Crick’s Joke

Chapter 6G

Crick’s Joke

I was unable to secure permission from the Journal of Cosmology to publish in this blog the 24 commentaries on Richard Hoover’s claim to found cyanobacteria in several meteorites. The gentleman who replied did, however, invite readers of the blog to take a look at the journal. These are the references. The online version is free.

Journal of Cosmology, 2011, Vol 13,
JournalofCosmology.com March, 2011

I should add that the Journal of Cosmology has devoted several issues to panspermia and related topics. I will have to take a look and may perhaps return to this subject in a future posting.

In the meantime, however, I would like to remark, almost in passing, why the whole panspermia movement seems so perplexing to me. I will begin by expressing a nagging doubt about Hoover’s Cyanobacteria claim. From what I could tell, although as I said I will have to read more, Hoover’s claim seems to be based on the physical similarity between the structures he found in meteorites and Cyanobacteria in our planet. The “alien” pedigree is established by the fact that such structures exhibit only 8 of the 22 amino acids we would expect in terrestrial life. It seems to me, then, that even if those structures were indeed fossils, it is a long stretch to classify them as Cyanobacteria. Clearly, they cannot be Cyanobacteria: they don’t have the same proteins, for they don’t have the same amino acids, thus they cannot be the same kind of beast. Think of it another way: they must have radically different proteins, therefore, since genes code for proteins, they must have radically different genomes. Perhaps the classification is given because those structures, when alive, if they were ever alive, also engaged in oxygenic photosynthesis. But I do not know how that could be established from physical similarity.

Now, most defenders of panspermia promote the idea that terrestrial life did not originate on Earth but came from elsewhere. One wonders what kind of evidence they could have for such a claim. It is normally based on two assumptions:

(1) That life could have survived journeys of millions of years before landing on our planet;

(2) That life could not have started on Earth.

The first assumption is bolstered now by Hoover’s evidence for Cyanobacteria. But as I pointed out in my previous posting, Hoover’s findings do not support the notion that terrestrial life came from somewhere else, since presumably they established that those structures are not relatives of terrestrial life forms at all (only 8 amino acids in common, etc.).

The second assumption is rather astonishing. We really do not know how life begins. So how can these people argue that life could not have begun here?

They say that there was no enough time for life to evolve here from organic compounds, that the conditions were not right, and so on. But their reasoning seems very faulty to me. I will try to lay out my objections with some care in my next posting, and perhaps some readers who disagree with me can spot faults with my own reasoning and thus improve my understanding.

I would like to add at this point, though, that some of the more specific claims made by the advocates of panspermia make them lose scientific credibility. I will merely mention a couple that I found in a side article by Lana Tao in issue of the Journal of Cosmology that began this detour a couple of postings back. I will point out next time why they are not scientifically credible.

C. Wickramasinghe: "What we have developed and proposed in this text is a cosmic theory of evolution which completely overturns Darwinism." This appears in a section titled THE DEATH OF DARWINISM, no less.

R. Joseph: “Evolution is not random but is instead the replication of creatures which long ago lived on other planets."

R. Joseph: "Just as apple seeds contain the genetic instructions for the growth of apple trees, these genetic seeds of life contained the DNA-instructions for the Tree of Life, and the metamorphosis of all life, including woman and man: the replication of creatures which long ago lived on other planets."

I will close by remembering Francis Crick funny account of why we will never be able to figure out how life began. Life came to Earth from another world. In that world, scientists developed a synthetic form of life that could withstand the long journey through space. But such life could have never arisen naturally. So by studying natural phenomena, we will never get a clue, for the conditions necessary to bring such life into existence do not naturally exist.

And Gunther Stent quipped that if Francis Crick, the greatest biologist of the 20^th Century had not been able to discover how life began, no one could.

But on the shoulders of giants….

More on Meteorite Bacteria Fossils

Chapter 6f

More on Meteorite Bacteria Fossils

Some readers have expressed great interest in the controversy surrounding Richard Hoover’s claim to have found fossils of cyanobacteria in several meteorites. I have asked permission from the Journal of Cosmology, the online journal that published Hoover’s paper, to reprint the 24 commentaries on Hoover’s alleged discovery. Once I hear from the journal, I will let you know. I said “alleged” two sentences ago because I do not have the technical expertise to critique Hoover’s analysis. I could mention, however, that of the 24 commentaries, only about 8 are by people who do seem to be technically qualified to pass judgment on the quality of Hoover’s work. The others, which include pieces coming from Ph.D.s in many fields, mostly deal with what they take to be the implications of Hoover’s work. Several come from advocates of the panspermia hypothesis, i.e. that life is everywhere and spreads by hitching rides in meteorites, asteroids, comets, etc. Those advocates are also proponents of exogenesis, i.e. the view that Earth life did not originate on Earth but came from elsewhere. Those people believe that Hoover’s work confirms their views.

Of the commentators who actually take up the technical details of Hoover’s paper, about four give him a clean bill of health, mostly on the question of whether his findings could have been the result of contamination of the meteorites by Earth life, although some of them are also struck by the great physical resemblance between the structures he found and cyanobacteria. The reasons for concluding that there was no contamination were (1) lower levels of nitrogen than normally exhibited by modern bacteria, and (2) the presence of only 8 amino acids instead of the 22 employed by living things in this planet. The other four were rather skeptical about his experimental methods and his reasoning, even when expressing interest in his work.

A more definitive assessment would require the kind of peer review normally reserved for results of the upmost importance, a review that would include the experimental work proposed by some of the skeptical commentators. Unfortunately it seems that the major journals and NASA have grown gun shy after the bruising battles concerning the Martian meteorite I have discussed in previous blogs.

Perhaps in my next posting I will be able to include the 24 commentaries. Otherwise I will return to my regular line of thought derived from my manuscript in progress, The Dimming of Starlight. Today, however, I will bring up a couple of comments relevant to the panspermia and exogenesis hypotheses.

One of the commentators though that the meteorites in question were likely Martian. Another though that they could be from the Earth itself: they were thrown into space, and finally they came back. Unless this possibility is excluded, Hoover’s findings would not help the panspermia hypothesis. Now, it seems to me that if Hoover’s structures are indeed extraterrestrial fossils, then this extraordinary finding would support the view that life may be common in the universe. It does not support the exogenesis hypothesis all that much, for, after all, Hoover would have only found fossils, dead things, not living bacteria that survived the long journey through space to Earth (or even bacteria that made it alive to Earth and then died here). Dead is dead. Maybe live extraterrestrial bacteria could make it to Earth and survive, but we cannot infer that from the fact that dead ones made it. If they are indeed bacterial fossils to begin with.

Second, the confirmation of Hoover’s structures as fossils may actually seem to go against the exogenesis hypothesis, for the very strong reason already given to show that they are not the result of contamination, namely that they have only 8 amino acids instead of the earthlings’ 22 customary amino acids. That is, they are radically different from Earth life, even if they have enough similarity to call them life. But if they are radically different from Earth life, we have no evidence that life on Earth has an extraterrestrial origin.

Sometimes, I should mention, the words “panspermia” and “exogenesis” are used as synonyms. That is, panspermia is the flag around which the proponents of the extra-terrestrial origin of life on Earth gather. One of the commentators, the former Appollo 17 astronaut and U.S. senator, Harrison H. Schmitt, wondered why these people are adamant that life could not have evolved independently on Earth. Indeed I wonder too. But more on this next time.

