Sea floor spread theory and Evidence Upsc

Seafloor spreading definition

The formation of new areas of oceanic crust happens by the upcoming magma at mid-ocean ridges and its outward movement on either side.

The constant eruption by volcanoes at the crest of oceanic ridges causes cracks or ruptures of the oceanic crust. Then lava is filled into the cracks of oceanic ridges. This pushes the oceanic ridge on either side. As a result ocean floor spreads.

Sea floor spread theory and Evidence Upsc
Seafloor Spreading diagram By Muller, R.D., M. Sdrolias, C. Gaina, and W.R. Roest (2008) Age, spreading rates and spreading symmetry of the world’s ocean crust, Geochem. Geophys. Geosyst., 9, Q04006, doi:10.1029/2007GC001743. – File:Age of oceanic lithosphere.jpg Source; National Geophysical Data Center, National Oceanic and Atmospheric Administration, U.S. Department of Commerce,, CC BY 3.0,

The seafloor spreading hypothesis was proposed by Hess in 1961. As per his hypothesis the spreading forms a successively younger ocean floor. The flow of material brings migration or drifting apart the continents. Seafloor spreading occurs at the divergent plate boundaries, as the tectonic plates slowly move away from one another.

The heat from the mantles convection current makes the crust less dense. As a result, the less dense material rises to form an elevated area or mountain on the seafloor. That makes the crust cracks and again filled by lava and move apart.

Seafloor spreading and continental drift are believed to be caused by mantle convection.

Evidence of seafloor spreading upsc

All along the mid-oceanic ridges, volcanic eruptions are common and bring a large amount of lave to the surface. The rocks that are equidistant on either side of the crest of mid-oceanic ridges show great similarities in terms of age, chemical, and magnetic properties.

The rocks that are closer to the mid-oceanic ridges have normal polarity, these are the youngest. But the age of rocks increases as one moves away from the crest.

The age of the rocks of ocean crust (Age: About 200 million Years) is much younger than the continental rocks(3200 Million Year). The sediments on the ocean floor are unexpectedly very thin. Nowhere the sediments column found were older than 200 million years.

The deep trenches have deep-seated earthquakes occurrences on the other hand the areas of the mid-oceanic ridge, have shallow depths. These facts and a detailed analysis of magnetic properties of the rocks on either side of the mid-oceanic ridge led Hess (1961) to propose his hypothesis, known as the “seafloor spreading”.

Hess argued that constant eruptions at the crest of oceanic ridges cause the rupture of the oceanic crust and the new lava wedges into it, pushing the oceanic crust on either side. The ocean floor thus spreads.

The younger age of the oceanic crust as well as the fact that the spreading of one ocean does not cause the shrinking of the other, made Hess think about the consumption of the oceanic crust. He further maintained that the ocean floor that gets pushed due to volcanic eruptions at the crest, sinks down at the oceanic trenches and gets consumed.


We have discussed the definition of Ocean Floor Spreading, its causes, and evidence that support it.

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* * All the Notes in this blog, are referred from Tamil Nadu State Board Books and Samacheer Kalvi Books. Kindly check with the original Tamil Nadu state board books and Ncert Books.
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