It is now known that all the inner planets of the sun’s orbit, namely, Mercury, Venus, Earth and Mars, are made up of the same elements. Even then earth is the only planet among them where life could evolve and exist. We shall now discuss the various factors which made our own planet earth so unique by creating the conditions suitable for the evolution and survival of various life forms which is known as biological revolution. There are three major factors which helped the earth to lead the biological revolution :
(1) The earth is at just the right distance from the sun.
(2) The earth has just the right mass.
(3) The earth has just the right gravitational field.
We shall now discuss all these factors in detail, one by one.
Distance from Sun :
The earth had just the right distance from the sun to make sure that it had the right temperature range for the creation of life. This is because the distance of earth from sun decides its temperature. The earth is at such a distance from the sun that it is neither too hot nor too cold. This factor has helped earth in the creation of life on it. It has now been calculated by scientists that the basic life-support zone exists in a region of space about 65 million kilometres on either side of earth’s orbit. Since Venus is situated on the inner edge and mars is situated on the outer edge of this life-supporting zone, there is no life on Venus and mars.
Mass of Earth :
The earth had just the right mass to make sure that there is an ocean of water on it to support life. That the formation of oceans on earth depended on its mass will become clear from the following discussion. The mass of earth determines the amount of radioactive elements present in it which can release energy to heat the earth. More mass means rapid heating whereas less mass means slow heating. Now, earth had just the right mass so that the heat produced due to radioactivity in it first released the gases like nitrogen, hydrogen and carbon dioxide into the atmosphere, and only after the formation of this protective atmosphere, the water trapped in earth’s hydrated minerals was released as water vapour.
Since an atmosphere of gases existed already, this water vapour was not allowed to escape into the outer space. This water vapour went up, got cooled, condensed, and fell to earth as rain water. This rain water filled the low-lying areas of earth turning them into oceans. And these oceans then acted like a cradle for the primitive life to originate. If, however, the earth had more mass and got heated in such a way so as to expel water before the formation of atmosphere, then this water would have escaped into the outer space and there could be no oceans on this earth. On the other hand, if earth had less mass, then its heating would have been insufficient to expel water from its hydrated minerals,
Gravitational Field :
The mass of earth also decides its gravitational pull. The earth had just the right mass to exert the right gravitational field and this gravitational field helped the earth to hold on to its atmosphere. Without this gravitational field of earth, all the atmospheric gases would have vanished into outer space. Even the rain falls on the earth due to gravitational pull of the earth.
From the above discussion we have learnt that due to its heat content, the primitive earth behaved as an engine. And this earth’s engine separated the primitive earth into three spheres called litho-sphere, atmosphere and hydrosphere (or oceans). These three spheres of earth system then worked together by utilizing the solar energy (sun’s energy) and created the sphere of life called biosphere.