A NEW CONTROVERSY

A NEW CONTROVERSY

I have run across a new controversy concerning fossils from outer space, this time about structures that resemble Cyanobacteria. These structures were found in a meteorite by a Richard Hoover, a NASA scientist. His paper was published by the Journal of Cosmology, an online journal. The official NASA word has been negative, apparently, and the same can be said for the opinion of the scientific elite that has gotten wind of this paper. I am very skeptical of some of the claims that the paper’s supporters have made, but I thought that many of my readers might want to take a look for themselves. I am enclosing two items below. One is an open letter to the editors of Science and Nature, the top two general science journals in the world, by the editors of the Journal of Cosmology. The other is a synopsis of Hoover’s presumed discovery. By going to the journal’s website you may also view several commentaries by people with PhD’s in science, some sensible and some not. The materials can also be found in the newsletter

Journal of Cosmology, 2011, Vol 13,
JournalofCosmology.com March, 2011

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Fossils of Cyanobacteria in CI1 Carbonaceous Meteorites
Richard B. Hoover, Ph.D. NASA/Marshall Space Flight Center

Synopsis

Richard Hoover has discovered evidence of microfossils similar to Cyanobacteria, in freshly fractured slices of the interior surfaces of the Alais, Ivuna, and Orgueil CI1 carbonaceous meteorites. Based on Field Emission Scanning Electron Microscopy (FESEM) and other measures, Richard Hoover has concluded they are indigenous to these meteors and are similar to trichomic cyanobacteria and other trichomic prokaryotes such as filamentous sulfur bacteria. He concludes these fossilized bacteria are not Earthly contaminants but are the fossilized remains of living organisms which lived in the parent bodies of these meteors, e.g. comets, moons, and other astral bodies. Coupled with a wealth of date published elsewhere and in previous editions of the Journal of Cosmology, and as presented in the edited text, "The Biological Big Bang", the implications are that life is everywhere, and that life on Earth may have come from other planets.

Members of the Scientific community were invited to analyze the results and to write critical commentaries or to speculate about the implications. With one exception as it was off topic, all commentaries received were published between March 7 through March 10, 2011. By far, most of the commentaries were positive and supportive of the evidence.

Open Letter to the Editors of Science & Nature

The Journal of Cosmology Proposes a Scientific Commission,
Established Co-Jointly with Science and Nature,
To Investigate & Confirm the Validity of the Hoover Paper

March 11, 2011

Dear Dr. Bruce Alberts and Dr. Philip Campbell:

In 1584, Giordano Bruno published "Of Infinity, the Universe, and the World" and wrote: "There are innumerable suns and an infinite number of planets which circle around their suns as our seven planets circle around our Sun." According to Bruno, we are unable to see these planets and suns "because of their great distance or small mass." On February 19, 1600 Bruno was tortured and burned at the stake by the Inquisition for publishing these claims which contradicted established "scientific" dogma.

The publication of Richard Hoover's paradigm shattering discovery of microfossils within carbonaceous meteorites, unleashed an ugly storm of violent, histrionic invective not seen since the Middle Ages when they burned scientists for making discoveries that threatened the established order. Charlatans and quacks quickly emerged, and the media unabashedly published their ravings, recklessly casting delusional filth upon the reputations of the Journal of Cosmology and its editorial board, and the hundreds of esteemed scientists whose peer reviewed work we have published; a roster which includes two Senior Scientists Science Directorates at NASA, over 30 top NASA scientists, and four astronauts.

How can science advance if the media and NASA administrators promote frothing-at the-mouth-attacks on legitimate scientists and scientific periodicals who dare to publish new discoveries or new ideas? Skepticism is natural. Doubt is healthy. But science cannot progress under a cloud of intimidation and fear.

The Journal of Cosmology (JOC) has reviewed its editorial policies and peer review procedures and determined they are sound. The media has been provided a sample list, the names of nearly 100 top scientists who have served as referees in the past; a veritable "who's who" of the top experts in the world have reviewed papers for JOC.

Hoover's paper was received in November and was repeatedly peer reviewed. After months of careful analysis, it was published on March 5 of 2011. Of the 24 commentaries received, almost all have been supportive of the findings. The results are valid. We have been provided with no evidence they are not.

The implications of Richard Hoover's discoveries are profound. However, given the slanders and paranoid ravings designed to crush all rational discussion of these findings, naturally the public, the media, and the scientific community would be skeptical. They deserve to know with absolute certainty if these findings can withstand the scientific scrutiny of esteemed experts and if his results should be accepted or dismissed.

How can this issue be successfully resolved? Who can the public trust? Science magazine which published the "arsenic-life" study which proved to be untrue? NASA's chief scientist who backed the bogus "arsenic" paper, and has made a number of grossly inaccurate and untruthful remarks about the Hoover issue? The Journal of Cosmology whose reputation has been besmirched by reckless slanders? Nature magazine which has rejected Nobel prize winning research?

Given the ugly climate which now prevails, the validity of the Hoover paper must be resolved as a cooperative effort, through an unprecedented collaborative peer review, monitored and mediated by the Journal of Cosmology and its critics and competitors (Science and Nature), thus guaranteeing a balanced approach and so all points of view are represented. Therefore, the Journal of Cosmology proposes that:

1) JOC, Nature, and Science each appoint an expert-judge who has a background in astrobiology.

2) These 3 expert-judges will appoint and unanimously agree on a panel of 12 esteemed experts who will be guaranteed anonymity if they desire.

3) This expert panel of 12 will have 30 days to review the Hoover paper, ask for supplementary material, and to question Richard Hoover and to call upon the expertise of additional experts, if they so choose. Each of these experts will issue their reports to the 3 expert-judges.

4) The 3 expert-judges will issue their own report(s) summarizing these findings, and issue a verdict on or their opinion of the validity of Hoover's paper as based on the reports issued by the 12 expert panel.

5) Science, Nature, and JOC, will publish the reports of the 12 member expert-jury, and the expert-judges.

6) If the weight of opinion is that Hoover's findings are not valid, the Journal of Cosmology will withdraw the paper.

7) If Hoover's findings are validated, we ask not for a apology, but congratulations.

We believe our proposal is scientifically sound and eminently reasonable. We are completely open to working out the fine details with the editorial boards of Science and Nature

If Science and Nature decline, then any refusal to cooperate, no matter what the excuse, should be seen as a vindication for the Journal of Cosmology and the Hoover paper and an acknowledgment that the editorial policies of the Journal of Cosmology are beyond reproach. The very fact that we have made this proposal, coupled with all our previous efforts to open this issue to scientific discussion and debate, is, itself, testament to the integrity of JOC whose mission has always been to promote and advance science.

Sincerely,
Rudy Schild, Ph.D.
Center for Astrophysics, Harvard-Smithsonian
Editor-in-Chief
Journal of Cosmology

The Serendipity of Astrobiology

Chapter 6E

The Serendipity of Astrobiology

Two remarkable developments in biology are worth mentioning in connection with the serendipity of astrobiology. Let us remember that a key objection to the possibility of Martian fossils in meteorite AL84001 was that the worm-like features could not be bacteria because they were one hundred times smaller than real (terrestrial) bacteria. The controversy, however, spurred interest in the possibility that the Earth itself may contain bacteria that small. The interest increased when it was realized that the methods for looking for bacteria would not have detected such terrestrial “nano-bacteria” even if they existed. Lo and behold: biologists soon claimed to have found many such varieties of bacteria, even smaller than the presumed Martian bugs, right here on our own planet! This discovery, however, seems to have been short lived. More recent investigations revealed that some candidates to the title of nanobacteria are non-living mineral structures, e.g. calcium carbonate crystals, that do mimic bacteria in some respects and even reproduce.[1] Although not as exciting perhaps, this finding is nevertheless quite interesting in its own right. Moreover, it has some practical importance, since those nano structures are apparently in the formation of kidney and other stones.

