But there’s a catch. Fluorine yields a big helping of energy on combining with hydrogen and that means that it is that much more difficult to break up hydrogen fluoride into hydrogen and fluorine.

  Plants on earth break up water by using the energy of red light. To break up hydrogen fluoride, red light would not be energetic enough. Blue light would be necessary; perhaps even the near ultra-violet.

  This makes things tricky. If the sun is close enough or hot enough to provide this more energetic light in sufficient quantity, it might make the temperature of the planet hot enough for a hydrogen fluoride ocean to be impossible. If the sun is far enough or cool enough to allow the hydrogen fluoride ocean to exist, there might not be enough energetic radiation to allow fluorine-type photosynthesis to take place.

  In all these cases, by the way, the effect on the composition of tissue constituents is profound, but I am deliberately neglecting that. I’m not even thinking about it. That’s for some other occasion some other day. Sufficient unto this day are the atmospheres thereof.

  So far, we have been replacing the oxygen atoms of our familiar water-oxygen cycle. What if we leave them alone and replace the hydrogen atoms instead? Sulfur is the only substitute I can think of. In the range from 393 to 718, we can have a sulfur dioxide atmosphere and a liquid sulfur ocean. Plants would breathe in the sulfur dioxide, break it up into sulfur and oxygen and store the oxygen in their tissues.

  Animals would eat the high-oxygen plants, drink the liquid sulfur and belch out sulfur dioxide. The beauty of this is that the combination of sulfur and oxygen yields as much energy as the combination of hydrogen and oxygen.

  Another possibility involves not an element but a compound, carbon monoxide (CO). Carbon monoxide will substitute for hydrogen since it will combine with oxygen to form carbon dioxide, yielding sufficient energy, too. The only trouble with that is that carbon dioxide is a liquid over only a very small temperature range, 20 degrees or less and then only under pressures at least 5 times as high as that of our own atmosphere. Arranging to have a carbon dioxide ocean is too tricky to be practical.

  This may cause you to think what about using other and more complicated compounds—a carbon monoxide-formaldehyde system; or a cyanogen-hydrogen cyanide system. Well, the more complicated you make a system, the more you’ll have to sweat justifying it, and the less likely you are to meet it anywhere in the universe. The same goes for systems where both hydrogen and oxygen are replaced.

  I will leave the problem of making up atmospheres at that level of complication and improbability to the reader.

  I would like to mention, though, before leaving the matter, one atmosphere system that I think is more probable than any I have yet mentioned in this speculative half of the chapter.

  The system is a reverse water/hydrogen-oxygen system.

  Imagine a planet the size of Uranus in the position of Mars. It has just managed to hang on to enough hydrogen to allow it to be a major component of the atmosphere, along with ammonia, methane and carbon dioxide, and yet the planet is just warm enough to allow the presence of liquid water.

  Plant life on such a world might split water to hydrogen and oxygen. It would then combine oxygen and methane (which it breathes) to form starch, liberating the hydrogen into the atmosphere. The methane would be replaced by hydrogen; the carbon dioxide would be reduced to methane and then replaced by hydrogen; the ammonia would stay put. The atmosphere of the world would end as only hydrogen and ammonia.

  Animals would eat the starch, breathe the hydrogen, recombine the oxygen of the starch with the hydrogen to form water, and breathe out methane gas.

  Our situation, exactly, but in reverse.

  With which thought, and with my head humming slightly, I’ll step out into the back-yard to take a deep, invigorating breath of oxygen and stare fondly at the grass which is so busy making more of it.

  NOTE

  In the twenty years since this was first written (July 1956) astronomers have discovered more about the details of planetary atmospheres than they had in all of time previously—thanks to the coming of the space age and of the launching of satellites and probes. However, the material in this article remains essentially correct. For further details on the evolution of atmospheres, particularly on Earth, please see my article “Our Evolving Atmosphere” which you find as chapter 13 in my book Is Anyone There? (published in paperback form by Ace Books.)

