By Robert Deyes
On August 1st, 2008, NASA revealed how its Deep Impact Spacecraft had filmed the moon passing in front of earth from a distance of 31 million miles (Ref 1). The objective of this particular experiment was clear- to see what earth looked like from a distance and to use this result as a means of identifying planets in far off solar systems that might harbor life (Ref 1). Amongst other life-bearing features, the film revealed oceans glinting in the sun light and the infra-red light emissions of plants across the earth's continents. And yet for origin-of-life enthusiasts there remained a crucial question- if basic life forms were indeed found in the distant recesses of our galaxy, what would this really tell us about the inevitability of life's origins on earth?
'Life, Life Everywhere' was the title of a 1996 article in Scientific American that focused on the crucial question of whether the origins of life were truly an inevitable consequence of some fundamental natural tendency in the universe towards great complexity (Ref 2). From our modern stand point, it was really Fred Hoyle that challenged this 'inevitablist' school by proclaiming vehemently that, "the emergence of a living cell from an inanimate chemical soup is about as likely as the assembly of a 747 by a whirlwind passing through a junkyard" (Ref 2). So the modern 'improbabilist' was born, taking on the contrasting inevitabilist view in a head to head intellectual battle. While the inevitabilists used the sudden appearance of the cell almost 3.85 billion years ago (Ref 3) as evidence of life's inevitability, improbabilists such as the late Francis Crick proposed that life was unlikely to have arisen on earth and must have been seeded from outer space (Ref 2). After all if life were truly a rare phenomenon, space transportation networks would have been required to spread it around hospitable planets.
In April of 2001, scientists from the University of Pennsylvania published a series of findings that appeared to strengthen the improbabilist assertions of cosmic origins. Having drilled into crystals that had been obtained from salt deposits deep down below the earth's surface in New Mexico, Russell Vreeland and his colleague William Rosenzweig were able to grow bacterial cultures from these crystals in their own laboratory (Ref 4). These crystals were extraordinary for one simple reason- they appeared to be 250 million years old (Ref 4). Vreeland claimed that if these bacteria had really lasted for this long, there was no reason to believe that they could not just as easily exist on seemingly inhospitable environments such as the Martian permafrost (Ref 4). And yet many researchers were skeptical about the significance of these seemingly ancient survivors of a bygone era. Thomas Lindahl, for example, argued that DNA could not have survived for more than a few thousand years and that as a result these bacteria could not be anything more than a few, more recent contaminants (Ref 4). Svante Paabo from the Max Planck institute for Evolutionary Anthropology had similar reservations. According to Paabo, DNA in a watery environment such as the cell could not have survived more than 100,000 years (Ref 4). The DNA sequences themselves became the focal point for University of Washington Professor David Nickle who argued that the DNA was far too similar to that of modern bacteria. Vreeland dismissed this contention on the premise that modern bacteria are themselves ancient organisms that had escaped their conditions of deep underground isolation (Ref 4). Moreover, Vreeland argued, bacterial spores might have provided an effective barrier against damaging cosmic radiation.
Whatever the outcome of this particular debate, Vreeland's result re-injected energy into the improbabilist camp with its claim that life could have been seeded from outer-space. For proponents of panspermia such as David McKay from the NASA Johnson Space Center, the possibility of finding evidence of similar life forms on the surface of meteorites became an important focus (Ref 5). Cardiff University professor of astronomy Chandra Wickramasinghe likewise believes that life could have been brought to earth on some sort of ubiquitous cosmic dust (Ref 6). The late microbiologist David Wynn-Williams dedicated much of his career to demonstrating how microbes might be able to adapt to "environmental extremes" (Ref 7). For scientists such as myself the case for panspermia remained deeply unsatisfying. After all, rather than explaining the origin of the simplest forms of life panspermists simply pushed it out into the cosmos. The Improbabilist's question on how life arose stood as unanswered as ever.
There have been a number of reports of possible life forms found on meteorites ever since the German geologist Otto Hahn wrote his famous text 'Die Meteorite' in 1880. David McKay and his colleagues for example, published their work on meteorite ALH84001 which collided some 13,000 years ago in the deepest recesses of the Antarctic (Ref 5). The objective of the McKay study was to look for signs of life within the pores of ALH84001 and thereby demonstrate conclusively that life indeed could exist outside of our own planet (Ref 5). It was clear that evidence for the presence of extraterrestrial life forms on ALH84001 would be difficult to demonstrate. For one, the study assumed that such life forms would be similar to those found on earth (Ref 5). Nevertheless the researchers pressed on with their investigations in great anticipation and reported the presence of globular structures around 1 to 250 micrometers in diameter.
