=20

What if life on Earth did not begin on=20 Earth?

The = hypothesis=20 that life on Earth began elsewhere received support from an = unlikely=20 source: the Columbia tragedy

By William Orem
(June 1, 2006)=20

UNLIKELY FINDINGS: Evidence from the = Columbia tragedy may support the panspermia hypothesis."=20 src=3D"http://www.stnews.org/images/060601_shuttle.jpg" = width=3D200=20 border=3D0>

UNLIKELY=20 FINDINGS: Evidence from the Columbia tragedy may = support=20 the panspermia hypothesis.
(Source: NASA/Wikipedia)=20

Judeo-Christian tradition has long maintained that the = dizzying=20 variety of life forms found on our planet are the result of = a=20 special moment of Genesis. From this initial premise, = theologians,=20 philosophers and now modern scientists have branched out, = arguing=20 for a single act of creation on a young Earth, an ongoing = process of=20 molecular evolution begun some four billion years ago with=20 replicating nucleic acids and a multitude of intermediate=20 positions.

What has not been at contention in the majority of these = debates=20 has been the premise itself: that life on Earth began on = Earth.

This is precisely a point that needs to be considered, = say=20 contemporary advocates of a hypothesis known as = =93panspermia.=94 In its=20 broadest iteration, panspermia is the proposal that life = exists=20 throughout the cosmos. As simple speculation, it has a = pedigree=20 dating as far back as 500 B.C. with the Greek philosopher = Anaxagoras=20 and makes connections with such luminaries as Giordano = Bruno, the=20 ex-Dominican astronomer put to death by the Inquisition = partly for=20 suggesting that the sky may be full of populated worlds.

One need not posit highly evolved forms, however, to = subscribe to=20 the panspermia hypothesis. Indeed, scientists who take = panspermia=20 seriously today are more concerned with a humbler expression = of=20 life: bacteria.

=93As a group, microorganisms are probably the hardiest = of any life=20 forms on Earth,=94 said Robert McLean, a biologist at Texas = State=20 University-San Marcos, who has collaborated with NASA to = have=20 microbiology experiments performed on the space shuttle. He = said his=20 sense of the fledgling science of astrobiology is that = =93the vast=20 majority of it is going toward microorganisms.=94

McLean is interested in biofilm formation. In particular = he=20 wanted to know how planktonic and surface-adhering bacterial = populations would interact in microgravity conditions. This=20 information has implications for the future of space travel, = in=20 which the filtration of water will be critical. In a paper = published=20 in the January edition of Icarus, the International Journal of Solar System=20 Studies, McLean describes how he selected three = strains =97=20 C. violaceum, P. aeruginoa and E.coli = =97=20 to ride on the space shuttle Columbia in 2003.

=93I think there were 70 to 80 experiments total on the = flight,=94=20 McLean said. =93The Columbia was slanted more toward = scientific work.=20 That was its primary responsibility.=94

On the morning of Feb. 1, 2003, McLean received the = news=20 that broke the nation=92s heart. Columbia had disintegrated = on=20 re-entry, its left wing seal damaged by the now-infamous = dislodged=20 foam. All hands, with their complement of scientific data, = were=20 lost.

Exogenesis hypothesis

Under the general rubric of panspermia lies exogenesis, a = more=20 modest, and perhaps more testable, hypothesis. In its = simplest form,=20 exogenesis is the proposition that life did not begin on = Earth but=20 elsewhere in the stellar region.

One likely candidate would be neighboring Mars, where = oceans are=20 now believed to have existed as recently as several million = years=20 ago. At some point, basic, self-replicating organisms were = then=20 transferred to this planet, explaining the surprisingly = small window=20 between when the geological record dates Earth=92s formation = and when=20 the Precambrian fossil record dates the first appearance of = life.=20

The mechanism by which that transfer of microbes could = take place=20 is meteorites. A collision of a large enough meteorite = impactor with=20 a planetary surface sends up clouds of debris. Retained by = the=20 gravitational field, the ejecta may rain back down or stay = aloft to=20 form rings or moons. At escape velocity, however, = nonvaporized=20 chunks sail away, bound for empty space. In rare instances, = they may=20 eventually come within the gravitational fields of other = planets or=20 moons. Perhaps, as exogenesis suggests, such newly born = asteroids=20 could be bearing travelers.

