Carbon is unique in its ability to combine with other atoms, forming a vast and unparalleled number of compounds in combination with hydrogen, oxygen, and nitrogen. This universe of organic chemistry— with its huge diversity of chemical and physical properties—is precisely what is needed for the assembling of complex chemical systems. Furthermore, the general ‘metastability’ of carbon bonds and the consequent relative ease with which they can be assembled and rearranged by living systems contributes greatly to the fitness of carbon chemistry for biochemical life. No other atom is nearly as fit as carbon for the formation of complex biochemistry. Today, one century later, no one doubts these claims. Indeed the peerless fitness of the carbon atom to build chemical complexity and to partake in biochemistry has been affirmed by a host of researchers. 2
One widely publicized coincidence is the ‘lucky’ fact that the nuclear resonances of the isotopes 12C and 16O are exactly what they need to be if carbon is to be synthesized and accumulate in any quantity in the interior of stars . The energy levels of these resonances ensure that 12C is first synthesized in stellar interiors from collisions between 8Be (beryllium) and He (helium) nuclei and that the carbon synthesized is not depleted later. Hoyle made this discovery in 1953 while working at Caltech with William Fowler. An intriguing aspect of the discovery is that Hoyle made it based on a prediction from the anthropic principle. Hoyle himself
If you wanted to produce carbon and oxygen in roughly equal quantities by stellar nucleosynthesis, these are the two levels you would have to fix, and your fixing would have to be just about where these levels are found to be ... A common sense interpretation of the facts suggests that a superintellect has monkeyed with physics, as well as chemistry and biology and that there are no blind forces worth speaking about in nature.
This discovery was acclaimed not only as a major scientific discovery but also as further evidence of the biocentricity of nature. Hoyle may have been one of the first to notice that the conditions necessary to permit carbon-based life require a very narrow range of basic physical constants, but the idea is now widely accepted. If those constants had been very slightly different, the universe would not have been conducive to the development of matter, astronomical structures, or elemental diversity, and thus the emergence of complex chemical systems.
Fine tuning of carbon
Foundations of Carbon-Based Life Leave Little Room for Error 1
March 13, 2013 |
Life as we know it is based upon the elements of carbon and oxygen. Now a team of physicists, including one from North Carolina State University, is looking at the conditions necessary to the formation of those two elements in the universe. They’ve found that when it comes to supporting life, the universe leaves very little margin for error.
Both carbon and oxygen are produced when helium burns inside of giant red stars. Carbon-12, an essential element we’re all made of, can only form when three alpha particles, or helium-4 nuclei, combine in a very specific way. The key to formation is an excited state of carbon-12 known as the Hoyle state, and it has a very specific energy – measured at 379 keV (or 379,000 electron volts) above the energy of three alpha particles. Oxygen is produced by the combination of another alpha particle and carbon.
NC State physicist Dean Lee and German colleagues Evgeny Epelbaum, Hermann Krebs, Timo Laehde and Ulf-G. Meissner had previously confirmed the existence and structure of the Hoyle state with a numerical lattice that allowed the researchers to simulate how protons and neutrons interact. These protons and neutrons are made up of elementary particles called quarks. The light quark mass is one of the fundamental parameters of nature, and this mass affects particles’ energies.
In new lattice calculations done at the Juelich Supercomputer Centre the physicists found that just a slight variation in the light quark mass will change the energy of the Hoyle state, and this in turn would affect the production of carbon and oxygen in such a way that life as we know it wouldn’t exist.
“The Hoyle state of carbon is key,” Lee says. “If the Hoyle state energy was at 479 keV or more above the three alpha particles, then the amount of carbon produced would be too low for carbon-based life.
“The same holds true for oxygen,” he adds. “If the Hoyle state energy were instead within 279 keV of the three alphas, then there would be plenty of carbon. But the stars would burn their helium into carbon much earlier in their life cycle. As a consequence, the stars would not be hot enough to produce sufficient oxygen for life. In our lattice simulations, we find that more than a 2 or 3 percent change in the light quark mass would lead to problems with the abundance of either carbon or oxygen in the universe.”
There is no physical law to explain it. And neither PHYSICAL NEED. What remains, is chance, or design......
Of the 112 known chemical elements, only carbon possesses a sufficiently complex chemical behaviour to sustain living systems.1 Carbon readily assembles into stable molecules comprised of individual and fused rings and linear and branched chains. It forms single, double, and triple bonds. Carbon also strongly bonds with itself as well as with oxygen, nitrogen, sulfur, and hydrogen. In other words, life molecules must be carbon-based.
At its basic level, however, chemical life must be able to carry the instructions for the construction of its progeny from basic atomic building blocks. These instructions, or “blueprints,” require, among other important things, a complex molecule as the carrier. This molecule must be stable enough to withstand significant chemical and thermal perturbations, but not so stable that it won’t react with other molecules at low temperatures. In other words, it must be metastable. Also, to allow for diverse chemistry, it must have an affinity for many other kinds of atoms comparable with the affinity it has for itself. Carbon excels in this regard, but silicon falls far short. Other elements aren’t even in the race. There are other arguments in favour of carbon, such as the fact that it forms gases when combined with oxygen (to make carbon dioxide) or hydrogen (to make methane), and both gases allow free exchange with the atmosphere and oceans. And most important, when other key atoms— hydrogen, nitrogen, oxygen, and phosphorus—are added to carbon, we get the informational backbones (DNA and RNA), and the building blocks (the amino acids and proteins) of life. Carbon gives these molecules an information-storage capacity vastly exceeding that of hypothetical alternatives. In fact, the half-dozen or so key chemical requirements for life discussed in the literature are rare or absent in other elements but are all present in carbon. (And in case you think there’s a loophole, it doesn’t work to try to create a carbon equivalent by combining several kinds of atoms.) 3
[The entire biological] process depends upon the unusual chemistry of carbon, which allows it to bond to itself, as well as other elements, creating highly complex molecules that are stable over prevailing terrestrial temperatures, and are capable of conveying genetic information (especially DNA). ... Whereas it might be argued that nature creates its own fine-tuning, this can only be done if the primordial constituents of the universe are such that an biological process can be initiated. The unique chemistry of carbon is the ultimate foundation of the capacity of nature to tune itself.
3. Gonzalez, Privileged Planet, page 33
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