The element germanium lies just below silicon (which is just below carbon) on the Periodic Table, and like both Si and C can form four simultaneous bonds with other atoms. Life is based on complex molecules built around C, and Si-based life has long been a favorite concept in science fiction. Is Ge-based life possible? Germanium-based semiconductors are important components of transistors and other electronics, so Ge-organic molecules could potentially provide a range of electron routing functions in exotic biochemical components. Germanium has a high optical index of refraction, making it useful in fiber optic applications… and potentially in organic signal-transducing macromolecules.
There are a few known Ge-organic molecules, including germane (GeH4), which is a structural analog of methane (CH4). A few other Ge-organic compounds are known, but all are synthetic. Germanium is a fairly rare element, occurring at a concentration of about 1.6 parts per million (ppm) in average crustal rock on Earth. The element could exist at higher concentrations on planets around higher-metallicity stars, but even there Ge would probably never exceed the low ppm range. The rarity of Ge argues strongly against its natural capture into complex chemical processes leading to self-replication, and even if such a thing happened in some anomalously Ge-enriched corner of a distant planet there would be little potential for it to spread further. Carbon-based life requires C, but C is one of the most abundant elements in the universe after hydrogen and helium. There’s plenty of raw material in the universe for our kind of life… but almost certainly not enough for Ge-based organisms to get started, much less to proliferate.
In the cosmologically distant future Ge-based life might be possible. Hundreds of billions of years from now, when the background cosmic abundance of heavy elements is several orders of magnitude higher than now – a time when most stars will rely on fusing C or higher elements to eek out a meager existence because much of the universe’s original H will be used up by then – planets will have a very different basic chemical makeup than they do now. Rocky planets formed under such conditions would be poor in light elements but comparatively rich in heavies… including Ge. Strange chemistry would happen on such worlds, perhaps occasionally strange enough to polymerize Ge into chemically stable complexes capable of capturing energy and using it to build copies of themselves.