Mike Tettenborn sighed:
Once again my budding scientist son has decided to work with meteorites in
his science fair. I am thrilled at this but I may have to donate a 1.2 gram
sample of Murchison.
Organic Clues in Carbonaceous Meteorites
(April, 1979, Sky Telescope, pp. 330-332)
C.R. Pellegrino and J.A. Stoff, Rockville Centre, New York
On September 28, 1969, an ancient rock mass slammed into the upper atmosphere
somewhere above Australia. It slid, danced, and leaped through the air, then
exploded over the town of Murchison. For several days thereafter residents and
scientists recovered curious shards of grayish matter from fields, roadsides,
and rooftops. The pieces resembled dried carbon-rich clay and crumbled with
similar ease.
Upon closer examination, their matrix appeared to be studded with tiny glasslike
spheres. When these were sectioned and viewed under a microscope, concentric
layers of material, not unlike those distinctive patterns recognized in pearls,
became visible. Further analysis revealed unexpected traces of water (as high as
10 percent by weight) locked inside the stony fragments. The 20th specimen then
known of that most puzzling and sought after of all meteorite types, the
carbonaceous chondrite, had arrived.
Nearly three years later, scientists at NASA's Ames Research Center in
California confirmed the presence of 17 different fatty acids and 18 amino acids
in fragments of the Murchison meteorite. These highly complex substances are
composed of organic elements and, when woven properly together, comprise the
foundations of cellular life. But one very important question soon arose: were
these substances truly indigenous to the meteorite, or did the meteorite, upon
its penetration into our atmosphere, begin to breathe in earthly contaminants?
After all, a mere fingerprint on its surface would have contributed most of the
common amino acids known here on Earth.
During the three-year investigation that followed its arrival, the Murchison
meteorite was examined and compared closely with another carbonaceous chondrite
that had fallen near Murray, Kentucky, 19 years earlier. The results were
impressively similar. Of the 18 amino acids detected in the two meteorites, the
12 most abundant are seldom if ever associated with the living tissues of
terrestrial plants and animals. The remaining six (valine, alanine, glycine,
proline, aspartic acid, and glutamic acid) are prominent in earthly proteins,
but relatively scarce in carbonecous chondrites. The first of a long series of
paradoxes had begun to emerge.
The meteorites may have originated in an age when the dust of the solar nebula
was falling together into little bodies that became celestial vacuum cleaners,
ever increasing in girth as they continued to sweep up debris in their path.
Some, like our own earth, accumulated great mass. Their interiors began to heat
up. Gases, steam, and vaporized rock held fast to their shifting skin: the
primordial atmospheres were born.
Whether the result of a cataclysm involving the collision of ancient worlds or
simply a collection of discarded planetary scraps left hanging about the sun, a
thin belt of solar driftwood - the asteroids -spreads wide between Mars and
Jupiter. It is from this belt that most meteorites seem to originate.
The presence of organized elements and hydrocarbons in some of these meteorites
leaves several unanswered questions. These substances seem to have no business
being out there in the first place. If they are native to the meteorites, then
we are faced with a perplexing fact: these carbon compounds were somehow lifted,
against entropy, to a highly ordered state from vast numbers of random
dissociated, inanimate atoms, and gathered up and arranged in their present
condition of seemingly improbable symmetry. Given only the extreme temperatures,
damaging radiation, and near emptiness of outer space, it is not likely that
this kind of clustering could have proceeded in objects so small as stones,
boulders, or even asteroids (nor that it should be reproduced so agreeably among
individual samples).
Detailed comparisons with earthly tissues seem only to sharpen the contrasts
between terrestrial proteins and the kinds of molecular ornamentation typically
recovered from carbonaceous chondrites. That the history of these compounds
differs from our own is underscored by important eccentricities in their
molecular structure.
It is generally believed by organic chemists that when the earth was still in
its infancy, when its vapors had condensed into newly formed seas and its shroud
of air lacked destructive oxidizing agents, the first organic acids were
probably assembled in two very distinct varieties. Valine, for example, possibly
occurred as mirror images of itself, much in the same way as your right and left
hands are mirror images, or isomers, of each other. In those days before the
dawn of living self-replicating matter, both right-handed and left-handed
molecules might have