This serendipitous result of astrobiology, as valuable as it has been in giving us a new understanding of life on Earth, may pale in comparison with the creation in the laboratory of life forms that incorporate a 21^st amino acid and others with non-standard DNA codes![2]

It is clear that much needs to be done in this field, and that space science is particularly well poised to nourish its advance. At the same time we should beware of placing unfair demands upon the field, particularly where it concerns the search for the origins of life. We should beware especially of the carefree use of probabilities in trying to settle this important issue. The most notorious is the estimate of the probability that all the constituent atoms of a cell may come together to form the cell. Even for a strand of DNA the probability would be extremely low. And so it would be for any complex arrangement of matter, as long as we assume that it started from scratch. As Fred Hoyle put it, what is the probability that a Boing 747 will arise spontaneously from a tornado-swept junkyard? Of course the probability is nil. But cells are not formed from scratch. Some elements combine together more easily than others, and if they are abundant then we will find many of their compounds. Such is the case with carbon and hydrogen. Once those compounds are formed, more complex compounds can form using them, and so on. The rising complexity of molecules can give rise to very complex molecules indeed -- and then the very long process of organic evolution can begin.

Robert Shapiro, a critic of the field, tries to impose two requirements that deserve special comment. He claims that the thesis that the origin of life was an accident is not scientific. Apparently he feels that a truly scientific approach would explain why life was inevitable, given the Earth’s early environment. And he also objects to laboratory simulations of hypothetical early terrestrial environments in which the experimenters manipulate the environment to determine whether certain complex molecules can be produced from certain others. He wants the experiments left alone, to see whether the molecule so produced is capable of evolving on its own (otherwise we are not really dealing with organic evolution, I presume). His suggestion is that much of the work in the field fails to meet these two requirements and he concludes that the field is in disarray.[3]

The first thesis is rather strange coming from a biologist. If organic evolution is evolution at all, it is subject to the vagaries of natural history. The evolution of mammals, for example, may have well depended on extraordinary accidents (such as the Alvarez asteroid, which made available to our ancestors the niches previously ruled by dinosaurs).

It seems that Shapiro is unhappy because the search for the origin of life does not demand the sense of inevitability that we expect from physics. But that is one of the differences between physics and historical sciences like geology or biology. But even if we wish to use physics as a model, it seems that either chaos theory or Prigogine's dissipative structures would serve us better. A very small change in initial conditions may lead to radically different outcomes. A tiny amount of a catalyst can produce an oscillating reaction (say where the color of the solution keeps changing from red to blue). At the time of the Cambrian Revolution (about 650 million years ago) there was a great explosion in the forms of life that began to populate the planet. An observer could not have predicted then that human beings were sure to come along millions of years hence, unless he had knowledge of all the accidents that would take place in the ensuing years, and of all the ways in which complex environmental relations were going to change. Nevertheless, this particular outcome of evolution (humans) is an accident, and so is any other particular outcome. If life is the outcome of organic evolution, life itself could be said to be an accident too.

A compromise position may be defended. We need claim neither that life (as we know it) is an accident, nor that such life was inevitable. For example, we may hope for an explanation of origins that makes it look as if some accident of this sort (life) was likely to happen (e.g., a self-reproducing molecule that can protect itself from most typical, short range, environmental dangers, even though its genetic code is very different from ours).

As for Shapiro's second requirement, it seems to me that we should want to create in the laboratory a molecule that can reproduce in the sorts of environments that we think may have existed long ago. It would be unreasonable to demand that such a molecule should reproduce in any environment that might develop if we leave the apparatus unattended. We must remember that most species that ever lived are now extinct. As the environment changed, only those organisms to which the change was not unfavorable were able to leave progeny. Thus, by a similar reasoning, a molecule may be of the right sort and still fail to reproduce under the conditions required by Shapiro instead of conditions similar to those that an evolving Earth made available to its complex organic molecules.

In its own ways, astrobiology thus illustrates how space science preserves the dynamic character of science in general. Its vigorous pursuit would inevitably lead to the profound transformation of our views of the living world. And since those views are linked to our understanding of the global environment, the resulting theoretical adjustment would be of great magnitude — and so eventually would be the change in the way we may interact with the universe. The justification of astrobiology is, then, ultimately much like that of the other space sciences, and in line with the general philosophical position of this essay, whether or not we ever find a single extraterrestrial specimen!

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[1] Martel, Jan, and Ding-E Young, John. “Purported nanobacteria in human blood as calcium carbonate nanoparticles.” Proceedings of the National Academy of Sciences. April 8, 2008. vol. 105, no. 14, 5549-5554.

[2] See, for example, R. F. Service, “Researchers Create First Autonomous Synthetic Life Form,” Science, Vol. 299, 31 January, 2003, p. 640.

[3] R. Shapiro, Origins: A Skeptic’s Guide to the Creation of Life on Earth, Bantam Books, 1987.

The Value of Astrobiology with or without Specimens

Chapter 6D

The Value of Astrobiology with or without Specimens

The lack of extraterrestrial specimens is an objection to the pursuit of astrobiology only if we accept a narrow definition of the field. Astrobiology goes beyond the search for extraterrestrial life: It is largely the application of space science and technology to understand how life may originate and evolve anywhere in the cosmos. As a practical matter, astrobiology often devotes itself to investigating how life originated and evolved on this planet. Astrobiology tries to determine, for example, what the Earth was like 3.5 - 4.5 billion years ago — what was the ultraviolet flux? What were the volcanic and other tectonic activity? How much molecular oxygen was in the atmosphere? And how much ozone? How much carbon, hydrogen, and nitrogen were "recycled" through the Earth's crust and how much were brought to the Earth by asteroids and comets? To decide these issues we must go away from the Earth to study the older surfaces of the Moon and Mars, the presumably still primordial atmosphere of Titan, and the largely untouched chemistry of comets.[1] Astrobiology is thus inseparable from comparative planetology. (Figure 3).

This connection is all the more evident when we remember that to understand the nature of an environment well we need to understand its origin and evolution. In the global environment of the Earth life has played a crucial part (e.g., in the density, temperature, and composition of the atmosphere, cf. Ch. 4). How life originated is thus a question of great importance if we are to understand how our global environment came to be as it is. At the same time, we cannot begin to settle that question without making some critical determinations about how the planet was formed, how its atmosphere was created, how much energy it received from the sun in its early evolution, and in general all those questions that form integral part of comparative planetology.

In trying to answer the question of the origin of life, however, there are great difficulties of substance and of method. For example, some investigators would not be satisfied with an answer unless it demonstrated that life was somehow inevitable or at least very likely. They would require that we specify the early conditions in the planet (e.g., a reducing atmosphere and later a primordial soup of organic materials), and then show that by processes that should be expected (e.g., radiation, lightening) organic evolution towards life was highly probable. Another school of thought would have a series of extraordinary coincidences bring life about. Thus even if organic matter was abundant on the early Earth, it would have taken an accident, or accidents, to get organic evolution on the road to life. To illustrate the sort of disputes involved let me consider a hypothesis that requires the presence of a large moon for life to begin. Of course, if that hypothesis is right, we should conclude that life is probably very rare in the galaxy and not to be found in the solar system at all, except for our own kind.

