From Origin of Earth to Origin of Life

1. Evolution is a slow, continuous and irreversible process of change.

2. Origin of Earth: The Big Bang Theory proposes that the universe had an explosive beginning. The universe originated about 20 billion years ago by a big bang (thermonuclear explosion) of a dense entity. About 4.6 billion years ago, our solar system was probably created when the gaseous cloud called Solar Nebula started to collapse under the force of its own gravity, until it became a flattened spinning disc of atoms and particles. Its central region heated up and became a star.

3. Earth is about 4.6 billion years old, and the oldest rocks that have persisted in recognizable form are about 3.8 billion years old. For many years, scientists believed that such ancient rocks did not contain any fossils, but they knew that fossils were simply too small to be seen clearly without an electron microscope.

4. The oldest microfossils discovered so far are that of cyanobacteria that appeared 3.3 to 3.5 billion years ago.

5. Massive limestone deposits called Stromatolites became frequent in the fossil record about 2.8 billion years ago. Produced by cyanobacteria, stromatolites were abundant in virtually all freshwater and marine communities until about 1.6 billion years ago.

6. The fossil records indicate that unicellular protists -the first eukaryotes -appeared about 1.5 billion years ago.

7. Basic unit of evolution is population.

According to recent literature, the first non-cellularforms of life could have originated 3 billion years back. They would have been giant molecules (RNA, protein, polysaccharides etc.) These capsules reproduced their molecules perhaps. The first cellular form of life did not possibly originate till about 2000 million years ago.