carbon (interactive periodic table)
< <
> © David Darling <
> <
> <
> <
> <
> <
| FRONT PAGE | NEWS | ARCHIVE | NEWSLETTER | FORUM | LINKS | ME | THIS SITE | E-MAIL |
The fourth most common element in the universe (see elements,
cosmic abundance) and the basis of all terrestrial life (see elements,
biological abundance). It exists in a number of distinct forms, including
graphite and diamond. Carbon is manufactured
inside the core of evolved stars by a process that involves either a remarkable
coincidence or a piece of cosmic tuning. In this process, two helium nuclei come
together to make a nucleus of beryllium, which then has to capture a further helium
nucleus to complete the synthesis of carbon. However, when the astrophysicist
Fred Hoyle first looked closely at this reaction
in the 1950s he realized there was a problem. According to what was then known,
the capture of a helium nucleus by a beryllium nucleus was far too improbable
to account for the observed cosmic abundance of carbon. He reasoned that the only
way enough carbon could be made was if there existed a very specific match of
nuclear energy levels, or resonance, between helium, beryllium, and carbon under
precisely the conditions thought to prevail in the cores of stars at this stage
in their evolution. Experiments promptly confirmed Hoyle's deduction—there
was indeed a previously unsuspected resonance, very close to the energy value
he gave. Crucially, for carbon-based life-forms, there is not a similar resonance
at the same energy between carbon, helium, and oxygen. If there were, a large
part of the carbon inside stars would quickly be changed into oxygen, and life
as we know it would be impossible. These happy coincidences are cited by those
who argue in favor of the anthropic principle,
although Hoyle himself has put forward a more extreme interpretation:
If you wanted to produce carbon and oxygen in roughly equal quantities by stellar nucleosynthesis, these are the two basic levels you would have to fix, and your fixing would have to be just about where these levels are actually found to be. . . . A commonsense interpretation of the facts suggests that a superintellect has monkeyed with physics . . . and that there are no blind forces worth speaking about in nature.Given the unique ease with which carbon forms long, complex chains and rings, it is difficult (though not impossible) to imagine life with a different chemical basis such as silicon
| Atomic number | 6 |
| Density (water=1) | 2.25 (graphite), 3.52 (diamond) |
| M.Pt. | 3.550C |
| B.Pt. | 4,289C | External site