According to this hypothesis, clays served as the templates for the amino acids to combine into the first complex organic molecules. Presumably the amino acids would be floating in shallow waters over clay surfaces, but still required a mechanism that could make them more complex. That mechanism is provided by having two amino acids form a peptide bond — a bond through which carbon and nitrogen in separate organic chains become linked. This bond can form when, for example, a nitrogen atom loses its bond with a hydrogen atom (H) and a carbon nearby loses its hydroxide bond (OH). Since the H and the OH combine to form water (H₂0), the formation of the peptide bond requires a loss of water. The problem is how to lose water in the presence of all that water in which the amino acids are suspended.

The tides created by the Moon provide the solution to the problem. When the tides go out a residue of amino acids is left on the clays, and the heavier concentration in drier surroundings allows the peptide bond to form. Once formed, the peptide bond is stable in water. After many repetitions of this process, organic molecules of an increasing complexity can be formed. The function of the clays is to provide a mechanism for replication, but that matter will wait a few paragraphs. For the time being, the issue is the role of the Moon in the origin of life.

The sun produces tides, too, but they are much smaller and perhaps not sufficient to bring about the needed peptide bonds. If a planet were closer to the star it would enjoy greater solar tides, but unfortunately it may also become locked into a very slow rotation (the Moon always offers the same face to the Earth, Mercury rotates every 58.6 Earth days, and Venus' day is longer than its year). Having a day-night cycle seems important because the opportunity to move away from equilibrium gives the pre-biological molecules a chance to vary, and this opportunity for variation is an essential characteristic of evolution. Cyclical events are in general favorable because they permit the molecules to reach a state of equilibrium to consolidate their gains before having to change again. Apart from the tides and the day-night cycle we have the concomitant temperature fluctuations. And we have seasons. Now, the Earth has seasons because its axis is tilted in just the right way. Then we must also take into account the gravitational influence of other planets, the role of the magnetosphere and many other factors whose possible relevance or even their very existence may escape the experts at this time.

Insofar as any of these are large factors in allowing life to gain a foothold on Earth, the origin of life becomes an improbable event. But we simply do not know. As plausible as hypotheses such as this may seem today, they may sound very quaint in two or three decades, let alone in a few centuries. And even if the events in question were indeed factors in bringing life into our world, on further examination they may turn out to be just some among the many alternative mechanisms that could have provided for the evolution of ever-more complex molecules in a variety of other worlds. It happens all too often that when a mechanism cannot be immediately proposed to explain a particular step on the way to life, people who ought to know better jump to the conclusion that life on Earth was an extraordinary coincidence.

Many biochemists, for example, have felt that the problem of the origin of macromolecules is insoluble. At the most basic level, life consists of nucleic acids (such as DNA and RNA) that contain the genetic information, and of functional proteins (such as enzymes). If we imagine that DNA or RNA was the original macromolecule we have to explain how it could replicate in the absence of enzymes, which are essential in modern living systems. On the other hand if we imagine that the proteins came first, how could they have built around themselves the nucleic acids that would carry the information necessary for future coding of the same proteins?

For years none of the mechanisms proposed seemed satisfactory, not even co-evolutionary mechanisms because the chemical association of nucleotides (the building blocks of nucleic acids) and amino acids (the building blocks of proteins) was just too problematic. On the face of this situation some people thought that life was a stroke of luck. And some others even suggested that life had probably come from elsewhere to the Earth, as if removing the problem of the origin of life a few light years amounted to a solution.

Nevertheless some plausible mechanisms were proposed in the late 1960s and have been refined ever since. One of them, suggested by A.G. Cairns-Smith, is that microscopic crystals in clays can serve to replicate molecules. Such clays have a large capacity for adsorption, which causes tiny bits of proteins to stick to them, just as particles of meat do to the surface of a frying pan. The crystals in these clays would then grow and reproduce the patterns of the amino acids adsorbed in the clays.

These processes can be repeated millions of times, until with the development of enzymes, as J.D. Bernal notes, we would also see the appearance of co-enzymes, some of which are identical to the nucleotides of RNA. As the co-enzymes are adsorbed, their efficiency in chemical energy transfer would give clear reproductive advantages to their associated enzymes. Under these conditions, a co-evolution of functional proteins and nucleic acids becomes possible. And this result presumably paves the road to the eventual origin of the first cells. This view has been buttressed by the work of the space scientist James Lawless, who has shown that clays do select precisely the amino acids that can form biologically active proteins.

There are many other hypotheses, many of them buttressed by experimental work that fill in some of the steps deemed necessary to take us from atmospheric gases to living cells (e.g., proteins that can "make" their own RNA) But what is necessary and what is not depends on the approach one takes to explain the origin of life. First, there are different starting points. Some want, even demand, a reducing atmosphere (poor in oxygen, rich in hydrogen and other gases like methane). Others think that the original atmosphere was composed largely of carbon dioxide. Second, then comes a story of the evolution of organic matter, a story that may involve thousands of steps, of which only some are specified. And of course, there could be alternative plausible stories. What makes them plausible is that some of the steps that may have seemed baffling at one time can be produced in the laboratory now, while others can be explained theoretically. For example, the first generally accepted story gained its plausibility from the Miller-Urey experiment, in which a reducing atmosphere in a flask was subjected to electrical discharges. Presumably the result of the experiment was a soup containing the building blocks of life. Apparently, however, only very few interesting organic molecules were actually produced in such an experiment, and those were of very little complexity. The steps from there to, say, a self-replicating molecule, let alone a cell, are truly gigantic.

Since there are so many ways to tell the story, many equally unconstrained by the scant evidence, it is not surprising that the intuitions of different investigators differ on what is crucial and what is not. And even if most of the apparently necessary steps of a particular story can be accounted for by experiments, there remains the difficulty that the answer to one part of the puzzle is often at odds with the proposed answer to the next part (e.g., a molecule used as a building block for a more complex molecule is produced in an alkaline solution, but the more complex molecule has to be produced in its opposite, an acidic environment; this is not a fatal setback, since in living things the product of a reaction can be transported to a different internal environment to be used to build something else, and in general we find that natural processes have co-evolved in the living world to accomplish just this transport, cf. the example about elephants and their environments given above). The problem is that it all seems just too convenient. What we want to know now is not just how it could have been, but how it was -- we want the "real" story.

To go from just-so stories to compelling hypotheses we need a better understanding of the initial conditions on the Earth, and as we develop our hypotheses accordingly, we will get ideas of what sorts of evidence about the subsequent evolution of the global environment we may want to look for. One helpful way to proceed is to examine those worlds where according to some approaches life might have started, or at least where we should expect some small amount of organic evolution. To the extent that organic evolution has taken place we learn much about our own, once we factor in the relevant differences. To the extent to which organic evolution has not taken place, we also learn much about the failure of some forms of reasoning about the origin of life and perhaps get some clues about more appropriate forms of reasoning.

Astrobiology and comparative planetology will merge in many other contexts. Take, for example, the search for the origin of the organic carbon on the Earth, surely a needed background to make a definitive determination of how life started on the Earth. To have organic compounds, we first need to trace the carbon and the other relevant elements (hydrogen is normally easy, since it is almost everywhere, with the glaring exception of the Moon and Mercury). We begin the search for carbon in the solar system and then see how it was apportioned to the Earth. If the Earth had a disproportionate amount of carbon, we must deal with a certain set of scenarios in which the Earth comes to occupy a privileged position. If carbon is very common in the solar system, as indeed it is, our scenarios are of a different sort, but we still want to know how the Earth came by the amounts that it has: Did it happen during the initial accretion of the planet, or was most of the carbon brought in by the subsequent cometary and asteroidal bombardment?

