The history of life has two aspects: the origin of life on earth, and the mechanism of gradual changes and adaptations of living organisms through time, known as the evolution of life. Evolution is explained through the theories of Lamarck and Darwin.
1. Origin of the Universe and the Earth
- Origin of life is linked with the origin of earth.
- The Big Bang theory explains the origin of the universe. It proposes that the universe had an explosive beginning (Big Bang) and originated 15 billion years ago.
- The universe comprised stars, clouds of gas and dust which form the galaxies.
- The solar system was probably created when the gaseous clouds started to collapse due to the force of their own gravity, forming atoms and particles. Atoms, dust grains and the gaseous disc aggregated to form clumps and gave rise to planets. This forms the solar system of the milky way galaxy.
- Earth was formed about 4.5 billion years back. Life appeared 500 million years after the formation of earth.