The Right Stuff in the Right Combinations

Will the right sort of planet revolving at the right sort of distance around the right sort of star produce life? The answer seems to be: yes, if it has the right sort of material to work with. Everything to date points to the conclusion that the right materials are automatically there. It is a conclusion practically without debate.

We have a convincing concept for the general formation of the elements (everything heavier than hydrogen and helium). They are formed ubiquitously in the galaxy in the cores and the death throes of stars. The larger stars disperse these elements to space in similar ratios wherever they destroy themselves in their titanic explosions. We have measured the composition of the resultant molecular clouds by spectroscopy. It is a pleasing revelation to find that the composition of the galaxy at large matches that of our solar system. The crucial fact seems assured: the elemental stuff that allowed planets, Earth, and life in our solar system was, and is, available everywhere else in the disk, once the galaxy sent through its initial element-building and dispersing stage s1Fowler 1984 s2Wood & Chang 1985.

We find, then, that the proper elements exist ready for further formation, and these elementals are already combining to form useful molecules. Some of these molecules are chemically active organics which could lead to biology. Especially creative scientists have even imagined life itself being pieced together in space on dust grains or cometary particles s3Hoyle & Wickramasinghe 1980. Whatever the truth of that, it is almost a certainty that the chemistry-of-space produces important biological molecules such as amino acids, the monomeric units of proteins s4Ferris 1984 s5Greenberg 1984. Such substances and others of importance have been found in carbonaceous chondrite meteorites s6Engel & Nagy 1985 s7Irvine 1987.

Around 4 billion years ago, showers of comets and meteorites may have carried the basic compounds of life to Earth. During their encounters with Halley's Comet, the Vega and Giotto spacecraft detected many of the elements necessary for life. Analyses of meteorites and cometary dust that have fallen to Earth have shown us that these interplanetary objects are often rich in organic material s8William Irvine, University of Massachusetts.

These discoveries are important in that they add three almost certain pieces to our vision of the formative days of planetary systems and earthlike worlds:

1. chemical reactions between the elements are so programmed that massive quantities of organic chemicals are made in space and exist in the heavy molecular clouds from which planetary systems form;
2. much of this organic substance condenses into chondritic dust and lumps which form the basis for early planetary cores, contributing ready-made organic chemicals to the neonatal planets;
3. even after planet formation, more lumps and dust (a carbonaceous meteoric rain) continue to fall into the new environments of the "earths," seeding them with potentially biogenic compounds.

This should be happening, and did happen in the past, all over the galaxy: billions of earths soaking up a prebiological rain. The right stuff is present at the right time. Is this enough to ensure life?

When our chemists began to simulate the primordial atmosphere and energy conditions, they were delighted to discover that these original circumstances spontaneously began creating the chemical for life. For two decades the advances have been continual and positive s9Calvin 1975 s10Dickerson 1978 s11Hartman & al. 1985. The primitive conditions not only produce the right biochemicals but they seem to do so in a non-random way. Chemistry's products are determined, and not just anything is possible. Certain atomic arrangements (for example, just certain amino acids or nucleic acid bases) are strongly favored over other arrangements in the same biochemical classes of compounds. There seems to be a limited set of biochemical units out of which earthlike life, and presumably all galactic life, can be constructed.

The linking together, or polymerization, of these small units into the vital structures of proteins or nucleic acids is currently impossible to imitate in our labs in short time frames. Nevertheless, three lines of reasoning lead us confidently to suspect that such polymerization occurs on orderly, rapid and probably uniform fashions on Earthlike worlds:

1. Several polymerization mechanisms have been researched and a few seem to work. They involve high-energy sources (e.g., UV-radiation, lightning, volcanic heat) and high-surface-areas for encouraging catalysis (such as on the bubbles of sea-foam or in the matrices of clay materials). All of these conditions should be available galaxy-wide. Related work, such as the melting of pure biochemical monomers together, and analyzing the resultant products, again shows that not just anything is possible. These melts yield a surprisingly limited variety of polymers.
2. A second line of reasoning involves attempts to calculate the most stable aggregation of molecules, the molecular alliance which would have the best chance to persist in primitive planetary environments. The winners seem to be those aggregates which ally proteins and nucleic acid polymers, the same crucial alliance which lies universally at the basis of Earth's life s12Eigen & al. 1981 s13Schuster 1984.
3. The third line of reasoning is a deduction from a single observation. Whatever route the biochemicals took to form polymers and beyond to simple life, it was not difficult and it happened very rapidly. Life appeared in its simplest forms almost as soon as the Earth has cooled and settled enough to permit it s14Groves & al. 1982 s15Ferris 1987 s16Gould 1978.

On Earth, life began almost as soon as the planet was cool enough to form seas. It is typical, there may be as many as 10 billion Earth-like planets in our Milky Way alone. Today we contemplate a universe teeming with life, some of which may be intelligent s17Bernard Oliver, chief, NASA SETI program, 1987.

More pieces of the prebiological puzzle continue to come to light. The discovery of microspheres, bilayered spherules which spontaneously form from certain proteins, is another important example. These structures behave much like cell membranes, creating differential electric charges on their surfaces and showing division behaviors uncannily like living units. Work with these microspheres and other simple pre-biological systems has inspired their discoverer, Sidney Fox (1984), to say: The experiments suggest that evolution of molecular complexity was capable of occuring from simple beginnings very rapidly... in days or less s18quoted in Ridpath 1975.

Such optimisms about life formation abound in the cosmochemical and protobiological literature. The trend of the work to date supports such optimism. Given the right stuff in the right places (a situation which is the expected galactic norm), life will spontaneously and rapidly form. Returning to the Drake Equation, the factor "f_l" is "1"; life does it everytime, and quickly. It is the basic biochemistry of the universe.

The elements required for life?carbon, nitrogen, hydrogen, oxygen, phosphorus, and sulfur?originate in the formation of stars. Then they evolve into larger organic (carbon-based) molecules in space between the stars. In primitive planetary environments they combine into the building blocks of life, evolve into enzymes and the genetic code, organize into complex and stable cell-like strutures, develop self-replication processes, and grow from simple to complex living things s19Donald DeVincenzi, NASA Ames Research Center, 1987.