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The Star Larvae Hypothesis
Nature's Plan for Humankind
Part 2. Star Larvae

Silicon and Biogenesis

Atoms are star spores. Biological life is cosmic, not terrestrial, in origin and scope.

Accounting for the origin of biological life remains a conundrum. Assertions fly. And scientists, theologians, and school boards are likely to continue their disputations for some time.

Whatever the merits of the various arguments, this much is certain: If the universe spent its first moments as a dense ball of radiation, as most scientists believe, then it could not have harbored biological life from the beginning. The first biological cells arose at some time and at some place during the subsequent development of the universe.

According to the standard cosmogony, the Big Bang's primordial radiation cooled as it expanded, and from the cooling a supply of subatomic particles condensed. This original supply of particles, under the influence of gravity, organized itself into diffuse bodies, or clouds, at various places in the developing universe. As each cloud grew more massive, it condensed at an accelerating rate, under the pull of its own gravity. Eventually, pressures in the dense centers of these clouds ignited nuclear reactions, and the first generation of stars was born. These original stars manufactured, as each generation continues to do, the various species of atoms that are needed to construct planets, moons, comets, and the other components of solar systems. Nature uses an assortment of atoms in her manufacturing processes: ordinary metals; radioactive metals; inert gasses; and the biologically important elements carbon, nitrogen, and oxygen.

Once the universe became stocked with an inventory of atomic widgets, these components became organized into simple molecules, complex organic macromolecules, and ultimately into viruses and bacterial cells. Where and how did this precise engineering occur?

The prevailing scientific assumption is that the organization of atoms and simple molecules into macromolecules and cells occurred somewhere on the surface of the early Earth. Attempts to recreate the chemical, thermal, and other physical conditions that predominated on Earth after it cooled from its initially molten state have been made in various laboratory experiments. The pursuit of the chemical path that led to the first cell has left behind a legacy of inconclusive results, in which mixtures of simple molecules, such as methane, ammonia, carbon dioxide, and water, reacting chemically under the influence of electric sparks or other energy sources, have produced various consistencies of organic sludge. The experiments have been modified in various ways, as scientists have tried to produce a promising result. But the process by which living cells arose, or could arise, from nonliving material remains mysterious.

However, the simple observation that material moves through the galaxy—pushed by stellar winds and carried by comets and by the circulatory effects of the galaxy’s own rotation—means that the Earth-centric assumption can be set aside, and investigators can cast their nets almost anywhere in search of conditions favorable to the construction of the first biological cells.

Are there places beyond Earth where conditions are known to exist that could host the processes necessary to assemble atoms and simple molecules into macromolecules and then into complete cells? In industry, the application of manufacturing and assembly methods to the construction of molecular-scale devices is called nanotechnology. The search for the origins of biological life should focus on finding conditions conducive to a natural nanotechnology, a manufacturing infrastructure that could produce amino and nucleic acids and assemble them into viruses and bacteria. In other words, a cell factory. One set of conditions that has many more factors in its favor in this regard than do those on the surface of a freshly minted planet is the set of physical and chemical conditions that occurs inside the cloud of gas and dust from which a star and its planets condense. The energetically dynamic environment of an embryonic solar system seems to be ideally suited for the miraculous production of life. And the element silicon seems naturally cast in the supporting role of midwife.

The relationship between carbon, the central element of biology, and silicon, the central element of electronics, is noteworthy just from the fact that each type of atom has a predilection to bond chemically with its own kind. This habit produces a kind of parallelism on the macroscopic scale of the forms and properties characteristic of these elements. For example, they both form three-dimensional crystals, carbon as diamond and the so-called buckeyballs or fullerenes, and silicon as varieties of familiar mineral crystals, or silicates, including precious stones and clays, along with, under human influence, the circuitry of electronics. Arranged less tightly, the atoms compose flexible chains, such as those that form the "backbones" of plastic polymers (carbon) and synthetic rubbers, or silicones (silicon). These two elements are unique in their tendency to bond chemically to form matrices and chains, and this shared affinity might predispose them to work cooperatively under the right conditions.

A natural nanotechnology, or cell factory, needs an energy source. And it needs a means of directing chemical energies precisely to shepherd chemical reactions up against the thermodynamic gradient through levels of increasing chemical complexity, further and further from chemical equilibrium. It has to be able to catalyze organic reactions and provide some sort of physical structure that could hold organic molecules steadily in place during their assembly into the macromolecular components of a cell.

