If I consider all the living things on earth, they all are constructed of complex organic molecules where carbon atom plays a central role. But million years ago when the Earth had just condensed out of the gas and space dust, there was no life! How did this transition from a barren land to an overflowing lively world happen? How did the first living thing arise out of the non-living matter existed at that time?
If we see now, we find it a lucky coincidence that our Earth is perfectly suitable for life – moderate temperatures, liquid water, oxygen atmosphere and so on. But million years before, those earlier forms of life that did not well adopted died and thus we are descended from the organisms that did well (this should sound lucky if you are here in the world). About 4 billion years ago, after some time when the Earth had just came into existence, lightning and ultraviolet light from the sun were breaking apart the simple hydrogen-rich molecules of the primitive atmosphere (that’s what Earth was in its early stage), the fragments of which combining into more and more complex molecules until by accident, a molecule arose that was able to make crude copies of itself and that was the early phase of what we call today as DNA. Evolution had been taking place over a billion years slowly and gradually.
The early human grew up in forests. We had been close to nature right from the beginning. We had been around these lovely trees after our race came in to existence. Trees are great and beautiful machines, powered by sunlight, taking in water from the ground and carbon dioxide from the air, converting these materials into food for their use and ours. The plant uses the carbohydrates as an energy source to go about its planty business while we animals, who are ultimately parasites on the plants, steal the carbohydrates so we can go about our business. In the process we exhale carbon dioxide, which the plants then recycle it to make more carbohydrates. What a marvelous example is this of a cooperative arrangement and the entire elegant cycle powered by a star 150 million kilometers away.
At the very heart of life on earth, the proteins that control cell chemistry and the nucleic acids that carry the hereditary instructions are essentially identical in all the plants and the animals. An oak tree and I are made of the same stuff. We have a common organic chemistry (which is responsible for our present) and a common evolutionary heritage (responsible for our past and future). We both use nucleic acids for heredity; we both use proteins as enzymes to control the chemistry of our cells. If we go far enough back, we all share a common ancestor. As a result, our biologists on Earth study only a single kind of biology be it about plants or animals. One could wonder if this is the only form of life in this cosmos. Is this the only voice for thousands of light years? Or is there a cosmic fugue out there? For a moment if I try to be open-minded here considering all the possibilities, If I say that the life music of galaxy can be called coming out from an orchestra, probably we are just familiar with one key note what we could hear on Earth.
(Summarized from COSMOS by Dr. Carl Sagan)