How do we trace the carbon in the solar system? We will look for clues in the comets and asteroids, as well as in the inner planets and all the other rocky objects of respectable size in the solar system, particularly the large moons of Jupiter and Saturn. If we wish, space exploration will make them all available to us. In the meantime we may also examine the meteorites that we do have. In some of these meteorites we find that carbon is associated with two sets of rare gases — apparently the carbon serves as a casing that keeps the rare gases trapped. When the carbon is released from the meteorite it comes out in two installments. In the first it also frees amounts of argon, krypton and xenon in relative ratios that are pretty much the same as those found in terrestrial planets. Other carbon in some meteorites, however, encases a completely different mix of rare gases (of neon, xenon, and krypton) that cannot be accounted for by any process known in the solar system. Further investigation reveals that such is the mixture that can be expected in the process by which stars become red giants. This presumably leads to the conclusion that the stellar cloud from which the solar system formed was already seeded with carbon from the death of another star.

This interplay between biology and astrophysics takes place on many fronts. As another example, we may consider the matter of extinction, which has been described earlier. The 26 million-year period for large extinctions was calculated by David Raup from the fossil records of marine animals. It was this periodicity together with the asteroid hypothesis of Luis Alvarez that led to the further astrophysical hypothesis that the sun had a companion star. Incidentally, the computer program used to estimate the effects of the Alvarez asteroid was based on a program originally developed by Brian Toon and others to study the dust clouds of Mars, and in turn served as the basis for the so-called "nuclear winter" study — which some observers still consider a reliable model of what would happen to the Earth in case of nuclear war.[2]

If such cycles of extinction are indeed determined by astrophysical events, posterity will have much reason to thank the day these combined biological and astrophysical studies were undertaken; even if the astrophysical causes turn out to be very different from those now proposed. But quite apart from preventing great disasters, the study of extinction cycles will contribute greatly to our understanding of the forces that affect the environment of the Earth.

These and other investigations underscore the intimate connections between astrobiology and those aspects of space science that deal with the formation and evolution of planets. Since the role of life has been of crucial importance for the Earth, and since we need to know specifically how terrestrial life may not only survive but also prosper, this study of origins is highly justified. To put the point differently, the biota and many of the other elements of the global environment co-evolved. Thus to understand the evolution of one of those elements we need to understand it in its relationship to the evolution of the others. Moreover, the very role of the imagination in trying to determine the range within which life can be born and the possible forms life may take provides a fruitful context in which to discuss questions of origin and evolution. For by the consideration of likely scenarios for life, and by the comparative examination of the planets in our solar system and of other planetary systems, we will be better able to understand not only how life came about but also why it took the paths that it did when it apparently had others available.

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[1]. Although the emphasis has been mine all along, in making these remarks I find myself paraphrasing Harold P. Kline's many comments on earlier drafts of this essay.

[2] R.P. Turco, O.B. Toon, T.P. Ackerman, J.B. Pollack, C. Sagan, "Nuclear Winter: Global Consequences of Multiple Nuclear Explosions," Science, 23 December 1983, Vol.222, P.1293. See also O.B. Toon et al, "Evolution of an Impact-Generated Dust Cloud and its Effects on the Atmosphere," Geological Society of America, Special Paper 190, 1982, p.187.

ALH84001 and Occam’s Razor

Chapter 6C

ALH84001 and Occam’s Razor

In the case of Mars, the hypothesis has been much strengthened by David McKay’s team’s analysis of the Martian meteorite known as ALH84001.[1] According to this analysis, the meteorite contains globules of carbonate, polycycle aromatic hydrocarbons (PAHs), magnetite and iron sulfides, and some intriguing structures that some believe might be the fossils of ancient Martian bacteria. We know that the meteorite, which was found in Antarctica, came from Mars because the air trapped inside exhibit the same mix of rare gasses that the Martian atmosphere has. Great care was taken to rule out the possibility that the organic materials found could be the result of contamination (a claim buttressed by the fact that the proportion of those materials increases towards the center of the meteorite). Nevertheless the reaction to McKay’s results, particularly by those scientists considered experts on meteorites, was extremely hostile.[2]

The motivation for the hostility was in no small part the fear of subjecting to ridicule the subdiscipline of planetary science devoted to the study of meteorites, to let it fall into the pit of another “cold fusion,” the big scientific embarrassment of a few years previously. The main argument against McKay’s analysis was methodological. It was based on Occam’s razor, a principle named after William of Occam, the medieval philosopher who insisted that we should accept the simplest explanation available:

All the compounds and structures found in ALH84001 could have been produced by inorganic processes. Therefore, by Occam’s razor, we should eliminate the unnecessary conclusion that we have found evidence of alien life.

As it was often repeated during the debate about ALH84001, extraordinary claims require extraordinary evidence, but hydrocarbons, the magnetite and the minute worm-like features could be explained by ordinary inorganic processes. There is presumably, then, no need to conclude that Martian life caused the phenomena found in the meteorite.

Occam’s razor, however, does not rule against McKay’s analysis. For what we have is a collection of three things in an extremely confined space (a few nanometers across): (1) typical bacterial food (hydrocarbons), (2) structures that look like typical bacteria, and (3) typical excreta of bacteria (magnetite and iron sulfides). One simple hypothesis, life, accounts for all these phenomena and the fact that they are closely packed together: Martian bugs ate the hydrocarbons and left the droppings behind. The inorganic-origins hypothesis requires at least three separate mechanisms and has little to say about why they are together in such a small space.

Some of the strongest criticisms have been made against the claim that the worm-like structures are fossils. Critics have argued, for example, that those structures formed under too much heat (but other studies support McKay on this point). But the most telling criticism was that the structures were much too small to be able to carry out many important organic functions— they came in at less than one-hundredth the size of terrestrial bacteria. This leads to a very important point I will discuss below. For now let me say that, even if those structures are not fossils, the life hypothesis is still more economical: Martian bugs ate the hydrocarbons, left their droppings, but then failed to fossilize — which is perfectly understandable for soft cells. Moreover, inorganic magnetite forms at a temperature about three times higher than that apparently experienced by the Martian meteorite. And to make matters worse, the magnetite in the sample, unlike that produced by inorganic processes, is of an extremely pure form, which on Earth is normally produced only by bacteria. It is far from obvious then that the inorganic-origins hypothesis is simpler. Occam seems to smile on the life hypothesis instead.

This is not to say that I favor the life hypothesis. For I do not believe that a matter of such significance can be decided by one single methodological point -- Occam’s razor. In any event, there seems to be little doubt now that Mars has had organic carbon, and that is a great find after the discouraging results from the Viking experiments. The sensible way to proceed -- and both sides of the controversy seem to agree on this point -- is to go back to Mars and look for evidence of fossils in places naturally protected from ultraviolet radiation.

The prospects for Europa also look good, now that the favored view is that all the origin of life requires is an environment with plenty of liquid water, organic carbon and a source of energy. Europa is ten percent water, much of it apparently in an ocean under the ice; it should have plenty of organic carbon because of its location in an area of the solar system rich in organics; and it obviously has a reliable source of energy, otherwise it could not continue to smooth out its icy surface. Let us be cautions, though, about the prospects for life on the watery moons of the outer planets, Europa for example.[3] It is not enough to have around liquid water, simple organic compounds, and a source of energy. Metals such as iron, zinc, copper, nickel, cobalt, magnesium, and manganese performed catalytic and other crucial roles in terrestrial organic evolution, as they do in the normal functioning of cells today. Without most of those metals the prospects for life in any of the outer moons would be very dim. And so we must ask whether Europa is likely to have them. The answer is yes. Europa is one of the few outer moons with a density (3.0) close to that of our Moon (3.3). Indeed the rocky core of Europa under the watersphere would have a density even closer to the Moon’s. It is a good bet, then, that it would offer a variety of metals similar to that of the Moon — and this is enough to keep Europa as one of the leading candidates in the solar system to harbor alien life.