A couple of days after the Columbia disaster, McLean got = a call.=20

=93One of the people who had an experiment [on Columbia] = happened=20 to get on The New York Times Web site and saw a = picture of=20 some shuttle debris that looked like our payload,=94 he = said. A=20 long-shot idea struck him. Why not test the apparatus for=20 bacteria?

=93There was some liquid that survived in the payload. I = pulled=20 that out and tried to culture stuff from that and also = flushed=20 various sample cells with sterile medium,=94 McLean said. = All three of=20 the bacterial strains he had sent aloft had been wiped out = by=20 Columbia=92s re-entry, during which temperatures peaked at = more than=20 175=B0 C. But after a week or so he noticed something = peculiar in the=20 incubator.

=93In one of the cells that I flushed I eventually found = a very=20 slow-growing organism,=94 he said.

The unexpected survivor was a new bacterial strain known = as=20 Microbispora. While not common, it is by no means=20 extraterrestrial. Microbispora is found in the = Earth=92s=20 soil.

=93The scientific weakness of this is we don=92t = absolutely know=20 where it came from,=94 McLean said. =93But I did do controls = when I=20 collected the samples to make sure I wasn=92t introducing = anything on=20 the site. Those were totally clean. None of the solutions I = took=20 down to Florida were contaminated at all, so I was not = introducing=20 anything.=94

The remaining option, which McLean calls his =93best = guess,=94 is=20 that the Microbispora infiltration occurred before = liftoff.=20 If so, the Columbia crash inadvertently demonstrated the = feasibility=20 of a claim that exogenesis critics and panspermia detractors = in=20 general have found implausible. It showed that some bacteria = can=20 survive the extreme stresses that would be involved in = meteorite=20 entry and impact.

Macroscopic survival

McLean was not the only researcher to be surprised. NASA=20 astrobiologist Catharine Conley works at NASA=92s Ames Research Center in Moffett = Field,=20 Calif. She had sent up a live population of nematodes with = Columbia.=20 Nematodes are a species of worm, each roughly the size of = the period=20 at the end of this sentence. Conley was using them to = conduct a=20 study on bone density disturbances that occur in = microgravity, again=20 with a view toward reducing the risk associated with = long-term space=20 assignments.

When Columbia broke apart, Conley=92s six canisters of = worms were=20 scattered in midair and subjected individually to the = re-entry burn=20 and impact force. Five canisters were eventually recovered. = All five=20 still had live populations inside.

=93Certainly the recovery of vital organisms has = completely changed=20 my opinion of what we might expect to find in the solar = system,=94=20 Conley said. She said her thinking about panspermia has been = affected by her finding, and the thesis now seems more=20 compelling.

=93There has been life on Earth for three or = three-and-a-half=20 billion years,=94 Conley said. =93There have certainly been = a large=20 number of big things that have hit the Earth and blasted = rocks off=20 the Earth in that three-plus billion years.=94

=93The more I think about it now, it seems the more = likely that=20 there have been so many rocks with live organisms [in them] = when=20 they left the Earth floating around the solar system that it = would=20 be surprising to me if there weren=92t living = organisms in=20 places that were hospitable to life,=94 she said.

Indeed, a massive computer modeling study just completed = at the=20 University of British Columbia and presented in March at the = Lunar=20 and Planetary Science Conference in Texas has made it = apparent just=20 how far-ranging these travels may be. In it, a research team = simulated a massive Earth strike on the order of the = impactor that=20 is believed to have formed the Chicxulub crater 65 million = years=20 ago. Their model tracked the debris paths of millions of = ejected=20 fragments and found that potentially life-sustaining sites = as far a=20 way as Europa and Titan (moons of Jupiter and Saturn, = respectively)=20 were eventually hit.