McKay and his team also detected long complex organic compounds called polycyclic aromatic hydrocarbons (PAHs) which are of enormous interest to space scientists because of their abundance both in our solar system and the universe (Ref 8). McKay and his team found that PAH concentrations in interior fractures of the meteorite were much higher than any PAH concentrations that had been found on ice sheets on earth (Ref 5). Moreover the limited number of PAHs on the meteorite suggested to McKay and his team that they had arisen through diagenesis- the common breakdown of microorganisms and wildlife. McKay and others therefore concluded that these PAHs could only have come from microorganisms that were already present on the meteorite when it impacted 13,000 years ago (Ref 5).
No sooner had the report on ALH84001 been published, a series of letters appeared in the Science journal concerning the implications of McKay's conclusions. Frank Von Hippel from the Department of Earth and Environmental Sciences at Columbia University, commented that ALH84001 might provide the much-sought-after evidence that life could survive the most extreme of conditions as it hurtled through the cosmic rays and ultraviolet radiation of space (Ref 9). Some scientists today believe that microbes can literally, "hitch a ride" on meteorites drifting in the interstellar void to perhaps colonize planets outside of our solar system (Ref 10). Others such as physicist Harold Morowitz and pathologist Louis de Tolla have expressed their doubt over the significance of the ALH84001 results (Refs 11, 12). Both commented that structures found on ALH84001 which were initially thought of as remnants of bacteria, would have been too small to fulfill the minimal biochemical requirements of a simple cell (Ref 11, 12). Monica Grady, Ian Wright and Colin Pillinger from the Planetary Sciences Research Institute and the Natural History Museum in the UK have questioned the presumed biological origins of carbonates found on ALH84001 (Ref 13).
Even if the nanostructures of ALH84001 do turn out to be primitive forms of life this fact alone would tell us nothing about the inevitability of life in our cosmos (Ref 14, p. 243). The debate is still raging between the improbabilists and inevitabilists with Gustaf Arrhenius, the grandson of panspermist Svante Arrhenius, preferring to remain undecided over the whole issue (Ref 2). And yet for improbabilists and inevitabilists alike, the underlying question of how life arose continues to plague their theoretical meanderings. Physicist Paul Davies had this to say about the shortfalls of panspermia and life's supposedly cosmic origins:
"Some scientists have seized on the panspermia theory in an attempt to evade the problems of biogenesis. If life can propagate between star systems, then only one planet is needed to spawn life, somewhere in the vastness of the cosmos, to account for the existence of life on Earth. I do not share this enthusiasm for evasion. It seems to me that shunting the problem off into outer space does nothing to address the central problem of biogenesis- the problem that has plagued researchers in this discipline for decades- which is that life seems just too good to be true." (Ref 14, pp.242-243)
As Harvard paleontologist Andy Knoll noted, the leap from non-living ingredients to fully-fledged life remains, "an astonishing mystery that we truly do not understand" (Ref 15).
1. Film Shows Earth as Alien World, Scientific Computing, 1st August, 2008,
2. John Horgan (1996), 'Life, Life Everywhere', Scientific American, In Focus, November 25, 1996
3. Martin van Kranendonk spoke on Neil de Grasse Tyson's discussion on the sudden origins of life in a NOVA documentary that aired on PBS on the 28th of September 2004, entitled "Origins: How Life Began"
4. Jonathan Knight (2001), The Immortals, New Scientist, 28th April, 2001, pp.36-39
5. David S McKay et al (1996), Search for Past Life on Mars: Possible Relic of Biogenic Activity in Martian Meteorite ALH84001 Science, Vol 273, pp.924-930
6. See Chandra Wickramasinghe's testimony at the 1981 Arkansas trial on creation which can be found at http://www.panspermia.org/chandra.htm
7. See review on the life of David Wynn-Williams which can be found in The Times (Of London), Wednesday, 27th March, 2002, p.39
8. Max P. Bernstein, Scott A. Sandford and Louis J. Allamandola (1999), Life's Far-Flung Raw Materials, Scientific American, Feature Article, July 1999
9. Frank Von Hippel (1996) Letter In 'Past Life on Mars?' Science, Vol 273, pp.1639-1641
10. Jeff Hecht (2001), Life will find a way, New Scientist, 17th March, 2001, p.4
11. Harold Morowitz (1996), Letter in 'Past Life on Mars?', Science, Vol 273, pp.1639-1641
12. Louis deTolla(1996), Letter in 'Past Life on Mars?', Science Vol 273 pp.1639-1641
13. Monica Grady et al (1996), Opening A Martian Can Of Worms?, Nature, Vol 382 pp.575-576
14. Paul Davies (1999), The Fifth Miracle, The Search for the Origin and The Meaning of Life, Published by Simon and Schuster, New York
15. Andy Knoll spoke on Neil de Grasse Tyson's discussion on the origins of life in a NOVA documentary that aired on PBS on the 28th of September 2004, entitled "Origins: How Life Began"
Copyright (c), 2008, Robert Deyes
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