Origin of Life on Earth

Modern scientists refer to the origin of life as a kind of chemical reaction, which first generated complex organic molecules and assembled them. This assemblage was such that they could duplicate themselves converting inanimate matter into living substance. The record of life that existed on this planet in different periods is found in rocks in the form of fossils. The microscopic structures closely related to the present form of blue algae have been found in geological formations that are much older than these were some 3,000 million years ago. It can be assumed that life began to evolve sometime 3,800 million years ago. The summary of evolution of life from unicellular bacteria to the modern man is given in the Geological Time Scale on last page.

In the Solar System, the Earth has a special relationship with the Sun and the Moon. The Earth revolves around the Sun, and the Moon revolves around the Earth. The Earth also rotates on its axis.

These motions of the Earth cause days and nights, seasons, tides, eclipses, etc.

7.2.1. Day and Night

When the earth rotates on its own axis, only one portion of the earth’s surface comes into the rays of the sun and experiences daylight. The other portion which is away from the sun’ rays will be in darkness. As the earth rotates from west to east, every part of the earth’s surface will be brought under the sun at some time or other, a part of the earth’s surface that emerges from darkness into the sun’s rays experiences sunrise. Later, when it is gradually obscures from the sun is in fact, stationary and it is the earth which rotates. The illusion is exactly the same as when we travel in a fast- moving train. The trees and houses around us appear to move and we feel that the train is stationary.