Earth Sciences

When you have read this chapter you will have been introduced to:

• the formation and structure of the Earth


• rocks, minerals, and geologic structures


• weathering


• how landforms evolve


• coasts, estuaries, and changing sea levels


• solar energy


• albedo and heat capacity


• the greenhouse effect


• evolution, composition, and structure of the atmosphere


• general circulation of the atmosphere


• ocean currents and gyres


• weather and climate


• ice ages and interglacials


• climate change


• climatic regions and plants

6. Formation and structure of the Earth

Among the nine planets in the solar system, Earth is the only one which is known to support life. All
the materials we use are taken from the Earth and it supplies us with everything we eat and drink. It
receives energy from the Sun, which drives its climates and biological systems, but materially it is
self-contained, apart from the dust particles and occasional meteorites that reach it from space
(ADAMS, 1977, pp. 35–36). These may amount to 10000 tonnes a year, but most are vaporized by
the heat of friction as they enter the upper atmosphere and we see them as ‘shooting stars’. At the
most fundamental level, the Earth is our environment.

The oldest rocks, found on the Moon, are about 4.6 billion years old and this is generally accepted to
be the approximate age of the Earth and the solar system generally. There are several rival theories
describing the process by which the solar system may have formed.^1 The most widely accepted
theory, first proposed in 1644 by René Descartes (1596–1650), proposes that the system formed
from the condensation of a cloud of gas and dust, called the ‘primitive solar nebula’ (PSN). It is now
thought this cloud may have been perturbed by material from a supernova explosion. Fusion processes
within stars convert hydrogen to helium and in larger stars go on to form all the heavier elements up
to iron. Elements heavier than iron can be produced only under the extreme conditions of the supernova
explosion of a very massive star, and the presence of such elements (including zinc, gold, mercury,
and uranium) on Earth indicates a supernova source.

As the cloud condensed, its mass was greatest near the centre. This concentration of matter comprised the
Sun, the planets forming from the remaining material in a disc surrounding the star, and the whole system

2

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