Explain the concept of Sea Floor Spreading and the facts that support this theory.
Structure:
Introduction: (upto 30 words) Mention the context of the concept of Sea Floor Spreading.
Body: (upto 100 words) Explain the theory and the evidences used to support the theory.
Conclusion: (upto 30 words) Conclude by pointing out that the Sea Floor Spreading theory and Continental Drift theory formed the basis for Plate tectonics later.
Supporting Points:
The Seafloor spreading theory was proposed explaining the distribution of Oceans and continents. The idea that the seafloor itself moves (and carries the continents with it) as it expands from a central axis was proposed by Harry Hess.
According to this theory, the intense heat generated by radioactive substances in the mantle (100-2900 km below the earth surface) seeks a path to escape, and gives rise to the formation of convention currents in the mantle.
Wherever rising limbs of these currents meet, oceanic ridges are formed on the sea floor and wherever the failing limbs meet, trenches are formed.
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.
Seafloor spreading helps explain continental drift in the theory of plate tectonics. When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere.
Basaltic magma rises up the fractures and cools on the ocean floor to form new sea floor.
Older rocks will be found farther away from the spreading zone while younger rocks will be found nearer to the spreading zone.
Evidences:
The mapping of the ocean floor and Paleomagnetic studies of rocks from oceanic regions revealed the following facts :
Volcanic eruptions are common all along the midoceanic ridges and they bring huge amounts of lava to the surface in this area.
The rocks equidistant on either sides of the crest of mid-oceanic ridges show remarkable similarities
Rocks closer to the mid-oceanic ridges are normal polarity and are the youngest.
The age of the rocks increases as one moves away from the crest.
The deep trenches have deep-seated earthquake occurrences while in the midoceanic ridge areas, the quake foci have shallow depths.
It was on the basis of the continental drift theory, theory of sea floor spreading, that the theory of Plate Tectonics was formulated—first outlined by Morgan in 1968.
