Discuss how the changes in shape and sizes of continents and ocean basins of the planet take place due to tectonic movements of the crustal masses. (Answer in 250 words)

Plate tectonics explains the evolving geometry of continents and ocean basins through the movement, creation, destruction and deformation of lithospheric plates over the asthenosphere.

Creation and destruction

• At divergent boundaries, mantle upwelling creates new basaltic crust at mid-ocean ridges; seafloor spreading widens ocean basins.
• At convergent boundaries, dense oceanic crust subducts into trenches, shrinking oceans and generating arcs, earthquakes and volcanism.
• Continental collision thickens crust and forms mountain belts, as in the Himalaya, while oceanic closure can produce sutures.

Transformation of continents

• Rifting fractures continents, creates grabens and may evolve into new oceans, as in the East African Rift system.
• Transform faults laterally displace plates and offset landforms without creating or destroying crust.
• Terrane accretion, folding, faulting and uplift add material and alter continental margins.

Evidence and implications

Matching coastlines, fossil and rock correlations, palaeomagnetism, symmetrical magnetic stripes and earthquake belts support this dynamic model. Plate motions change climate-sensitive geography by altering gateways, mountain barriers and ocean circulation. Thus, continents are moving assemblies and ocean basins are temporary features in the Wilson cycle.

Keywords: lithosphere, seafloor spreading, subduction, rifting, transform fault, Wilson cycle.