What went wrong when the king rode under the arch?

It was too low and knocked off his crown

How does the chain of blame unfold in the poem?

Each accused person blames another, ending with the king's own changes

Who proposed the Continental Drift Theory and when?

Alfred Wegener, a German meteorologist, in 1912.

What were Pangaea and Panthalassa?

Pangaea was the single supercontinent ("all earth") and Panthalassa was the mega-ocean ("all water") surrounding it.

Into which two masses did Pangaea first split?

Laurasia in the north and Gondwanaland in the south.

Give three pieces of evidence for continental drift.

The jig-saw fit of coastlines, rocks of the same age across the oceans, and the distribution of tillite and fossils like Mesosaurus.

What forces did Wegener suggest for drift, and why were they rejected?

The pole-fleeing force (from earth's rotation) and the tidal force (from sun and moon); most scholars considered them totally inadequate.

What is sea-floor spreading and who proposed it?

Hess (1961) proposed that new crust forms at mid-oceanic ridge crests and spreads outward, being consumed at the trenches.

How many major plates make up the lithosphere?

Seven major plates, along with several minor plates.

Name the three types of plate boundaries.

Divergent (constructive), convergent (destructive, with subduction) and transform boundaries.

What type of boundary is the Indian plate along the Himalayas?

A continent-continent convergent boundary forming a subduction zone.

What major event occurred as the Indian plate moved towards Eurasia?

The outpouring of lava forming the Deccan Traps, and later the collision (about 40–50 million years ago) that uplifted the Himalayas.

Distribution of Oceans and Continents

Class 11 Geography · Fundamentals of Physical Geography · Chapter 4

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Summary

This chapter explains how the positions of oceans and continents have changed over time. Alfred Wegener, a German meteorologist, put forward the Continental Drift Theory in 1912, proposing that all continents once formed a single mass, Pangaea ("all earth"), surrounded by a mega-ocean, Panthalassa. Around 200 million years ago Pangaea split into Laurasia (north) and Gondwanaland (south), which broke into today's continents. Evidence for drift includes the jig-saw fit of Africa and South America, matching rocks of the same age across the Atlantic, tillite (glacial) deposits, placer deposits of gold, and the distribution of fossils such as Mesosaurus. Wegener's forces (pole-fleeing force and tidal force) were considered inadequate. Post-war ocean-floor mapping revealed mid-oceanic ridges, deep trenches, young oceanic crust and thin sediments, leading Hess (1961) to propose sea-floor spreading — new crust forms at the ridges and is consumed at the trenches. In 1967 McKenzie, Parker and Morgan developed plate tectonics: the lithosphere is divided into seven major and several minor plates that move over the asthenosphere. Plate boundaries are divergent (new crust), convergent (crust destroyed at subduction zones) and transform (crust neither created nor destroyed). The movement of the Indian plate, which collided with Asia about 40–50 million years ago, caused the uplift of the Himalayas and the outpouring of the Deccan Traps.

Distribution of Oceans and Continents

Key terms

Pangaea

the single supercontinent in Wegener's theory, surrounded by the mega-ocean Panthalassa.

Tillite

sedimentary rock formed from glacial deposits, found across the southern continents as evidence of drift.

Sea-floor spreading

Hess's idea that new oceanic crust forms at mid-oceanic ridges and is consumed at trenches.

Tectonic plate

a massive rigid slab of lithosphere that moves over the asthenosphere.

Subduction zone

a convergent boundary where one plate sinks beneath another and crust is destroyed.

Mid-oceanic ridge

the longest mountain chain on earth, the site of frequent volcanic eruptions and crust generation.

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The Continental Drift Theory was put forward in 1912 by:

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Distribution of Oceans and Continents

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