Ch 10Distribution of Oceans and Continents — Class 11 Geography, concept-first.

The chapter opens by linking back to what you have already studied — the interior of the earth. From the world map you are familiar with, you know that continents cover 29 per cent of the earth's surf…

The Atlantic Ocean’s coastlines are strikingly symmetrical. Look at the bulge of Brazil and the notch of the Gulf of Guinea on the opposite shore — they seem made for each other.

The strongest single piece of evidence for continental drift is the way the continents themselves fit together.

Wegener knew that proposing continents had moved was one thing — explaining what moved them was another.

Wegener's continental drift theory was built almost entirely on evidence gathered from the continents — fossils, rock types, and glacial deposits like tillite.

The continental drift theory had a fatal weakness: it could explain that continents moved, but not why or how.

The ocean floor is not a flat, featureless plain. Detailed research into its configuration has revealed a landscape as varied as any on land — full of relief, with mountains, plains, and deep trenches…

The ocean floor is not a flat, featureless plain. Its configuration — the shape and structure of the land beneath the sea — holds important clues about how continents and oceans have come to be distri…

The first thing to notice about earthquakes and volcanoes is that they are not scattered randomly across the globe. If you plot them on a map, they fall into distinct, narrow belts.

The story of how the ocean floor actually forms begins where Wegener's continental drift left off. After the idea of drifting continents was proposed, later studies of the ocean floor and of the magne…

The continents do not drift on their own — they ride on large, rigid slabs of the Earth's outer shell called tectonic (lithospheric) plates, and it is the movement of these plates that reshapes oceans…

The story of the continents begins at the places where the great plates of the Earth's crust are being torn apart.

At a convergent boundary, two plates move toward each other and collide. This is the destructive counterpart of the divergent boundary: instead of new crust being created, crust here is destroyed.

Transform boundaries are the places where Earth’s crust is neither created nor destroyed. Instead, two plates simply slide horizontally past each other.

The whole machinery of plate tectonics only becomes useful if we can say how fast the plates are actually moving. The ocean floor itself provides the clock.

The story of how plates move begins with a puzzle. When Wegener proposed continental drift, nearly everyone assumed the Earth was a solid, motionless body. That view has been completely overturned.

The engine that drives plate movement is the slow churning of the hot, softened mantle lying beneath the rigid plates.