Why this matters now
Plate tectonics explains the distribution of earthquakes, volcanoes and mountain belts. UPSC tests the evolution of the theory (drift → spreading → tectonics) and the boundary types and their landforms.
Continental drift
Alfred Wegener proposed continental drift (1912): all continents were once joined in a supercontinent Pangaea (with Panthalassa ocean), which broke into Laurasia and Gondwana and drifted apart. His evidence included the jigsaw fit of coastlines, matching fossils and rock types, and ancient glaciation — but he lacked a convincing mechanism.
Sea-floor spreading
Harry Hess proposed sea-floor spreading: new oceanic crust forms at mid-ocean ridges where magma rises, and spreads outward, while old crust is destroyed at trenches. This was confirmed by palaeomagnetic stripes (symmetrical magnetic reversals on either side of ridges) — providing the missing mechanism.
Types of plate boundaries
| Boundary | Movement | Result |
|---|---|---|
| Divergent | Plates move apart | Mid-ocean ridges, rift valleys, new crust |
| Convergent | Plates collide | Subduction (trenches, volcanoes) or mountain-building (Himalayas) |
| Transform | Plates slide past | Faults & earthquakes (e.g. San Andreas) |
Significance
Plate tectonics explains the “Ring of Fire,” the formation of the Himalayas (Indian plate colliding with the Eurasian plate), the distribution of earthquakes and volcanoes along plate margins, and the slow reshaping of the Earth’s surface over geological time.
UPSC angle
Trace drift (Wegener/Pangaea) → sea-floor spreading (Hess) → plate tectonics. Match boundary types to landforms (divergent-ridges, convergent-subduction/mountains, transform-faults). Himalayas = continent-continent collision.
Frequently asked questions
What is plate tectonics?
The theory that the Earth’s lithosphere is divided into moving plates whose interactions create oceans, mountains, earthquakes and volcanoes.
Who proposed continental drift?
Alfred Wegener (1912), who argued the continents once formed the supercontinent Pangaea and later drifted apart.
What are the three types of plate boundaries?
Divergent (plates move apart), convergent (collide/subduct) and transform (slide past).
How were the Himalayas formed?
By the convergent collision of the Indian plate with the Eurasian plate, which folded the sediments of the Tethys Sea into mountains.