  CHAPTER SEVEN—THE UNBLIND WORKINGS OF CHANCE

  The question for discussion is exactly how much luck was involved in the development, on Earth, of life from non-living substances, and, as a corollary, what chance there is of finding life on any other Earth-like planet.

  To go about this systematically, let us first decide what (from a chemical standpoint) non-life is, and what (from a chemical standpoint) life is, and then, perhaps, we can see how non-life may turn into life.

  Non-life first—and specifically the ocean.

  The ocean consists, chiefly, of course, of water. Secondly, it contains dissolved ions (that is, electrically charged atoms or groups of atoms). The chief ions are sodium ion and chloride ion, but substantial quantities of potassium ion, calcium ion, magnesium ion, sulfate ion, phosphate ion and others are also present. These are all substances that exist in the ocean today and, we have every reason to believe, existed in the ocean before life began, though probably in lesser concentration then.

  But the primordial ocean contained more than water and ions. It contained gases in solution, derived from the atmosphere. So does today’s ocean, to be sure, but the primordial atmosphere was different from today’s atmosphere and the dissolved gases in the primordial ocean were different, therefore, from those in today’s ocean.

  The nature of the atmosphere of the primordial Earth in the days before the coming of life was discussed in the last chapter. The conclusion was that Earth’s atmosphere then consisted primarily of ammonia (NH3) and carbon dioxide (CO2). Ammonia is extremely soluble in water and carbon dioxide is fairly soluble. Both gases would occur in quantity in the ocean.

  Minor constituents of the early atmosphere would be hydrogen sulfide (H2S), methane (CH4) and perhaps even some hydrogen (H2) which had not yet had time to leak away into space. Of these, hydrogen sulfide is somewhat soluble, but the other two are only slightly soluble in water. Still there is so much water in the ocean, that the total dissolved quantity of even a slightly soluble gas comes to volumes that must be measured in cubic miles.

  There we have non-life. The substances mentioned in this section are the non-living raw materials of life.

  Which means I must now turn to life.

  The living cell (of the human being, say) is an exceedingly complex mixture of substances, any one of which, if isolated in a test-tube, is no longer alive, or at least does not possess the properties we commonly associate with life. This might lead us to believe that life is something more than a chemical or a group of chemicals—and to a certain extent, I suppose that is correct.

  Yet not entirely correct. Some of the chemicals in the cell are more nearly associated with life than are some others. For instance, in the interior of the cell is a denser portion, marked off from the rest by a thin membrane. This denser portion is called the cell nucleus. It is the cell nucleus which organizes the growth and reproduction of the cell so that if we were to try to pin life down to something smaller than the cell, it would be at the nucleus that we would have to look.

  Within the nucleus there is chromatin material which, during cell division, coalesces into a number of threadlike objects called chromosomes. There is a tremendous quantity of evidence to the effect that it is these chromosomes that determine the chemical characteristics of the cell of which they form a part. During cell division, each chromosome duplicates itself meticulously so that each daughter cell gets a full set of accurate chromosomes.

  It becomes reasonable to suppose that life is most closely associated with the chromosome portion of the cell. As material evidence for that, consider the sperm cell, which is just a tiny, tailed bag, containing a half-set of chromosomes and nothing else. Yet not only is the sperm cell alive but it carries within it the chemicals controlling the thousands of hereditary characteristics that are transmitted from father to child. (The other half-set of chromosomes is contained in the ovum so that father and mother contribute equally to the chemical characteristics of the child.)

  We can go further still. The chromosomes (on the basis of indirect, but extremely detailed and convincing, evidence) are strings of genes, each gene controlling an individual inherited characteristic. (To supply a musical metaphor, the individual gene strikes a single note; while all the genes of all the chromosomes of an individual cell sound the complex symphony we call life.)

  The gene, we think, is a single molecule; extremely complex, it is true, but still a single molecule of the type known as nucleoprotein.

