Reach out your hand anywhere on Earth's surface and you will probably touch silicon. It sits in the sand, in the gravel, in the wall of every stone house. In the crust we actually walk on, there is more silicon than carbon. So if a writer wants to invent an alien made of something other than us, silicon looks like the obvious candidate. Why did life on Earth never use it?
Dmitry Wiebe, an astronomer at the Institute of Astronomy of the Russian Academy of Sciences who studies the chemistry of interstellar matter, was asked exactly this on "Think Like a Scientist". His answer is short, and it matters for anyone who has watched a film about silicon aliens and wondered whether the idea holds up. It says that when we look for life elsewhere, the question is not what is abundant but what can change.
The case for silicon is real, and Wiebe grants it. Its outer electron shell is built like carbon's, so in principle it can form fairly large molecules. It is common across the Universe, though less common than carbon. And in Earth's crust it wins on numbers.
Then comes the catch. "Silicon is plentiful, but it is part of stone," he says, and making something alive out of stone, under our conditions, looks like a hard job. Silicon on Earth does not float around looking for partners. It sits locked in silicates, the minerals that make up rock.
Silicon is plentiful, but it is part of stone. And making something alive out of stone, under our conditions, seems rather problematic.
Кремния много, но он входит в состав камня. А из камня породить что-то живое в наших условиях кажется достаточно проблематичным.
— Dmitry Wiebe, Think Like a Scientist, 43:45
Silicates are too stable. Carbon, at ordinary temperatures and pressures, builds a huge number of molecules that are not very strong. They can be rearranged, and they allow mutations and changes. Silicon, in his words, "settles into the lattice" and feels perfectly comfortable there. Nothing you do will shift it.
That is the whole argument, and it is a neat one. Life needs material that can be rewritten. A crystal that is happy as it is has no reason to become anything else.
Wiebe is careful about how far this goes. He calls it a limit of our conditions, roughly 20 degrees Celsius and one atmosphere of pressure. Change the temperature or the pressure, or shift the ratio of silicon to magnesium, and the picture might look different. Researchers do work on this, and he thinks it is right to keep the alternative in mind. He does not strike silicon from the periodic table. But he has not heard of anything good coming out of those variations, and no working version of silicon biochemistry is in sight.
He is sharper about fiction. Films about silicon life, he says, offer no real alternative. They say "silicon, basically, somehow" and stop. No chemistry is proposed for what actually happens inside such a creature. Carbon, by contrast, supports a dizzying tangle of chemical processes that we can study. Nothing like it is seen for any other life-building element. He admits this is chauvinism, but a forced one: we work with the only material we have, and that material is carbon-and-water life.
The lab world has not been idle. In a January 2024 paper in Science, Nicholas Sarai and colleagues used directed evolution to engineer a bacterial enzyme, a variant of cytochrome P450 BM3, that breaks silicon–carbon bonds in certain silicon-containing compounds. Life, given a push, can learn to handle silicon bonds. In March 2025 an arXiv paper by Aniruddha Acharya pointed to large amounts of silicon on Mars and the Moon, and to enzymes that can attach silicon to organic molecules, as fuel for the theory of silicon-based life. Both works are about carbon-based chemistry reaching toward silicon, though. Nothing in them replaces carbon.
So the picture Wiebe offers is quieter than the movies. Silicon is not rejected for being rare. It is passed over because it is too good at staying put.
If we ever find something alive on a distant world, the story says, it will probably be made of the same unruly, rearrangeable stuff we are, not of the stone beneath its feet.
