Arthur Holmes.
• Magma continuously wells upwards at the mid-oceanic ridges producing currents of magma flowing in opposite directions and thus generating the forces that pull the sea floor apart at the mid-oceanic ridges.
• As the ocean floor is spread apart, cracks appear in the middle of the ridges allowing molten magma to surface through the cracks to form the newest ocean floor. Here, new crust is generated.
• As the ocean floor moves away from the midocean ridge eventually comes into contact with a continental plate at convergent boundary, subducted underneath the continent and the crustal mass is consumed here.
• Finally, the lithosphere drives back into the asthenosphere where it returns to a heated state.

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