Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization
© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm
7.1 Historical Views on the Origin of Life
Speculations on the source of life have been abundant throughout recorded history. The Rig Veda mentions that biology began from the primary elements, and the Atharva Veda suggests that the oceans were the cradle of life. The Bible, with its contradictory accounts of the Creation in Genesis (did man arrive before or after the beasts?), is strictly adhered to by many fundamentalists. Philip Henry Gosse, an eminent 19th century zoologist and Christian, found it a simple task to reconcile the growing mass of paleontological evidence with the Scriptures. God, he declared, created the Earth entirely in accordance with scientific findings. The Lord fabricated geological strata, embedded fossils and the like for the sole purpose of fooling geologists. The apparently extreme age of Earth is only an illusion.
Peculiar ideas abound. Hylozoism, for instance, is the belief that matter and life are one and inseparable. From this viewpoint, life either has no origin and has always existed, or else the question may be deferred to the origin of all matter.
The theory of pyrozoa, to cite another example, was advanced by William Preyer in the last century. Preyer believed that life has existed at all times, even when our planet was still in the molten state. These first fiery living things, the pyrozoa, slowly modified and adapted themselves as the environment cooled and changed, eventually assuming the form in which life presents itself to us today.2218
Most theories on the origin of life have fallen into one of four distinct categories:
1. Life has no origin -- both life and matter have existed forever;
2. Life is the consequence of a supernatural event, intractable and in explicable by the methods of science;
3. Life originated via ordinary chemical evolution in a deterministic fashion -- under similar circumstances, the same general evolutionary patterns would repeat themselves on any world; and
4. Life originated elsewhere by means unknown, and was subsequently transported to Earth (panspermia).
The first two are self-explanatory, and the third closely approximates the leading modern theories. The last deserves a word of explanation.
The Greek philosopher Anaxagoras of Clazomenae (ca. 500-428 B.C.) was possibly the first to suggest that the seeds of life permeated the universe. With the downfall of spontaneous generation millennia later, panspermia enjoyed a brief revival. The theory was sponsored by many 19th-century notables, including Richter, Kelvin, Helmholtz, Arrhenius, and the great Italian chemist Avogadro.
The doctrine of lithopanspermia held that meteorites were the means by which life wandered from planet to planet throughout the cosmos. Lord Kelvin, a central proponent of this view, considered it probable that countless life-bearing "stones" existed in space, perhaps as the result of collisions between inhabited worlds. Hermann von Helmholtz, a German philosopher and a pioneer in physics, believed that the interior of a meteorite would be a safe retreat for interplanetary microbes during the long incandescent journey through thick planetary atmospheres. The presence of hydrocarbons in the carbonaceous chondrites was cited as evidence of the biological activities of the tiny organisms from space.
Modern analyses suggest that microscopic lifeforms embedded in interstellar comets are possible, but unlikely. The accumulated radiation dose from cosmic rays and natural internal radioactivity is "embarrassingly high" over the large transit times involved between worlds.22 Furthermore, it is now known that meteorites are of roughly the same age as the rest of the solar system, and that the organic molecules found in chondrites are reproducible by strictly chemical means.208,2030,2219
The famous Swedish physical chemist and Nobelist Svante Arrhenius was the loudest advocate for the theory of radiopanspermia.2304,2305,2306 He suggested that minute spores might be carried upward through planetary atmospheres by convection, where electrical forces could provide sufficient energy to expel them from the body. The pressure of sunlight would then be enough to propel these cosmozoa to other solar systems. Tramping through space, or riding piggyback on small grains of dust, these legions of microscopic interstellar emissaries thus brought the good news of life to the rest of the Galaxy.
Carl Sagan has done a careful analysis of the problem,20 the details of which will not be repeated here. His conclusion is that radiopanspermia is not a viable theory of the origin of life on Earth. Those microbes ejected from a stellar system by radiation pressure accumulate a dose of x-rays and UV three or four orders of magnitude higher than the maximum lethal irradiation sustain able by even the hardiest terrestrial organisms. Shielding won’t help: Life-forms large enough not to be killed aren’t ejected by radiation pressure because they are too heavy.22
The theory that life arose in the ancient swirling gas and dust clouds of interstellar space and then traversed the cosmos, seeding the Galaxy with life, may be called cosmospermia. Dr. J. Mayo Greenberg at New York State University set up a laboratory experiment a few years ago, using tiny grains of matter the size of space dust and appropriate gases. He found that many compounds of relatively high molecular weight could be formed under the influence of ultraviolet radiation. Greenberg evidently believes that a similar mechanism could lead to the production of grains of a size and composition similar to that of viruses.
Dr. Sagan has disputed such theories, noting that any hypothetical extraterrestrial organism of 10-5 cm -- the size of a rabies virus or the PPLO (the smallest lifeform known) -- would have a replication time on the order of two hundred million years. There could only have been fifty or so generations since the Galaxy first formed, insufficient time for natural selection and evolution to operate.141 It is hard to imagine a smaller yet viable organism; the replication time for a larger microbe would be even longer, permitting still fewer generations.
Accidental panspermia is a class of theory typified by the "Gold Garbage Theory," popularized by Dr. Thomas Gold, a leading astrophysicist at the Center for Radiophysics and Space Research at Cornell University. The Garbage Theory was first announced in a paper read before a Los Angeles meeting of space scientists in late 1958,139 and proposes that Earth may have been visited by an expedition of advanced ETs who carelessly allowed some of their native microbiota (picnic basket litter?) to escape. "While this garbage theory of the origin of life understandably lacks appeal," one xenologist notes wryly, "we should not exclude it altogether."20
A similar idea is the concept of directed panspermia, which suggests that organisms were deliberately transmitted to Earth by intelligent beings on another planet.1283 Advanced civilizations might intentionally seed sterile worlds, either as a prelude to colonization or perhaps simply to perpetuate the heritage of life on the home planet as insurance against catastrophe.
Panspermia does not address the phenomenon of abiogenesis but merely displaces the problem in space and time.* Consequently, panspermia hypotheses aren’t strictly relevant to the ultimate origin of life in the universe but simply explain how any particular world might have come to be inhabited.
* One science fiction story suggests that life on Earth may have arisen from biota left behind by a careless time traveler from our planet’s future.636 If any theory begs the question it is this one!
Last updated on 6 December 2008