If we never find life, or fossils of life, in Mars, Europa, of anywhere else in the solar system, astrobiology will have to look at other solar systems for specimens. Unfortunately a mission to the stars would last tens of thousands of years with the technology we can muster today. And even with the best space technology that we can plausibly envision for the next century, it would still take hundreds of years to travel to another solar system. Perhaps fancier technologies (to be described in the next chapter) can get us there faster, but those technologies will not be around in the near future. There is a shortcut available to astrobiology, and that is to make contact with intelligent extraterrestrial life. But that is a long shot, as we will see in Chapter 8.[4]

Nevertheless, even if we find no alien life in the solar system, the pursuit of astrobiology will continue to be worth our while, as we will see in a soon-to-come posting.

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[1] D.S.McKay et al, “Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite AL84001,” Science, Vol. 273, 16 August, 1996, pp. 924-929.

[2] See R.A. Kerr, “Ancient Life on Mars,” ibid., pp. 864-866. The controversy spread to public arguments in the newspapers; see for example the front page article “Life on Mars: Scientists ‘thrilled’ by prospect,” Seattle Times, August 7, 1996.

[3] Other rocky moons with possible oceans include the gigantic Jovian moon Ganymede: R. Cowen, “Ganymede May Have Vast Hidden Ocean,” Science News, Vol. 158, December 23 & 30, 2000, p. 404.

[4]. For a fuller treatment of this issue see Chapter 8.

The (so far) Unsuccessful Search for Life in the Solar System

Chapter 6B

The (so far) Unsuccessful Search for Life in the Solar System

Given this apparent potential of astrobiology, then, it is not surprising, that the Viking missions to Mars in the 1970's created great hopes of a scientific bonanza. In those missions we could for the first time examine a world where life might exist. Moreover, the harsh Martian environment offered the possibility that if life had evolved there it would be radically different from Earth's. Thus when the first experiments carried out by the robot landers seemed to indicate that photosynthesis was going on, which presumably only living things can perform, the excitement was deservedly extraordinary. But the excitement soon led to puzzlement when a chemical experiment determined that the soil possessed no organic carbon (C-H bonds). The fundamental chemistry of life simply was not there. And therefore neither was life. Now this is the way the story was told at the time and for many years after. Today, several developments have changed the picture considerably. To see the importance of those developments, let me present the picture of the post-Viking landings as it stood for almost 30 years.

The result of the Viking chemistry experiment was very disheartening to many. We find organic matter in meteorites, in comets, even in deep interstellar space. How can Mars be so utterly deprived? Experiments by Stanley Miller and others have shown that some organic molecules form easily in the presence of gases that might have existed on both the Earth and Mars shortly after their formation (essentially, Miller mixed methane, ammonia, and hydrogen in a jar, subjected the mixture to electrical discharges, and then analyzed the goo that grew in the water, which yielded some amino acids and other organic compounds).[1] It is possible that in Mars those gases did not meet in any convenient ratios, but it must be said that the nature of the Earth’s primordial atmosphere is a matter of dispute. In some scenarios, that atmosphere was dominated by CO_2, which would not respond to a Miller type of experiment by producing organic compounds. The terrestrial air of today, to mention another illustration, when subjected to discharges of electrical energy, produces smog, not the organic soup of the classical Miller experiment. Even so, if we drastically reduce the free oxygen and vastly increase the concentration of hydrogen in today's air, organic compounds will still form in a Miller type of experiment. Why was life so unlucky on Mars?

At the time many suspected that the Viking missions did not offer such a grand opportunity for exobiology after all. The density of the Martian atmosphere is so low that liquid water could not now exist on it. This presents at least two problems for life. The most obvious one is that it is difficult for life to get by without liquid water — although perhaps the permafrost detected on the surface of Mars might suffice to sustain certain kinds of microbial life under the rocks.[2] The second is that when the permafrost is heated by sunlight it becomes water vapor. As the water vapor rises in the atmosphere, it is subjected to ultraviolet radiation, which disassociates the molecules of water. The freed light hydrogen atoms are eventually lost to space (Mars is surrounded by a gigantic envelope of hydrogen). The heavier oxygen could be expected to react with the substances in the soil. As we saw in Chapter 4, oxygen was a poison to earlier forms of life, precisely because it reacts so easily to form compounds. The oxidizing Martian soil would make it very difficult for organic evolution, let alone life. To make matters worse, Mars has no ozone layer and thus the ground is constantly bathed by ultraviolet radiation. All in all, some even claimed, the surface of Mars is far more antiseptic than the most fastidious operating room on Earth.

Furthermore, the Martian atmosphere shows no signs that its chemistry is being altered by the presence of living organisms. The Earth's atmosphere, by contrast, has far less carbon dioxide and far more oxygen that can be accounted for by physics and chemistry alone. Indeed, as we saw in Chapter 4, the composition of the Earth's atmosphere indicates that it is not in chemical equilibrium. And according to Margulis and Lovelock, the atmospheric gases can be kept so far from chemical equilibrium only through the action of living organisms, especially that of bacteria.[3] On the basis of this reasoning, by the mid-sixties Lovelock had predicted that no life would be found on Mars.

But is life on Mars truly impossible? Some exobiologists argued at the time that the results of the Viking experiments do not warrant such a conclusion. They tried to meet the objections drawn from the chemical experiments in the following way. First, they pointed out that life would not alter the Martian atmosphere substantially if it only existed on the margins, so to speak. Small colonies of small organisms might sustain themselves without exerting pressures on the rest of the Martian environment large enough for detection with telescopes and the Viking state of the art. Second, the unprotected surface is not the place to look. There are sites in Antarctica devoid of life on the surface, but if we care to dig we may find it in porous rocks below. Third, these exobiologists brought up numerous examples of life surviving under extreme conditions: in the core of nuclear reactors, in underground streams with temperatures of hundreds of degrees Fahrenheit, under incredible pressures at the bottom of the ocean. Organisms have been found even deep in the Earth's crust. No extreme habitat, though, is as challenging as the Don Juan Pond in Antarctica, where the salinity is so great that a random sample is likely to fail the Viking test for the presence of carbon compounds. But living organisms exist there! [4]

The claim of these exobiologists was that the Viking experiments were designed to detect average life, whereas it is clear that if any life exists on Mars it should be in extreme forms. Mars is an extreme habitat, if it is a habitat at all; experiments should be designed and interpreted accordingly. Furthermore, if life cannot be entirely ruled out on Mars, we can hope, however dimly, to find it where organic matter is plentiful: in the outer solar system. We may imagine that if life can adapt to such inhospitable habitats on Earth, it might be able to make a stand in the organic clouds of Jupiter or perhaps in some underground caves in active Io. Another moon of Jupiter, Europa, is covered by smooth ice, which indicates a good amount of internal heat. This makes Europa particularly interesting to exobiologists because under the ice there appears to be an ocean of water. Another notable prospect is Titan, the large moon of Saturn with a dense atmosphere and at least traces of organic compounds. Unfortunately Titan is too cold for life as we know it — cold enough (-288 F°) that the argument about the ability of life to adapt to extreme habitats begins to wear thin.

