the building blocks of life occurred elsewhere. But the problem lay in finding an explanation as to how they came to Earth in  large  numbers. One explanation could be derived from research undertaken by Luann Becker and Jeffrey Bada of the Scripps Institute of Oceanography in San Diego. Becker and Bada have been examining the Sudbury crater in Central Ontario. This is  the second largest impact crater in the world and measures 60 kilometres by 27 kilometres. Their research has uncovered a large number of buckyballs (football-shaped cages of carbon atoms) among the debris. Together with Robert Poreda of the University of Rochester, Becker and Bada have drawn the conclusion that these carbon molecules were not formed on Earth, but were formed before the solar system emerged and were swept up by a comet which eventually crashed into the Earth forming the Sudbury crater (Pool, 1996).

Critics of panspermia have drawn attention to the problem as to how mi-crobes or elementary living particles could escape from their own planetary system and become attached to comets or other planets such as Earth. In reply it could be argued that it is theoretically possible that microbes in clouds of dust particles could be carried away by the strong repulsive force of radiation pressure from a planet’s home star. This radiation is greater when a star reaches its final red giant stage and could expel dust cloud organisms into space where they would travel until trapped by the gravitational pull of a passing comet, or solar system. In this way life would be regenerated from a dying system.

Hoyle and Wickramasinghe’s theory continues to gain in plausibility. In January 2000, Sandip and Sonati Chakrabarti, at the S.N. Bose National Centre for Basic Science in Calcutta, constructed a computer model to show how chemicals can evolve in a collapsing interstellar cloud, which revealed the possible large-scale production of the DNA base adenine.

Directed Panspermia

Francis Crick (1981) raised more than a few eyebrows in the scientific community when he revised the suggestion that life had been exported from extrater-restrial sources and proposed a theory of Directed Panspermia to account for the origin of life on Earth. Crick speculated that over 4 billion years ago – when the solar system was being formed – there already existed within our galaxy a very advanced civilization. It is likely, he speculated, that they discovered many potentially habitable zones which they seeded with life. The best way to do this would involve sending bacteria – as soon as the planet cooled – by means of automatic space probes. Bacteria would survive the long cold journey through space and could thrive on a young planet without oxygen.

Crick’s speculation could be dismissed as science fiction, but in doing so we would lose valuable insights into the generation of new scientific ideas. It may be instructive to recapitulate the development of Crick’s account of Directed Panspermia.

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Crick (1981: 15) calculated that even with the help of happy accidents, such as the extinction of the dinosaurs, it would take ‘roughly four billion years from soup to man’. This, of course, is based on assumptions about evolution on Earth and Crick acknowledges that there is no way of showing that this could be  the case elsewhere. Crick then considered the estimated age of the universe to be about 10 billion years (opinion now appears to range between 8 and 15 billion). This could mean that intelligent life could have evolved from scratch twice in succession. Given a billion years for the evolution of early plants, life in some parts of the galaxy could have emerged 9 billion years ago, and some 5 billion years ago it could have reached a technological level similar to our own today. This could place them 4 billion years ahead of us if they survived. In any case, it would seem that they might have had time to build a  rocket  containing  some simple life-forms and send it to Earth. With their higher technology they could have manufactured unmanned space probes which explored the nearby stars and, within several hundred years, reported back on the suitability for life in various regions. Suppose, says Crick, they found that life is very rare. Or maybe they never found any at all, or concluded – rightly or wrongly – that they were alone, even though they found places where it could survive and adapt. Possibly, like us, they knew how difficult it is for life to spontaneously emerge. They might have known, also, that in the long run their own civilization was doomed, and very likely thought of exporting life. The distances could have been too great to set up and manage colonies. Perhaps they had tried colonizing nearby planets and, for various reasons, reached an end to colonial expansion. But this still left the possibility of sending simple forms of life to potentially hospitable planets. Men, monkeys and mice might not survive the long journey or the conditions on a host planet, which may lack an oxygenated atmosphere in its early stages. But bacteria are tremendously versatile; they can live in hot springs and  barren deserts, and even survive conditions of intense radiation. In fact, Crick was only speculating about what is now considered a feasible proposal for the ‘greening’ or terraforming of the planet Mars.

Crick then considered rockets travelling at 1/100 speed of light, which is about ten times faster than currently known speeds. They would reach other star systems of 100 light years distance within 10,000 years. Bacteria could survive this time. Moreover, these micro-organisms could be genetically modified to assist survival and adaptation to their new environment. Directed Panspermia overcomes two objections to previous panspermia hypotheses, namely [1] the vulnerability of spores to destruction by solar radiation; and [2] the lack of a plausible natural mechanism for impelling the spore-bearing containers out of the original planet’s gravitational field. An intelligently designed rocket will provide protection for the spores and guarantee their escape from the original planet.

The hypothesis of Directed Panspermia could be dismissed as a piece of speculative nonsense. It is certainly untestable. But it is important to consider some of the philosophical issues raised by Crick, especially if we note processes

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