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

What is the Nebular Hypothesis and who proposed it?

The idea that planets formed from a cloud of material around a youthful rotating sun; proposed by Kant and revised by Laplace in 1796.

What does the Big Bang Theory state about the universe's origin?

All matter existed in a tiny dense ball that exploded violently about 13.7 billion years ago, and the universe has been expanding ever since.

List the three stages in the formation of planets.

A rotating disc of gas and dust around a core, the formation of planetesimals by cohesion, and accretion of planetesimals into larger planets.

What is the process of differentiation?

The separation of earth's material into layers by density, with heavier materials (like iron) sinking to the centre and lighter ones moving towards the surface.

Name the layers of the earth from surface to centre.

Crust, mantle, outer core and inner core, with density increasing inward.

What were the three stages in the evolution of the atmosphere?

Loss of the primordial atmosphere by solar winds, degassing from the hot interior, and modification by living organisms through photosynthesis.

How old are the earth's oceans and when did life begin?

Oceans formed about 4,000 million years ago, and life began to evolve about 3,800 million years ago.

What gases dominated the early atmosphere released by degassing?

Water vapour, nitrogen, carbon dioxide, methane, ammonia and very little free oxygen.

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Chapter 2: The Origin and Evolution of the Earth — Class 11 Geography

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Chapter 2: The Origin and Evolution of the Earth

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The Nebular Hypothesis was first proposed by which philosopher?

Summary

This chapter traces ideas about the origin of the earth and the universe. Early theories include the Nebular Hypothesis of Immanuel Kant (revised by Laplace in 1796), and the modern version by Otto Schmidt and Carl Weizsacker, who held that the sun was surrounded by a solar nebula of hydrogen and helium from which planets formed by accretion. The most popular modern view of the origin of the universe is the Big Bang Theory (expanding universe hypothesis); Edwin Hubble in 1920 provided evidence that the universe is expanding. The Big Bang occurred about 13.7 billion years ago when a "tiny ball" of infinite density exploded; within the first three minutes the first atoms began to form, and after 300,000 years atomic matter arose. Stars formed from clumps within nebulae about 5–6 billion years ago, and planets developed through stages: a rotating disc of gas and dust, the formation of planetesimals by cohesion, and finally accretion into larger planets. The earth began as a barren, hot, rocky body and acquired its layered structure (crust, mantle, outer core, inner core) through the process of differentiation, where heavier materials sank to the centre. The atmosphere evolved in three stages, including degassing from the interior and modification by photosynthesis; oceans formed about 4,000 million years ago and life began to evolve around 3,800 million years ago.

The Origin and Evolution of the Earth

Key terms

Nebular Hypothesis

the idea of Kant (revised by Laplace) that planets formed from a cloud of material around a youthful, slowly rotating sun.

Big Bang Theory

the expanding-universe hypothesis that all matter began in a tiny dense ball that exploded about 13.7 billion years ago.

Light year

a measure of distance: the distance light travels in one year, about 9.461 × 10^12 km.

Planetesimals

small rounded bodies formed by cohesion of matter that later accreted into planets.

Differentiation

the process by which heavier materials sank to the centre, separating the earth into layers.

Degassing

the process by which gases and water vapour were released from the earth's hot interior to build the early atmosphere.

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the idea of Kant (revised by Laplace) that planets formed from a cloud of material around a youthful, slowly rotating sun.

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Practice quiz · The Origin and Evolution of the Earth

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The Origin and Evolution of the Earth

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