Letter:Bacteria and the beginning of life

Sir: Charles Arthur's article, "A comet full of soup" (29 July), refers to ideas that we ourselves have expounded over many years. The article gives the impression that Mayo Greenberg was the first to suggest that life arose through the introduction of organic material from comets, rather than in a purely earthbound "primordial soup", whereas one of us already considered an extension of the primordial soup to include the entire solar nebula in Frontiers of Astronomy in 1955, long before Professor Greenberg had expressed any opinions on this matter. The evolution of our own ideas on these matters is traced in our most recent book Our Place in the Cosmos (Orion, 1996).

Recent developments in astronomy have shown that light absorption properties of cosmic dust are strikingly similar to those of bacteria and spores - as indeed we have argued for nearly two decades. The organic matter in space resembles the stuff of life, and the problem then is to understand how such material is produced. The choice is whether the material is generated biologically, by means of biological replication in suitable sites such as comets, or whether it is produced non-biologically in a way that somehow mimics the living process. We have always thought that the biological option is preferable to invoking a process which is essentially untestable.

Professor Greenberg is quoted as saying that we are mistaken in considering this particular option because "Bacteria couldn't survive in space. Ultraviolet would destroy them ... the idea of interstellar `spores' is ... nonsensical". Such strongly emotive words surely cannot be justified. Bacterial spores in space are most easily protected from UV radiation because they would inevitably acquire thin coatings of protective carbonaceous material (suntan lotion!).

The humbling lesson of microbiology over the past decade has been to show how exceedingly sturdy bacterial systems really are, and how they can survive under the most extreme conditions imaginable. Some species eg micrococcus radiodurans are known to survive radiation doses equivalent to what would occur in interstellar clouds over millions of years, and of course bacteria in the interiors of comets could survive for indefinite lengths of time.

Our original ideas as described in Lifecloud (1978) relating to the need to import life molecules from space is now adopted pretty well without dissent. But the more powerful and radical concept of life coming in the form of fully fledged bacteria is resisted for reasons that are more to do with sociology than science. Professor Greenberg and other scientists in the field who are clamouring for priority over the weaker of the two options that we discussed in Lifecloud are lagging nearly two decades behind.

Professor Sir FRED HOYLE

Professor N C WICKRAMASINGHE

Cardiff