Purana - The Story of Pralaya

The Puranas describe two types of Pralaya - Khandapralaya in which there is partial destruction and Mahapralaya in which there is total destruction. Normally a Khandapralaya takes place after every Manvantara or the reign of a Manu while a Mahapralaya takes place at the end of a Kalpa or the day of Brahma. In Mahapralaya everything is destroyed, i.e. get back to the source, the unmanifest, and creation begins anew. In a Khandapralaya there is the destruction of many species of animals including human beings, but some survive to begin a new cycle. During the time of Pralaya first there would be a widespread famine that would last for many years as there will be no rain for many years. No plants, corns and herbs will be available and animals will die in hordes. Next there will be a tremendous heatwave from the sevenfold power of the seven rays of the sun that would scorch all surviving animals. The heat will dry up all water and they will accumulate in the form of vapours. Next from the subterranean region Sesha will emit tremendous fumes and flames that will come out and burn everything and Siva's third eye will open and burn the world. Then seven destructive clouds led by Samvartaka will spring up from the vapours accumulated and it will rain continuously for many years until seas are all united into one great mass. Earth will be a vast expanse of water and nothing will survive that.

Note how this vision realistically depicts the scientific conditions of the earth during its creation as well as possibility during the stages when major species like the dinosaurs disappeared from the earth. First earth was a big fireball, extremely hot and then gases formed and then volcanic eruptions were galore. Then rain came and water bodies formed and in the vast mass of water first signs of life appeared in the form of simple carbon molecules who replicated and coalesced to form bigger and more complex organisms. When major species disappeared from the earth owing to large scale destruction, new species appeared after earth being habitable again.