In any event there is a serious problem with this argument. The evidence presented can show only that once life begins it can adapt to very hostile conditions. But it does not show that life could begin in such conditions. These are two very different things. Let me illustrate this point by means of an analogy. During pregnancy, many substances can be lethal to the developing embryo, e.g., alcohol, tobacco, and hallucinogenic drugs. The chances for the new life are greatly hampered under those conditions. Once the baby is born, the situation begins to change. Eventually it may grow into an adult who smokes, drinks and abuses drugs, none of which are conducive to a healthy life, but none of which need be immediately lethal either, as they could be to the embryo. Also, life might not be able to make a start on a planet that would otherwise be exactly like today's Earth; but it surely has no trouble flourishing in it now. And as far as I know, most of the scenarios considered favorable to the birth of life are at odds with the extreme habitats of these examples. It is difficult enough to figure out how life started on Earth, as we will see presently, without the complications posed by such extreme environments. On this point we require further argument from these exobiologists of old and astrobiologists of new.

As far as Mars is concerned, however, the angels are with them. For if the Martian atmosphere was at one time much denser, life might have indeed begun; and then it might have survived, gone hail or high water. These hopes are sustained to a large extent by the tantalizing possibility that, once upon a time, Mars was far warmer and wetter, a possibility indicated by surface features that resemble river deltas and by dendritic channels also similar in appearance to river systems on our planet. These channels presumably constitute evidence of running water. As we saw earlier, in a thin atmosphere, such as the present Martian atmosphere, water goes from solid to vapor without first becoming liquid. Therefore, this evidence of running water is in turn evidence that the atmosphere was much denser once upon a time.

There are alternative hypotheses on the dendritic channels, though. According to one of them, for instance, occasional but pronounced tilts in Mars' axis of rotation would expose one of the poles to the full action of the sun. If that were the case, the melting polar cap would provide enough pressure to permit water to run off and presumably form those surface features -- all without the benefit of a dense atmosphere.[5] Photographs by the Mars Reconnaissance Orbiter, with ten times better resolution than any taken before, indicate that lava and wind-driven dust have run through those presumed river channels and gullies far more recently than water, even though catastrophic floods might have carved them once upon a time.[6]

Nevertheless the preponderance of new evidence indicates that the Martian atmosphere was far denser once upon a time and that liquid water ran on the Martian surface. The most striking findings are those of Opportunity, a Mars Exploration Rover. Opportunity found, for example, salt deposits in a region called Meridiani Planum. According to Mike Carr, the man who wrote the book on water on Mars, it is clear that a large body of water existed in that region. It is also clear that the “water had to pass through the ground to pick up the dissolved ions that ultimately were precipitated out as salts.”[7] This means that the water in that region (a lake or a sea) could not have been mere runoff from melted polar ice.

If we assume that planets similar to the Earth have similar beginnings -- in this case similar distributions of organic materials, atmospheric gases, and sources of energy -- and if we keep in mind that our own earliest fossils are about 3.5 billion years old, it seems plausible to suppose that life made a start in Mars. If that is so, the possibility exists that in some regions of Mars we may find fossils of organisms that thrived in days when the atmosphere was denser and warmer.

Although such Martian fossils would perhaps not be as exciting as living organisms, they still would be invaluable in that they would permit us to compare our form of life with an alien one. We may also be able to draw some interesting lessons from a failed interaction between life and a planetary environment.

As luck would have it, though, liquid water is likely to exist in underground deposits. The permafrost is presumed to exist to a depth of hundreds of meters, which suggests that some of water will be found in temperatures high enough to keep it liquid, if nothing else because of proximity to magma deposits and other sources of thermal energy. Martian life forms, if any exist, need not be quite as extreme after all.

Incidentally, it seems to me that the reasoning that would lead us to hope for fossils in Mars might also lead us to hope for fossils in Venus, as long as we assume that it took the greenhouse effect several hundred million years to run away and vaporize the oceans. Such Venusian fossils (or perhaps even living organisms!) would have to be found well below the surface, away from the poisonous atmosphere, just as their counterparts on Earth to whom oxygen is a poison. Most likely, though, the active geophysics of Venus, as well as its high internal temperature, would have destroyed any fossils in the rocks. 600 million years ago, the entire surface of Venus is supposed to have melted by internal processes that surely would have obliterated even the hardiest of bacteria. At any rate, looking for fossils in Mars should be far more pleasant than in a place where lead would run liquid and the clouds rain sulfuric acid.

These arguments do not establish that extraterrestrial life in the solar system is likely. All they establish is that we cannot rule it out completely. But we should remind ourselves that in order to make a case for the possibility of life in Mars or Europa, we must assume either that an extreme environment is not barrier to the origin of life or that organic evolution is likely on an environment similar to that of the early Earth. This second assumption, taken as a testable hypothesis, is what makes the search for life in Mars and Europa a reasonable enterprise.

In the case of Mars, however, such an enterprise changed from reasonable to exciting when we were lucky to receive a gift from the heavens, which will be the subject of the next posting.

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[1]. For a very accessible account of the classic Miller-Urey experiment see D. Goldsmith and T. Owen, The Search for Life in the Universe, Benjamin/ Cummings Publishing Co., 1980, pp. 174- 177.

[2]. Several alternative liquids have been proposed, especially ammonia and methyl alcohol. Goldsmith and Owen offer a very accessible account of this matter also (ibid. pp. 212-216). For more technical literature the reader may consult the appropriate titles in Note 8.

[3]. L. Margulis and J.E. Lovelock, "Atmospheres and Evolution," Life in the Universe, John Billingham, ed., NASA cp.2156, 1981, p.79.

[4]. For this point of view see p. 5024. S.M. Siegel, "Experimental Biology of Extreme Environments and Its Significance for Space Bioscience," Spaceflight, ____, p. 128; Siegel et al "Experimental Biology of Ammonia-Rich Environments: Optical and Isotopic Evidence for Vital Activity in Pennicillium in Liquid Ammonia-Glycerol Media at -40 C," Proceedings of the National Academy of Sciences, Vol. 60, No. 2 (1968), p. 505; S.M. Siegel and T. W. Spettel, "Life and the Outer Planets: II. Enzyme Activity in Ammonia-Water Systems and Other Exotic Media at Various Temperatures," Life Science and Space Research, 15 (1977), p. 76; B. Z. Siegel and S.M. Siegel, "Further Studies on the Environmental Capabilities of Fungi: Interactions of Salinity, Ultraviolet Irradiation, and Temperature in Penicillium," Gospar Life Sciences and Space Research, Vol. 8, R. Holmquist, ed., Pergamos Press (1980), p. 59.

[5]. Science on radial shift as cause of dendritic channels

[6] Science, Vol 317, September 21, 2007. “Special Section: Mars Reconnaissance Orbiter”, pp. 1705-1719.

[7] M. Carr, “The Proof is in: Ancient Water on Mars,” The Planetary Report, Vol. XXIV, No. 3, May/June, 2004, p.11.

THIRD CHALLENGE: SPACE BIOLOGY

Chapter 6A

THIRD CHALLENGE: SPACE BIOLOGY

The well-being of human life has been the ultimate justification for the physical branches of space science. But can we justify the space science of life itself? What is the value of doing biology in space? Many observers, space scientists included, do not think highly of the scientific prospects of the field. The main purpose of this and the next few postings is to meet their objections, to show that the study of life in space also shows the serendipitous, deep practicality of the other space sciences.

