NASA-funded researchers have identified traces of vitamin B3 have been in carbon-rich meteorites, supporting a theory that the origin of life may have been assisted by a supply of key molecules created in space and brought to Earth by comet and meteor impacts.
"Vitamin B3, also called nicotinic acid or niacin, is a precursor to NAD (nicotinamide adenine dinucleotide), which is essential to metabolism and likely very ancient in origin," said Karen Smith of Pennsylvania State University in University Park, Pa. Smith is lead author of a paper on this research, along with co-authors from NASA's Goddard Space Flight Center in Greenbelt, Md., now available online in the journal Geochimica et Cosmochimica Acta.
"It is always difficult to put a value on the connection between meteorites and the origin of life; for example, earlier work has shown that vitamin B3 could have been produced non-biologically on ancient Earth, but it's possible that an added source of vitamin B3 could have been helpful," she added.
Vitamin B3 was first found in meteorites in 2001 by a team led by Sandra Pizzarello of Arizona State University. In the new work, Smith and her team found vitamin B3 at levels ranging from about 30 to 600 parts-per-billion in eight different carbon-rich meteorites, called ‘CM-2 type carbonaceous chondrites’. They also found other pyridine carboxylic acids at similar concentrations and, for the first time, found pyridine dicarboxylic acids.
"We discovered a pattern,” she said, “less vitamin B3 (and other pyridine carboxylic acids) was found in meteorites that came from asteroids that were more altered by liquid water. One possibility may be that these molecules were destroyed during the prolonged contact with liquid water."
"We also performed preliminary laboratory experiments simulating conditions in interstellar space and showed that the synthesis of vitamin B3 and other pyridine carboxylic acids might be possible on ice grains."
B3 not from ET
The team doubts the vitamin B3 and other molecules found in their meteorites came from terrestrial life for two reasons. First, the vitamin B3 was found along with its structural isomers – related molecules that have the same chemical formula but whose atoms are attached in a different order. These other molecules aren't used by life. Non-biological chemistry tends to produce a wide variety of molecules -- basically everything permitted by the materials and conditions present -- but life makes only the molecules it needs. If contamination from terrestrial life was the source of the vitamin B3 in the meteorites, then only the vitamin should have been found, not the other, related molecules.
Second, the amount of vitamin B3 found was related to how much the parent asteroids had been altered by water. This correlation with conditions on the asteroids would be unlikely if the vitamin came from contamination on Earth.