THE ORIGIN AND EVOLUTION OF THE EARTH
- Immanuel Kant, a German philosopher, gave this theory.
- In 1796, a mathematician Pierre-Simon Laplace reexamined it.
- According to this hypothesis, the planets were moulded out of a cloud of material associated with a young Sun, which was rotating slowly.
- As per these theories, the sun had a companion.
Revised Nebular Hypothesis
- Revised Nebular Hypothesis was propounded by Carl Weizascar in Germany and Otto Schmidt in Russia.
- They regarded that a solar nebula surrounded the sun and that the nebula comprised of chiefly hydrogen, helium and something called dust.
- The collision of particles and the friction caused a disk-shaped cloud to be formed and then the planets were created via the accretion process.
Big Bang Theory
- Alternatively called the expanding universe hypothesis.
- As per this theory, in the beginning, all matter or substance forming this universe existed at one place as a tiny ball. This tiny ball had an extremely small volume, infinite density and temperature.
- At the Big Bang, this ball blasted fiercely and forcefully and started a substantial process of expansion which continues to this day.
- Now it is accepted that this event took place 13.7 billion years ago.
ORIGIN OF EARTH
Formation of Planets
The following are regarded as the stages in the planets’ development:
- The stars are localised gas lumps inside a nebula.
- A core to the gas cloud as well as a spinning disc of dust and gas are created because of the gravitational force within the lumps.
- After this, the cloud of the gas condenses and the matter over the core is changed into tiny rounded objects.
- These small round objects develop into what are called planetesimals by a cohesion process.
- The smaller objects start forming larger bodies by colliding with one another and they stick together because of gravitational force.
- In the last stage, these large number of small planetesimals aggregate to develop into a smaller number of large bodies called planets.