Dr. N.L. Kachhara
Panspermia is the hypothesis that seeds of life are prevalent throughout the universe, and furthermore that life on Earth began by such seeds landing on Earth and propagating them. Panspermia can be said to be either interstellar or interplanetary. There is as yet no compelling evidence to support or contradict it, although the majority view holds that Panspermia especially in its interstellar form is unlikely given the challenges of survival and transport in space. Sir Fred Hoyle and Chandra Wickramsinghe were important proponents of the hypothesis who further contended that life forms continue to enter Earth's atmosphere, and may be responsible for epidemic out breaks, new diseases, and the genetic novelty necessary for macro evolution.
Until a large portion of the galaxy is surveyed for signs of life or contact is made with other civilizations, the Panspermia hypothesis in its fullest meaning will remain difficult to test. There is, however, circumstantial evidence for exogenesis. The Precambrian fossil record indicates that life appeared soon after the Earth was formed. Unless the Earth just happened to be the site of a large number of fortuitous coincidences, this would imply that life appears in several hundred million years when conditions are favourable. Evidence has accumulated that some bacteria are more resistant to extreme conditions than previously recognized, and may be able to survive for very long period of time even in deep space. Narlikar et al. took air samples at 41 km over Hyderabad above the tropopause where mixing from lower atmosphere is unexpected from which rod and coccoid bacteria were isolated. These extremophiles could possibly travel in a dormant state between environments suitable for ongoing life such as planetary surfaces. Another line of evidence comes from research that shows there are many more potential habitats for life than Earth like planets. The Mars exploration Rover missions confirmed the presence of post liquid water on Mars, suggested by river- like formations on the red planet.
No undisputed evidence has ever been published in a mainstream scientific journal to suggest that intelligent alien species have visited the Earth. The majority view in the scientific community seems to be on acceptance that the existence of intelligent life elsewhere in the universe is at least highly probable, due to the sheer number of potential sites where life could take hold. However, the special theory of relativity holds that travel over the vast distances between stars would be limited to the speed of light, and so take such a long time that many scientists think it unlikely that such travel would be practical for life forms as we know them. Over the past century, thousands of people have reported UFO sightings in countries all over world. Some remain unexplained.
There are some objections to Pansphermia and exogenesis. Life requires heavy elements carbon, nitrogen and oxygen to exist at sufficient densities and temperatures for the chemical reactions between them to occur. These conditions are not wide spread in the universe, so this limits the distribution of life as an ongoing process. This, of course, presupposes that any life needs those elements, which the proponents of alternative biochemistries do not consider certain.
