Vitamin B3 delivered to Earth by meteorites
Ancient Earth might have had an extraterrestrial supply of vitamin B3 delivered by carbon-rich meteorites, according to a new analysis.
The findings support 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.
"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," said Karen Smith of Pennsylvania State University.
"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 Smith, lead author of the study, along with co-authors from NASA's Goddard Space Flight Center in Greenbelt.
This is not the first time vitamin B3 has been found in meteorites. In 2001 a team led by researchers from Arizona State University discovered it along with related molecules called pyridine carboxylic acids in the Tagish Lake meteorite.
In the new work at Goddard's Astrobiology Analytical Laboratory, Smith and her team analysed samples from eight different carbon-rich meteorites, called "CM-2 type carbonaceous chondrites" and found vitamin B3 at levels ranging from about 30 to 600 parts-per-billion.
They also found other pyridine carboxylic acids at similar concentrations and, for the first time, found pyridine dicarboxylic acids.
"We discovered a pattern - 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," said Smith.
"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," Smith said.
The team doubts the vitamin B3 and other molecules found in the 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 produces 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.
The study was published in the journal Geochimica et Cosmochimica Acta.
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