Origin of Earth

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Origin of Earth and Evoluation of the Environment

MODULE - 1
Environment through Ages

1
ORIGIN OF EARTH AND EVOLUTION OF THE ENVIRONMENT
We live on a beautiful planet called earth, along with a wide variety of plants, animals and other organisms. Our earth, however, is part of a vast universe. The universe is about 15 to 20 billion years old. The age of the earth is approximately 4 to 5 billion years, while human beings evolved only around 2 million years ago. In this lesson, you shall learn how the earth originated, how it got its own environment and in what ways human beings have been using the environmental resources for their welfare and development.

Notes

OBJECTIVES
After completing this lesson, you will be able to: • • • • • trace the origin of the earth; list the conditions, which make the earth a unique planet for supporting life; describe the sequence of steps in the origin and evolution of life prior to the appearance of humans; explain the term environment; enumerate the various biotic and abiotic constituents of the environment.

1.1 EARTH AS PART OF THE UNIVERSE AND THE SOLAR SYSTEM
Our earth, with all its diversity alongwith other planets and their satellites, the sun, the moon, the many galaxies (huge groups of millions of stars) form the universe. There are also countless asteroids and comets in orbit around the sun. All these are also part of the universe. It extends much farther than can be seen by the most powerful telescope. No one knows where the universe ends. 1

MODULE - 1
Environment through Ages

Environmental Science Senior Secondary Course When you look up at the sky on a clear night, you see many points of light – most of which are stars. Stars are huge balls of bright, hot glowing gases. The ‘Sun’ is also a star. It is the star nearest to earth – about 150 mk (million kilometers) away. A solar system consists of a star in the middle with a number of planets orbiting around it. The earth is a part of its solar system. It is one of the eight planets of the solar system that has the sun (a star) in the middle and the eight planets moving around it. Until recently solar system was believed to have nine planets. However, on the basis of the latest scientific assessment, Pluto, is no longer regarded as a planet of earth’s solar system. (Fig. 1.1)

Notes

Sun

Fig. 1.1: Planets orbiting the sun

1.2 ORIGIN OF THE UNIVERSE AND ORIGIN OF THE EARTH
The widely accepted theory of the origin of universe is the “BIG BANG” theory. According to this theory, universe started with a huge explosion and matter (dust and gases) filled the entire space. The temperature of the universe then, was about hundred billion degrees Celsius. Scientists believe that the big bang occurred about 15 to 20 billion years ago. The huge collection of dust and gases then began to spin. As it spun faster and faster, the centre became very hot. It became the Sun. From the edges of this ball of dust and gas, big blobs or chunks of dust broke off and formed eight ball shaped planets. This founded our solar system (Fig. 1.2). The earth broke off about 4.5 billion years ago with an explosion. It was a burning hot white mass of gas and dust. Over a long period of time, dust and gas gradually condensed to form solid rock. Such condensation and shrinking made the earth heat up so much that the rock melted into a gluey liquid. After millions of years, the outer surface of the earth or the earth’s crust cooled and formed hard rock again, just as melted chocolate or wax solidifies upon cooling. The interior of the earth is still very hot. 2

Origin of Earth and Evoluation of the Environment

MODULE - 1
Environment through Ages

Notes
Vast rotating mass of gas becomes spherical and bulges at its equator Ring of matter flung off from central mass Ring of matter cools, contracts becoming a solid planet in the oribit of the central mass which becomes sun

(a)

(b) Fig. 1.2: Formation of planets

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