Access over 20 million homework & study documents

search

STRUCTURE AND COMPOSITION OF THE EARTH

Subject

Geology

Type

Study Guide

Rating

Showing Page:
1/10
______________________________________________________________________________________
ORIGIN, STRUCTURE AND COMPOSITION OF THE EARTH
1.1 INTRODUCTION.
Welcome to Lecture 1 of this unit. To start with, stop and look around you wherever you
are. Take a look at all the things that you see around you every day. For example, the
pencil in your hand, where does the lead in the pencil come from? The room you are
probably in is made up of bricks, metal and glass; all of these things come from the Earth.
Just about everything around you that you use and see has some connection to the Earth.
The Earth beneath your feet as you stand is made up of soil, rocks and minerals. Without
the soil we would have no plants, no animals and hence no food! Many types of useful
rocks and minerals are mined from the Earth to make products that we use all the time.
Clearly, without the earth and its soils, rocks and minerals there would be no life. Do you
find what I am saying hard to believe? Well, in this lecture topic we shall introduce the
science of geology and discuss the important theories advanced for the origin of our
planet earth. You will be able to illustrate and contrast the different structural components
and composition of the earth right from its inner core to the outer surface.
At the end of this lecture, you should be able to:
a). Define what is Geology
b). State the theories advanced for the origin of the Solar system.
c). Describe the merits and demerits of the theories advanced for the origin of the
solar system.
d). Explain how the earth’s atmosphere and oceans were formed.
d). Illustrate with well labeled diagrams the structure and composition of the Earth.
e). Distinguish between Lithosphere and Asthenosphere.
f). Tabulate the distribution of chemical elements in the Earth’s crust.
1.2 WHAT IS GEOLOGY?
1
OBJECTIVES

Sign up to view the full document!

lock_open Sign Up
______________________________________________________________________________________
Geology is the study of the formation of the Earth. It is the study of rocks and minerals in
the context of the Earth we live on and the different processes taking place on the earth.
Geology is an applied science with many branches of study, for example:
Historical Geology establishes the orderly arrangement of the many physical and
biological processes occurring on Earth; Mineralogy - the study of the science of
minerals; Petrology the study of rocks in terms of their mineral composition,
occurrences, etc. Paleontology - the study of past lives of fossils.
1.3 THE ORIGIN OF THE EARTH
The Earth, together with the other eight planets Mercury, Venus, Mars, Jupiter, Saturn,
Uranus, Neptune and Pluto and their moons form the planetary system. Together with
the Sun, they form the solar system. Therefore, in order to understand the origin of the
Earth, we must first understand the origin of the solar system.
Our solar system is a group of objects in space. These objects are kept in place by the
sun’s gravitation and is basically made up of the sun, the nine planets with their moons,
and smaller bodies such as asteroids and comets.
1.4 THEORIES ADVANCED FOR THE ORIGIN OF THE SOLAR SYSTEM
There are two main theories advanced for the origin of the solar system. These are:
The Evolutionary / Uniformitarian Nebular Theory, and
The Catastrophic-Event Theory.
1.4.1 The Evolutionary / Uniformitarian Nebular Theory
2
What do you understand about the solar system?

Sign up to view the full document!

lock_open Sign Up
______________________________________________________________________________________
Its essential idea is that of a flat disc-shaped rotating cloud of gas and dust – referred to as
Nebular that gradually contracted and condensed under its own gravitational force to
form the Sun. The variants of this theory include the development of several regularly
spaced rings each of which aggregated to form a planet (see Fig. 1.1(a)). In its formation,
the earth went through a molten period as the material contracted under its own
gravitational force. Modern methods of dating rock material have shown the oldest
fragments of meteorites and moon rocks to be close to 4.6 billion years old. The
formation of the solar system is thus believed to have been substantially complete more
than 4.5 billion years ago.
1.4.1.1 Significance of The Nebular Theory
The major merit of this theory is that it is widely accepted in explaining the distribution
of planets along one plane through the Sun and the regular spacing among planets.
However this theory came into some problems in the 19
th
Century when more data about
the sizes, masses and spins of all the planets were determined. The major problem was
about the period of spins. It is argued that if the Sun and its inner planets Mercury,
Venus and the Earth which are relatively small, dense and rocky resulted from the
contraction of the rotating nebular, they should be spinning faster than the outer planets
Jupiter, Saturn, Uranus and Pluto- which are usually large, lighter and gaseous, and not
the other way round. This is not the case.
1.4.2 Catastrophic-Event Theory
This theory suggests the close approach of another condensed star to the Sun. The
gravitational forces involved would cause huge tides to be raised on the star and the Sun
until a cigar-shaped filament of stellar material became torn away from one or both and
condensed between the two stars to form planets (see Fig. 1.1(b)).
3

Sign up to view the full document!

lock_open Sign Up
User generated content is uploaded by users for the purposes of learning and should be used following Studypool's honor code & terms of service.

Anonymous
Very useful material for studying!

Studypool
4.7
Trustpilot
4.5
Sitejabber
4.4