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.
Approach · directive: “discuss”
What it asks · Explain the plate-tectonic processes at different boundaries that create, widen, shrink or reshape continents and ocean basins over geological time.
The question has 2 parts — answer each
- Discuss the mechanism: how crustal plates move
- Discuss how these movements change the shape and size of continents and of ocean basins — at each type of boundary, with examples and evidence
Open with · From Wegener's continental drift to sea-floor spreading and plate tectonics, geology shows that the map of continents and oceans is never fixed.
Cover
- The lithosphere is broken into rigid plates moving over the asthenosphere, driven by mantle convection, slab pull and ridge push.
- Divergent margins: continental rifting (East African Rift) splits land masses; the Red Sea is a young ocean; mid-ocean ridges widen the Atlantic.
- Convergent margins: subduction at trenches consumes oceanic crust, so the Pacific basin is shrinking; island arcs form (Japan).
- Continental collision enlarges and thickens continents — the Indian plate's collision with Eurasia raised the Himalaya and Tibetan plateau.
- Transform faults (San Andreas) slide plates past each other, altering outlines without creating or destroying crust.
- Accretion of terranes and arcs adds to continental margins; over time oceans open and close (Wilson cycle) — Tethys closed, Atlantic opened.
- Evidence: fit of continents, fossils, palaeomagnetic stripes, age of ocean floor increasing away from ridges.
Close with · Continents and oceans are transient features; plate movements keep redrawing the planet's geography over millions of years.
Question: UPSC's CS (Main) 2025, GS Paper I — paper ↗. Approach: Minimalist IAS, checked 30 Sept 2026 (how we verify) — UPSC publishes no model answers. ·
Model answer · 294 words (UPSC limit 250) · Minimalist IAS
Wegener's continental drift, Hess's sea-floor spreading and plate tectonics together show that the map of continents and oceans is a snapshot of a surface that is constantly being rearranged.
Mechanism
- The rigid lithosphere is broken into plates riding on the ductile asthenosphere, moved a few centimetres a year by mantle convection, slab pull at trenches and ridge push at spreading centres.
Making and widening oceans
- Continental rifting: upwelling stretches and thins a continent until it splits — the East African Rift is dividing Africa today.
- A young ocean: the Red Sea shows the next stage, where the sea has flooded the rift.
- Sea-floor spreading: new crust forms at mid-ocean ridges, so the Atlantic widens each year and the Americas drift away from Africa and Europe.
Shrinking oceans, growing continents
- Subduction: dense oceanic crust sinks at trenches, so the Pacific shrinks while the Atlantic grows; island arcs (Japan) and volcanic ranges (Andes) form along the margins.
- Collision: when an ocean closes, continents collide and crust thickens — India's collision with Eurasia consumed the Tethys and raised the Himalaya and Tibet, enlarging Asia.
- Accretion: island arcs, seamounts and micro-continents welded onto margins (terranes) add area to continents.
Reshaping without creating or destroying crust
- Transform faults such as the San Andreas slide plates past each other, offsetting coastlines and ridges.
The long cycle and its evidence
- The Wilson cycle — rift, ocean, subduction, collision — repeats over hundreds of millions of years, assembling and breaking supercontinents such as Pangaea.
- Evidence: the jigsaw fit of coastlines, matching fossils and rock belts, palaeomagnetic stripes symmetrical about ridges, and ocean floor that grows older away from ridges.
Continents and oceans are transient features; plate movements keep redrawing the planet's geography, and today's coastlines are only a moment in that story.
Written by Minimalist IAS from facts checked at source (how we verify) — a little fuller than exam length, so every part of the question is covered; in the hall, keep the structure and trim the detail. UPSC publishes no model answers: compare your structure and coverage with this, then write your own.