from scratch in little warm ponds on Earth is outmoded. In fact he maintains that life on Earth began as the result of a form of ‘seeding’ of organic molecules as complex as amino acids. This, he claims, is a conservative interpretation of the evidence. Alfred Vidal-Madjar (1994: 413) also cites recent investigations revealing the presence of numerous amino acids that are not found in living organisms on Earth and states that the existence of complex organic compounds of extraterrestrial origins is well established. As Gribbin points out, among the advantages of the ‘seeding’ hypothesis is the extension of time it allows for the complex origins of life to emerge. Life can pre-date existence of the Earth, as complex chemical processes may have been underway for many million years longer than the Earth.
Molecular clouds which allegedly originate in the spiral arms of the galaxy – where stars are born – are now said to contain several complex chemicals, including biochemically important ones such as amino acids, ammonia and formaldehyde. This might indicate a level of greater chemical complexity than is believed to have existed in the early stages of planetary development. There may well be complex molecules in space ready to rain down and promulgate life in hospitable planets. One possible site is the interstellar medium where precursors such as hydrogen cyanide have been found.
Bioastronomy
The laws of physics and chemistry may apply throughout the universe but biology has been an Earthbound science. The prospect of discerning extra-terrestrial life offers biology its greatest ever challenge. Life has already had an opportunity to spread throughout space: spacecraft have crashed on the Moon and have gone beyond the solar system with a probability that micro-organisms remained aboard. Who knows whether they will survive and adapt?
During the latter half of the twentieth century an entire branch of science has emerged which is based on theories concerning possible forms of ET life. Formerly called ‘exobiology’, but re-named ‘bioastronomy’, it involves the study of evolutionary lines that have not developed on Earth. It has been described as the only sub-field of biology that exists without any secure knowledge of whether it has a subject. It has been compared with theology which is concerned with a subject matter that is beyond understanding, and whose existence is disputed, yet claims, like science, to be concerned with certain truths and the methods for proving them. A statement from the Space Science Board of the USA (1962: 1079) captures the optimism of the exobiology pioneers:
The scientific question at stake in exobiology is the most exciting, challenging and profound issue not only of the century but of the whole naturalistic movement that has characterized the history of Western thought for over three hundred years.
87
SETI scientists now prefer to speak of bioastronomy, emphasizing that there is a subject one can point telescopes at. Bioastronomy operates with the same Darwinian rules as terrestrial biology – mutation, natural selection and speciation – despite possible differences of form. Bioastronomers believe that the evolution of intelligence may accelerate or be restricted by various factors, and that it is selectively advantageous. Given that SETI scientists concentrate upon possible Earth-type planets, there is speculation regarding convergent paths of evolution: for example, eyes have independently evolved on at least forty Earth species, although this is not a necessary feature. However, organs of vision, if they evolve, are expected to respond to roughly similar wavelengths of light to our own.
NASA’s bioastronomy programme seeks to understand the origin, evolution and distribution of life in the universe. Bioastronomers divide on the issue whether life will evolve elsewhere as it has done on Earth. Some, for example, maintain that the genetic code, responsible for the structure and make-up of all living things on Earth, evolved from a precise chemical interaction that would occur in the same conditions anywhere in the universe. According to these terms, extraterrestrial life would be broadly similar to that found on Earth. It should be noted, however, that with only slight variations in a territorial niche there could be massive differences in life-forms. Even within the same territorial niche, such as a swamp, there can be variations in living phenomena from an insect to a hippopotamus. A planet with greater gravity would favour life-forms that crawled flat, like crocodiles, or lived in water or swamps where gravity could be countered by buoyancy. The size of life-forms might not be comparable to ours, and life-spans could well be different.
Many bioastronomers are speculative, and consider possible improvements over human form that an advanced species might have. Their speculations include the prediction of larger craniums to house the larger brains usually associated with highly developed species, and possibly extra limbs to facilitate extra dexterity. Further speculations are drawn from the ‘what-might-have-beens’ of Earth’s biological history. Suppose the dinosaurs had not become extinct some 66 million years ago, but continued to evolve while developing brain capacity and physical dexterity equivalent to Homo sapiens today. With their superior strength they would clearly maintain a position as the dominant species. Is it likely that contact with an ET life-form could be an encounter with the descendants of the dinosaur?
Exotic life-forms
It is frequently asked whether other life-forms on other worlds would be constructed out of the same materials as life on Earth; that is, principally of carbon, hydrogen, oxygen and nitrogen. One imaginative and very different form of life was described in Fred Hoyle’s novel, The Black Cloud, which involved a high form of intelligent life organized in a cloud nourished by light from the stars. The most commonly discussed alternative are life-forms where silicon or
88
Pages: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104