36 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”In 2011, Callahan and coworkers investigated the abundance of
nucleobases of 12 different meteorites, including the Murchison, and
detected adenine and guanine, along with their analogs. The distribu-
tion of nucleobases is similar to what was produced in the laboratory
by reacting hydrogen cyanide, suggesting a mechanism for the origin of
these extraterrestrial compounds.^16
Comets are small, icy bodies that orbit around the sun with certain
periodicities. The Comet “Wild 2” is believed to have formed at the high
temperature region near the newly formed sun, and may have included
particles from interstellar space long before our solar system existed. In
2006, NASA’s spacecraft called Stardust was sent to snatch a sample of
the comet and return it to Earth. Aside from inorganic materials, a host of
organic molecules, believed to have been preserved for 4. 5 billion years,
was found. Mission scientists detected polycyclic aromatic hydrocarbons
(PAH) and numerous nitrogen- and oxygen-rich compounds, including
traces of glycine and beta-alanine (the latter not a protein component).^17
Some organic compounds found in comets are listed in Table 3.6.
Cosmic dust consists of tiny particles, ranging from a few molecules
to aggregates of 0.01 mm in size, floating ubiquitously in space, frequently
Table 3.6. Some Organic Compounds
in Comets
Name Formula
Methanol CH 3 OH
Formamide HCONH 2
Methane CH 4
Ethylene C 2 H 4
Methylacetylene CH 3 C 2 H
Formic acid HCOOH
Acetonitrile CH 3 CN
Methyl formate HCOOCH 3
Acetylene C 2 H 2
Ethane C 2 H 6
Hydrogen cyanide HCN
[See Note 25; permission Royal Soc.]