What we see in the night sky is a tiny part of the infinite universe. With the discovery of the Earth being around the planet to the invention of nuclear weapons, numerous theories have come up now and then as of how did the universe, the Earth, and most importantly how did we come into being?
Origin of Earth
Earth’s origin has always been a controversial affair. Different scientists from time to time gave their own explanations as of how the earth was created.
Nebular Hypothesis – The very first person to give a theory regarding the origin of the earth was a German Philosopher Immanuel Kant. Laplace revised the theory in 1796. According to the hypothesis, a slowly rotating youthful sun was a cloud of various materials which was responsible for the creation of the planets to.
In 1900 Chamberlain and Moulton put forward another theory. It involved a wandering star which approached the sun due to which a cigar shaped extension was formed. It slowly started separating from the solar surface and started revolving around it, giving rise to the planets.
In 1950, two scientists – Otto Schmidt of Russia and Carl Weizascar of Germany – revised the former Nebular Hypothesis. They postulated that the previously formed sun was surrounded by dust and gases like Hydrogen and Helium. Due to movement, there was a collision between the particles which further helped in accretion and formation of the solar system.
The modern theory is the Big Bang Theory or in other words, the theory of an expanding universe. Edwin Hubble came up with it 1920. He theorised that the universe was created 13.7 billion years ago. At that time, it was just a tiny ball with infinite temperature and density. A singularity.
The tiny ball exploded violently, with temperatures dropping at near infinite speeds. A large amount of energy was released – converted into matter. The first few minutes of the Big Bang were very important since at that time the first atom was formed. After that temperature started decreasing rapidly, and galaxy formed, by the accumulation of hydrogen gas (nebula).
Formation of planets was associated with the coming together of the gas particles because of the dust developing around them. There was a high amount of gravitational force between the particles and they were in constant rotational motion which created a centripetal force thereby forming the planets. The gas cloud condensed to form planetesimals (due to cohesion). There was an accretion of the large number of planetesimals to form planets.
It was suggested by Sir George Darwin in 1838 that eventually the earth and the moon were a single body and the moon separated from the earth (now the Pacific Ocean). But this theory of moon’s formation was rejected and later, the theory of giant impact came up.
Evolution of Earth
Initially, the earth was a hot ball of rock surrounded by hydrogen and helium. From 4600 million years ago to present, numerous changes took place due to which we have the earth of today. Because of the high temperature of the earth, constant precipitation took place, which slowly cooled down the earth’s surface and led to the creation of the present-day atmosphere.
Finally, the earth that was formed had a layered structure. This was because of the gradual cooling. The outermost surface cooled faster thereby forming the crust. The innermost still remains in the molten form and has not solidified yet.
Origin of Life
Initial conditions on earth were certainly not suitable enough for life. Too hot, too acidic, and a lot of other inconvenient parameters. Gradually, as the Earth cooled, life had a chance. This is the theory is abiogenesis. Organic matter gradually formed. Early Earth’s atmosphere was formed of methane, ammonia, and water vapour. Due to reduction processes, organic compounds sprung up. From the organic compounds evolved Archaea and Eukaryota, which are also known as the tree of life. So it was likely spontaneous generation that was responsible for the origin of life on earth.