Space biology can be roughly divided into two main areas. The first investigates the possibility of extraterrestrial life; it goes by the name of exobiology, or, more recently, astrobiology. The second investigates the behavior of terrestrial life in outer space; it corresponds to the idea most laymen have of space biology[1]. Since these two areas are distinct, they require separate analysis and separate justification.

Exobiology/Astrobiology

Introduction.

It used to be said with derision that exobiology is a science without subject matter. We have never found any alien life, and for all we know terrestrial life might be the only life in the universe. Or even if there is life somewhere else we might never find it. Or if we stumble upon it by chance, we might not recognize it as life.

Exobiology did have its moment of fame in 1975 with the Viking missions to Mars; but, after the Viking landers failed to find life, the field steadily declined in prestige and seemed moribund until two extraordinary developments resuscitated it.

The first was the dramatic advance in the search for planets around other stars. In the last few years hundreds of extraterrestrial planets have been discovered, most of them gas giants even larger than Jupiter, but we are also beginning to find rocky planets a bit larger than the Earth. This development was extraordinary because even the best telescopes were not expected to take pictures of planets many light years away from us. Some researchers had claimed to detect the presence of large planets by the wobble they caused on the paths of their parent stars, but it was generally agreed that such “wobble” was comfortably within the margin of error of the observations. Researchers hoped that a generation of space telescopes yet to come might help, until some clever astronomers invented a completely novel approach: the tug and pull of a planet on a star, if they are both on our line of sight, will make the star move away or toward us. That means that the star’s light would be shifted towards the red, if the star is moving away from us, or towards the blue if it is moving towards us. Spectral analysis, thus, has made the discovery of new planets routine. The planets found so far are very close to their stars, even closer than Mercury is to the Sun, but that is not to say that all extraterrestrial planets are that close. It should be expected that the first planets we found by measuring how much their gravitational pull disturbs their stars’ orbits should be precisely those that are very close to their stars. All these discoveries have been supplemented by the observations, with infrared telescopes mostly, of planetary systems in formation – observations that make plausible the existence of terrestrial planets throughout the galaxy.

The second extraordinary development was the discovery of organic compounds in a Martian meteorite (ALH84001), and the tantalizing suggestion that some worm-shaped structures found inside might be fossils of extremely small Martian bacteria. The monumental excitement created by the announcement led to a very ill-tempered controversy between groups of scientists that I will discuss later in this section. Both sides would agree, however, that the discovery of extraterrestrial life would give us good reason to get excited. For by comparing terrestrial and extraterrestrial life we would learn much about our own life and our own planet.

We can readily see that the possibility of such a comparison may provide an excellent motivation for the pursuit of exobiology, and so this will be the first issue I will discuss. I will then examine the negative results of the search so far and evaluate the hope created by the Martian meteorite. And, finally, I will determine why it makes sense to continue doing astrobiology even in the face of uncertain results.

1. The Motivation for Astrobiology

What would extraterrestrial life enable us to learn about our own kind of life? The answer is clear. All life on this planet is based on the same carbon chemistry and apparently all have the same genetic code. Of the many possible amino acids, only twenty are used to build proteins. DNA, the reproductive code for terrestrial life, makes use of only four bases. Moreover, organic molecules can be left handed or right handed, but terrestrial life prefers left-handed amino acids and right-handed sugars. Are these circumstances mere accidents of organic evolution, or are there fundamental reasons why life has taken these particular turns on this planet? Even one other kind of life would permit us to make great strides in examining these matters. For that other life may use a wider range of amino acids and bases, or it may prefer right-handed amino acids or left-handed sugars. One result of such a finding may be that, say, a particular chemical balance in the Earth’s oceans caused the preference for left-handed amino acids. Or the alien life may be similar to life on Earth, which would reveal to us some sort of organic inevitability. In either case, if we have knowledge of the natural environments of that alien life, we can begin to understand why certain paths open to organic evolution are conducive to replication. The new perspective would be very fruitful in trying to understand our own biology at all levels.

It would be especially useful to observe stages of organic evolution and to study life as it begins in a new world, or at least to find fossil records of such beginnings. Beyond the stage of primitive cells, radically different alien forms of life would still offer great rewards, as we will see below. Even if perchance organic evolution produced in two similar planets similar primitive cells with essentially the same genetic code, the subsequent evolution would have much to teach us, for life in those two planets would undergo different histories of adaptation. Imagine, for example, that the now famous Alvarez asteroid had not crashed on the Earth. No one knows how dinosaurs would have continued to evolve, but it is possible that their grip on the surface of the planet would have been further strengthened. Mammals might have been thus forever condemned to crawl and scratch in the night like so many other vermin.

Even similar planets are likely to exhibit different tectonic histories. Plate tectonics brings continents together or breaks them apart; it throws chains of mountains up over the landscape; and it creates volcanoes where the plates rub against each other. In doing so it brings some habitats to an end and others into existence; it destroys; it influences; it changes life in many ways. Consider how the variation in the size of landmasses influences the fauna and flora of a planet. Certain large animals, for example, need a large environment in which they can roam for long distances. Elephants used to travel many hundreds of miles in their annual migrations. As these big mammals went along, they ate a variety of plants, thus insuring a balanced diet and permitting the vegetation at every feeding stop enough time to recuperate. Their considerable droppings were recycled, in the meantime, by armies of insects and bacteria. In a much smaller environment the vegetation would have been devastated, and the elephants would have suffered from poor diets and the unsanitary rot of their own excrement.[2] They would not have been fit.

Slight differences at the beginning of the history of a planet would alter the make-up of the crossroads that life has to face, first at the level of organic chemistry, and then at the level of cells — presuming that cells are common to living things. A eukaryotic cell (a cell with a nucleus) may well be the result of symbiosis between different varieties of prokaryotic cells (without a nucleus).[3] For example, the mitochondria in eukaryotic cells (see Figure 1) may be the remnants of prokaryotic cells that discovered how to use oxygen for energy and were swallowed but not digested by larger bacteria. Since eukaryotic cells are the building blocks of all complex organisms on Earth, we can imagine that different symbiotic relationships between primitive cells might have led to forms of life vastly different from those of our acquaintance. On planets so endowed, the subsequent interaction of life with the rest of the environment would have a multiplier effect, for they would change their environment in novel ways, and those new environments would lead life to adaptations that on Earth could meet only with misfortune.

Acquaintance with such alternative biotas would inevitably lead to profound transformations in biology, since biology would grow, and scientific knowledge seldom grows without changes. In this, scientific knowledge resembles animals. Mammals, for example, did not just get bigger after the extinction of the dinosaurs. As their size increased, the structure of their skeletons had to change to accommodate their larger weight. In a planet with gravity similar to ours, a dog the size of an elephant would probably look much like an elephant. In an analogous manner, a science of biology that were suddenly much larger in subject matter would have to grow connections and supporting structures for which there was little need in the days of a single biota.

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[1]. I do not divide the field in the manner that NASA has found convenient for a variety of administrative reasons (according to which, for example, Space Biology is only a small section of the Life Sciences Division). My division follows rather the convenience of the argument and of the reader.

[2]. Adapted from R.M. Laws, I.S.C. Parker, and R.C.B. Johnstone, Elephants and their Habitats, Clarendon Press, Oxford (1975).

[3]. For an informal, though detailed account of these issues see Gene Bylinsky, Life in Darwin's Universe, Doubleday, 1981.