Carbon monoxide has one carbon atom and one oxygen atom, and chemists file it under inorganic. Stick a hydrogen onto it and you get HCO, which is probably organic by now. Methane, CH4, is organic without argument. Between a molecule that doesn't count and one that does, there is sometimes a single atom.
That is how Dmitry Wiebe sees the line. He is an astronomer, a Doctor of Physical and Mathematical Sciences at the Institute of Astronomy of the Russian Academy of Sciences, and he studies the chemistry of interstellar matter. His rule of thumb is short. Carbon must be there, most likely bonded to hydrogen. Oxygen, nitrogen and anything else may come along. Look through different sources, he says, and you may not even find one agreed definition.
The word has a pull, though. "Organic matter found on Mars" sounds like the first line of a story about Martians. Wiebe's answer is flat: the word has no direct connection to life. It describes the structure and composition of a molecule, nothing more. He admits there is "a certain magic of the word" at work. Organics are plentiful in the universe: on the surface of Mars, and, he adds, never mind comets and asteroids. So the next time a headline announces organic compounds somewhere far away, you can read it as "carbon compounds found", which is a much less dramatic sentence.
So why does the label exist? Because it once meant something. In the late eighteenth and early nineteenth centuries chemists already understood that life runs on chemistry, but nobody knew how that chemistry got started. Berzelius, Wiebe thinks, was the one who split the subject in two. Inorganic chemistry was the chemistry of the nonliving. Organic chemistry was the chemistry of organisms, endowed with a special vital force that made biological activity possible.
The vital force did not survive the century. Again and again, chemists made organic compounds from inorganic ingredients. Friedrich Wöhler's urea in 1828 is the famous case. The wall had no door in it after all.
There is actually no difference between organic and inorganic chemistry, but this division has remained, it is, in general, purely historical, because there are no fundamental differences, as we now understand, between a CO molecule and a CH4 molecule.
на самом деле никакой разницы между органической и неорганической химией нет, но это разделение осталось, оно, в общем, чисто историческое, потому что никаких принципиальных отличий, как мы теперь понимаем, между молекулой СО и молекулой CH4 нет.
— Dmitry Wiebe, Think Like a Scientist, 39:38
The old wall can even be crossed on Mars. In May 2024 Yuichiro Ueno and colleagues reported in Nature Geoscience that organic matter in ancient Martian sediments, with a depleted isotopic makeup, could have been built from carbon monoxide. Sunlight would have made that gas by splitting carbon dioxide in the early Martian atmosphere. It is the very molecule that Wiebe's list puts on the "inorganic" side.
Something does set carbon apart, and Wiebe is quick to say so. Carbon can produce a colossal number of molecules, from the very simple to the very complicated. That is the real subject of the division, and it is why he finds a plainer name more honest: the chemistry of carbon. The split between organic and inorganic, he says, is a matter of method and wording. It is not fundamental, and it is not scientific.
The odd result is that the scientists' own vocabulary does some of the misleading. A word coined to mark where life's chemistry begins now lives on as a name for any carbon compound. Carbon monoxide, sitting just outside it, is among the raw stock.
