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.

Spreading: oceans grow

At mid-ocean ridges, magma rises and new seafloor forms. The Atlantic has been widening since Pangaea split. Africa and South America still show the jigsaw. The Red Sea and Gulf of Aden are a young ocean. India once sat against Africa and Madagascar; the Indian Ocean opened as India drifted north. Size of an ocean basin increases at a spreading ridge.

Subduction: oceans shrink, arcs form

• Where a plate dives, seafloor is destroyed. The Pacific is ringed by trenches: Japan, Andes, Indonesia. An ocean can close. The Tethys closed as India met Asia, which is why the Himalaya and Tibetan Plateau exist and why the Indian continent’s northern edge is crumpled. Continents rarely subduct wholesale because they are buoyant, but they change shape: India is still pushing into Asia, so the collision zone thickens and shortens.

Rift, transform, and the map in motion

East Africa’s rift may split a new sea. Transform faults (San Andreas) slide plates sideways and change coast shape without creating much new crust. Supercontinent cycles assemble and break worlds: Pangaea is the famous last assembly.

• Consequences for the planet’s look: Himalayan rivers reverse or capture; climate changes when mountains rise and when seaways open (think of the Drake Passage and Antarctic cooling). Islands appear as arcs. The Mediterranean is a leftover of Tethys.

Nothing here is a human lifetime. The explanation of “changes in shape and sizes” is plate kinematics plus time.