Slowing Down of Seafloor Spreading

In Context

• Study shows the pace of seafloor spreading has slowed down by roughly 35 percent globally. 

About the Study

• Researchers opted for 18 ridges across the globe for this study. They analysed the magnetic records of the oceanic crust and how much oceanic crust had formed over the last 19 million years.
• Analysis showed that the seafloor is spreading at the rate of around 140 millimeters per year, down from around 200 millimeters per year compared to 15 million years ago in some places. 
  • Pace was not uniform everywhere. At places it was fast and slow at others.
• The speed of movements were  pronounced at ridges along the eastern Pacific. 
• Certain ridges in the region were roughly 100 millimeters per year slower compared to 19 million years ago, lowering the world’s average.
• Study is of the view that the factor driving the slowdown could be located in subduction zones rather than the ridges.

What is the Seafloor Spreading Phenomenon?

• It is a geological process responsible for the creation of earth crusts, the outermost shell of Earth.
• Harry Hess propounded the theory of Seafloor Spreading.
• As per the theory, the ocean floor is always moving from mid-oceanic ridge towards the trenches.
• Hot basaltic magma rises and erupts at the ridge. It cools down to become a new seafloor at this juncture.
• The newly formed seafloor at the ocean crust then gradually moves away from the ridge and its place is taken by a newer seafloor and the cycle repeats.
• In the process the older rocks move farther away from the spreading zone while younger rocks will be found nearer to the spreading zone.
• The formation of the new rocks happens at the ridge and the older rock collides with the continental crust at the subduction zone which is near to the continental crust.
• The entire process looks like a conveyor belt.

Evidences for Seafloor Spreading

• Paleomagnetism:
  • Study of Paleomagnetism gave further credibility to the continental drift hypothesis.
  • Earth’s magnetic field keeps changing the polarity. The rocks on either side of the mid-oceanic ridges attain the polarity of the earth.
  • It is observed that the alternate crustal formations are of opposite polarity moving on from ridges towards the trench. Hence paleomagnetism proves the concept of seafloor spreading.
• Deep ocean drilling:
  • Drilling at various places in the ocean has shown that the rocks near the ridges are younger while the ones nearer to trenches are older.
• Similarity of rocks:
  • Similar kinds of rocks are  equidistant on either side of the ridge in terms of constituents, age and magnetic orientation.

Why is the pace of Seafloor Spreading important for researchers?

• Having a fair idea of the pace of seafloor spreading is important because it influences sea level and the carbon cycle on the earth.
• Seafloor spreading at a faster pace means more volcanic activity and more of new crustal formations.
• It also injects greenhouse gasses into the atmosphere which have considerable impact on earth’s atmosphere.
• Basaltic rocks which are formed as a result of the process have magnetic properties. This magnetism is influenced by the Earth’s magnetic field when the magma reaches the surface and begins cooling to form the crust.
• The research is also important from the point of view of marine life at the bottom of the ocean.

Source: DTE