  And that is as far down as we can trace life within a cell.

  Let’s try another tack. So far we have been looking deeper and deeper into a complex cell. Suppose that instead we look for simpler and simpler cells. Would that help?

  Unfortunately, simple cells don’t exist. Animals that are smaller and less ‘advanced’ than man may have fewer cells and fewer different kinds of cells and less specialized cells, but each individual cell remains just as complicated (chemically) as ever. Even the single cell of the bacterium is not simple. It is, if anything, more complicated than the cells of a human being, and contains all the different kinds of chemical substances a human cell does.

  But there are objects which are subcellular in size, yet which are considered to be alive. Those objects are the viruses.

  Viruses come in a variety of subcellular sizes. The larger viruses are still fairly complicated and contain a variety of chemicals, but as one considers smaller and smaller viruses, they appear to strip themselves of one type of chemical after another, hanging on, presumably to the more essential, then, finally, only to the most essential.

  The smallest viruses of all are made up of single molecules of one particular substance—nucleoprotein.

  So we reach life-at-its-simplest by two routes and come up with genes in one case and viruses in the other, and both are nucleoprotein.

  Do nucleoproteins possess any properties which mark them out from other chemicals? Is there anything about them to suggest why they should be so intimately connected with what we call life?

  In one respect there is. Nucleoproteins, in their natural surroundings, have the ability to reproduce themselves. The genes within the cell, for instance, can somehow cause simpler substances in the surrounding fluid to line up in such a way that atom for atom the final arrangement resembles the atom arrangement in the molecule composing the gene. This line of simpler substances is then knit together to form one huge, complicated molecule—the duplicate of the gene which served as a pattern. This is called autoreproduction and, of all known substances, only the nucleoprotein is known to possess the property.

  The gene can bring about the synthesis, not only of a second molecule of itself, but also of somewhat less complicated molecules (perhaps modeled on limited portions of itself) called enzymes. These enzymes govern the chemical reactions within the cell and, in this way, dictate the cell chemistry. Each gene is responsible for the production of a few specific types of enzymes (perhaps even of only one type of enzyme).

  The virus can be looked upon as an independent gene (or group of genes) which can invade cells and run them to suit itself. It is like the cuckoo which lays its eggs in the nests of other birds. The virus, within a cell, superimposes its own chemistry, by some means, upon the cellular victim. It forms its own type of enzymes and duplicates itself over and over again out of the simpler substances within the cell, and all the cell’s normal functions are suspended indefinitely under the stress of the foreign demands.

  The method by which a nucleoprotein multiplies itself and ‘grows’ must be distinguished from the way in which a crystal ‘grows’. As a solution of sodium chloride slowly evaporates, sodium chloride crystals form and increase in size. They increase in size because as sodium ions and chloride ions come out of solution, they align themselves on existing crystals according to the pattern of electrical charges on the crystal surface. There is no change in the ions in the process. They were ions in solution and they’re ions in the crystal. They’re bound to one another by the same forces that bound them in solution. It is just that there is order in the crystal where there was none in solution. There is increased organization in the crystal.

  The nucleoprotein molecule, however, does not merely find more nucleoprotein molecules in its neighbourhood to add on to a conglomeration of itself. It starts with different substances altogether, much simpler than itself, and brings about the formation of another ‘itself’.

  The increase in organization involved in a nucleoprotein duplicating itself is much higher than that involved in a crystal of sodium chloride growing larger.

  In fact, one might try to define the ‘livingness’ of a substance or conglomeration of substances as a measure of the rate at which it can increase the organization of its surroundings and the level of organization it can reach.

  Now, then, we can come to a conclusion. If we can deduce how a nucleoprotein molecule might have been formed from non-living material—even just one nucleoprotein molecule—then all the rest of the development of life from that single nucleoprotein becomes understandable.