Given these criteria, silicon tops the list of potential midwives for the organic synthesis that gives birth to living cells. Silicon naturally, in conjunction with various metals, forms a variety of periodic and aperiodic crystalline forms potentially capable of serving as geometric templates for organic components during various phases of assembly into macromolecules. Nucleic acids and proteins in their crystalline forms could handily interlock with silicate crystals in secure arrangements during their assembly into larger structures. (Crystallography remains a primary laboratory technique for determining the structures of proteins. It is the methodology that was used to determine the double helix structure of DNA.)

Silicon also has photoelectric properties; that is, it can convert light into electricity. The solar-energy industry exploits this photovoltaic ability. As a result, silicon potentially solves the problem of energy conversion into a form that could be used to control organic synthesis precisely at a molecular level. Such capabilities would be of immense practical use in the service of a cell factory.

Silicates also have a capacity to catalyze organic synthesis—certain chemical reactions that build complex organic molecules from simpler ones occur more readily in the presence of certain silicate minerals. Clay-catalyzed RNA synthesis, for example, has been demonstrated in the research of James Ferris at New York’s Rensselaer Polytechnic Institute (see http://www.origins.rpi.edu/chem_pubs.html#ferris). NASA researchers Hugh Hill and Joseph Nuth similarly have demonstrated the ability of amorphous iron and magnesium silicates to catalyze a variety of organic molecules from a gas mixture containing only carbon monoxide, nitrogen and hydrogen.

As to where a silicate-managed nanotechnology might operate in nature, it turns out that all of the necessary ingredients are at hand in what astronomers call "the local interstellar cloud," which is the cloud of gas and dust particles in which our solar system is embedded. The most abundant element there, as throughout the universe, is hydrogen, the starting material from which all other elements are manufactured. Next in abundance in the local interstellar cloud are the elements carbon, oxygen, and nitrogen, the primary building blocks of organic chemistry—and silicon, magnesium, and iron, potentially suitable building blocks for a natural nanotechnology for the manufacturing of biological cells.

Hill and Nuth, from observations of young stars of intermediate size, so-called Herbig Ae stars, which resemble our own sun in its infancy, and from observations of the known content of comets, propose that in the early stages of solar-system formation amorphous silicate grains catalyze simple organic reactions to produce a variety of prebiotic organic molecules. These reactions require the heat and pressures found near the protostar, but the grains, coated with their organic produce, then are transported by a "circulatory system" of material flowing from the center of the nebula out to a distance typical of that at which comets are thought to form. (The research by Nuth, Hill, and colleagues appears in Lunar and Planetary Science XXXIIII [2002], and see the paper "Protostars are Nature's Chemical Factories," by Nuth and Johnson in Lunar and Planetary Science XXXVI [2005]. A summary in provided in "Constraints on Nebular Dynamics and Chemistry Based on Observations of Annealed Magnesium Silicate Grains in Comets and in Disks Surrounding Herbig Ae/Be Stars", Proceedings of the National Academy of Sciences, Vol. 98, No. 5, Feb. 27, 2001, 2182-2187.)

Hence, a mechanism exists by which organic material can become incorporated into comets, and we know that comets are rich in organic material. At later stages in the development of a solar system, when planets are forming, the characteristic silicate material identifiable in the circumstellar dust includes a greater proportion of crystalline (as opposed to amorphous) silicates, and the organic content of the dust comprises increasingly complex molecules. This suggests a two-step process, in which simple organics are catalyzed near the protostar, then transported to cooler regions for further, more precise processing that involves the participation of crystalline silicates.

Because crystallization on Earth is subject to sedimentation and the turbulence of convection currents, the semiconductor industry continues to work with NASA to investigate silicon crystallization in space. In weightlessness silicon crystals can be grown larger and with greater purity—geometrical regularity—than they can on Earth. Darwin's hypothetical "small warm pond" in which he imagined life arose, may be a less appropriate image than that of a "big cold cloud."

Some silicon crystals also possess piezoelectric properties. Under pressure, they generate an electric current. Phonograph needles exploit this effect. Piezoelectric effects provide another potential source of energy for a silicate-enabled cell factory. And, as an overarching observation in support of this scenario, a prominent scientific model of interstellar grains, based on spectrographic analysis, is of carbonate shells covering silicate nuclei.

In summary, the star larvae hypothesis tightens the scientific model of biological origins by proposing

• Specific physical mechanisms: crystalline silicate templates or "scaffolding" to hold in place partially assembled macromolecules during assembly, silicate catalysis of organic chemistry, and a souce of (electrical) energy available to molecular-scale assemblies.
• Specific material agents driving the mechanisms: amorphous and crystalline silicate minerals.
• Specific locations where the agents are observed to comingle with organic material: cooling stellar/planetary nebulae.

Many details remain to be worked out, but this added specificity gives the hypothesis a leg up on standard scientific models.

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