Even some organisms as large as nematodes would be able = to=20 survive such an abrupt ejection into space, Conley said. =

=93The acceleration forces to get to escape velocity for = a=20 meteorite turn out to be not that high,=94 Conley said. = =93If it=92s a big=20 impactor, it will take a long time to penetrate. It=92s more = the mass=20 transfer that=92s actually going to be forcing the smaller = rocks off=20 the planet.=94 And nematodes routinely survive experimental = force=20 conditions of 2,000 Gs or higher. The hard part, she said, = is=20 surviving space =97 the university model predicted a transit = time of=20 millions of years for the Jovian moons, well beyond the = conceivable=20 survival range of even frozen nematodes =97 and surviving = the new=20 environment when it arrives. In that respect, she said=20 microorganisms are more plausible candidates.

=93What you really want is something that can make its = own food,=94=20 Conley said. =93In that case, you=92re looking for something = like a=20 cyanobacteria that make food from light, or one of these = hydrogen=20 sulfide metabolizers that=92s able to get food from rocks. = Or you want=20 something like a lichen, that can both make food from light = and also=20 fix nitrogen.=94

Such an organism might be able to survive the long haul = between=20 worlds and set up shop in a variety of locations. =93If I = were looking=20 for life on another planet, I would go looking for a = lichen,=94 Conley=20 said.

Natural carriers

Max Wallis, Honorary Research Fellow at the = Cardiff=20 Centre for Astrobiology in Wales, has a different = mechanism for=20 long-distance transport in mind. That mechanism is a = comet.

=93Asteroids are pretty dead,=94 he said. He added, = however, that=20 microorganisms are already known to survive in the extreme=20 conditions of the poles. =93Comets have the water and = carbon, and it=92s=20 very accessible. Certainly as an environment for living = organisms=20 they=92re very much like the Antarctic.=94

In an article published in Nature in 1980, = Wallis showed=20 that, despite the popular image of comets as dirty = snowballs, some=20 may house liquid cores. Six years later, as a member of the = European=20 team that sent the Giotto probe to study Halley=92s comet, = Wallis=20 recognized that the structured surface and gas jets revealed = a more=20 complex comet structure than had previously been assumed. He = said he=20 suspects some versions of that complexity could operate like = natural=20 traveling containers. And because of the gravitational = perturbations=20 of Jupiter, comets in the Kuiper belt are, on occasion, = swung out of=20 the solar system entirely.

=93I think comets can form an environment in their = interior in=20 which elementary life can replicate, survive and travel in a = sheltered environment to another stellar system,=94 Wallis = said.

The =93bombardment periods=94 of planetary formation = would still play=20 a critical role. In this model, a good-sized impactor of the = type=20 that were 100 times more frequent in the young solar system = would=20 send a population of microorganisms into space, where some = would=20 eventually be collected by passing comets. The collection = process=20 would be simply mechanical, akin to the way your hair = collects=20 airborne particles as you walk through a room full of = smokers.

=93It=92s basically only the elementary life form =97 the = DNA =97 but=20 that=92s the difficulty in starting life,=94 Wallis said. = =93Once you=92re=20 seeded with life going by in a comet, it would proceed just = the way=20 life has evolved on the Earth.=94

Wallis said that the natural tendency of comets to begin=20 outgassing in the proximity of stars may serve to litter the = orbital=20 path with organic material that then can rain down on = whatever=20 environments are nearby. This type of seeding =97 not just = from planet=20 to planet but from star to star =97 would be true = panspermia.

=93There is a growing body of evidence to support the = idea that=20 life did not originate on the Earth,=94 said Chandra = Wickramasinghe,=20 director of the Cardiff Centre and a major proponent of the=20 panspermia hypothesis.

=93The Earth just happened to be one of innumerable = planets that=20 came to be drenched with these cosmic genes, and evolution = proceeded=20 to piece the genes together as time progressed, subject, of = course,=20 to the criterion that the fittest assemblages are always the = most=20 likely to survive,=94 he said.

At his earthbound lab in Texas, however, McLean urges=20 caution.

=93I=92d like to believe that it=92s true,=94 he said = when considering=20 the possibility of extraterrestrial life of any sort. =93But = I=92m=20 mindful of a saying by Carl Sagan that extraordinary claims = require=20 extraordinary proof. What we=92re reporting is just a really = small=20 piece of the puzzle.=94

William Orem is science editor at Science & = Theology=20 News.

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