  To paraphrase a famous saying: Nucleoprotein is the whole of life; all else is commentary.

  We’ve managed to define the problem in its simplest terms, now. On the side of non-life, we have a lot of water, considerable carbon dioxide and ammonia, a small quantity of hydrogen sulfide, and a bit of methane and hydrogen, plus the ions in the ocean. The atoms included in the molecules of these substances are a lot of hydrogen atoms, a considerable number of carbon atoms and oxygen atoms, a sizable number of nitrogen atoms and a small number of sulfur atoms. Among the ions are phosphate ions which include phosphorus atoms.

  On the side of life, we have nucleoprotein, the molecules of which consist of a large number of hydrogen atoms, a considerable number of carbon and oxygen atoms, a sizable number of nitrogen atoms and a small number of sulfur atoms. Also a small number of phosphorus atoms.

  If we just look at the kind of atoms in non-life and in life, or even at the relative proportions of the kinds present in both cases, there isn’t much difference. But when it comes to the relationship among the atoms—

  On the non-life side we have small molecules made up, at the most, of five atoms apiece. On the life side we have tremendous nucleoprotein molecules made up of millions of atoms, each placed just so.

  The question is, how did the atoms in these small molecules manage to place themselves just so in order that the first nucleoprotein molecule might be formed? Once one nucleoprotein molecule exists, it can guide the formation of others. But how was the first one formed?

  Could it have been the result of the blind workings of chance? Could the atoms have just happened to bump one another and stuck together in the right pattern—just by chance, after a billion years of random trying?

  To test the blind-chance hypothesis, let’s set up the simplest possible analogy. Suppose we had marbles of six different colors and suppose we took a few million assorted marbles and threw them helter-skelter into a box. Suppose each marble were coated with a kind of cement which would make it stick firmly to any other marble it happened to touch. Having thrown them into the box, pull the whole sticking-together mess out. What are the chances that, just by luck, just by the blind workings of chance, all the colored marbles have so arranged themselves that a pattern equivalent to that of a perfect nucleoprotein is the result?

  Having read Chapter Three, you may be able to make a shrewd guess as to what the answer to that one is. For those of you who have not, I will only say that the chances are more infinitesimal than you or I can imagine. So infinitesimal that, if the known universe were crammed with nothing but people and each person performed the test twenty times a second (a hundred times a second, a thousand times, what’s the difference!) for a billion years (or a trillion or a trillion trillion), the chances of any one of those humans coming up with a perfect nucleoprotein pattern at any instant in all that time is still infinitesimal.

  This kind of thing was pointed out, rather triumphantly, by Lecomte du Noüy in a book named Human Destiny, published in 1947. His point of view was that this proved it to be completely unreasonable to suppose that life had originated by the blind workings of chance and that therefore there must have been some directing intelligence behind its origin.

  The de Noüy argument had quite a vogue (and still has) among people who approved the conclusion and were willing to overlook flaws in the line of reasoning for the sake of that conclusion. But, alas, the flaws are there and the argument contains a demonstrable fallacy.

  Let’s take a simpler case and see if we can spot the fallacy.

  Suppose we start with a mixture of the gases, oxygen and hydrogen. By heating them, we can cause the molecules of oxygen and hydrogen to combine with one another with explosive eagerness. The result is a substance made up of molecules consisting of both hydrogen and oxygen atoms, three atoms altogether, arranged in a V-shape.

  So far, all this is true, but suppose that all this is all you know. Nothing else! What, then, if you start working out what the final molecule might be on the basis of the blind workings of chance? You know that the final molecule contains three atoms, including both hydrogen and oxygen. There are six kinds of combinations that fulfil that condition. Those are:

  H-H-O is equivalent to O-H-H (just turn one molecule around and you have the other) and O-O-H is equivalent to H-O-O. Each can be formed in two different ways, you see, so H-H-O and O-O-H are both twice as probable as are either H-O-H or O-H-O, each of which can be formed in only one way.