In its impure forms, silicon (Si) is the eighth most common element in the universe by mass and makes up more than a quarter of the Earth’s crust by mass; it is the second most abundant chemical element on Earth after oxygen. Our earliest human ancestors used silica flints for tools and this startling element remains to date among the most expedient to humankind. Silicon compounds are used extensively in the making of alloys, dynamo and transformer plates, cosmetics and hair conditioners, solar cells, waterproof sealants, and, perhaps most famously, semiconductors, which are key in the computer and microelectronics industries. When William Shockley, the creator of the transistor, moved from New Jersey to Mountain View, California, in 1956, very few people would have anticipated the surrounding area would soon be named after the unassuming and ubiquitous element.

Silicon and carbon, both abundant throughout the universe, are chemical kin. Two nonmetals, they are neighbours in the fourteenth series of the periodic table of chemical elements. They react and behave in similar ways, and many of the compounds created using carbon or silicon are almost identical. But silicon and carbon have major differences too. While silicon is inorganic, carbon is elemental of all known organic life-forms and plays a vital role in the metabolic processes of all of these life-forms; they use carbon compounds for their metabolic and structural functions, to define and control their genetic code and form. If carbon is the element of biotic life, now widely understood as “a metric of the human” (Whitington 2016), silicon is perhaps the element of machinic life; the metric of the robotic, it is the building block of information processing systems.

The boundary between life and nonlife, the organic and the inorganic, has become increasingly difficult to draw. This blurring of boundaries reached new levels in 2010, when geneticist Craig Venter created the first synthetic life-form by building the genome of a bacterium from scratch and coating its DNA with watermarks to trace its descendants. But this blurring of the biotic and abiotic also finds precedent in the existence of self-reproducing organisms such as viruses. There are remarkable parallels between biological and computer viruses in terms of how they self-replicate. Elizabeth A. Grosz (1998, 45) asks, does it matter whether viruses “are enacted in carbon or silicon-based form. . . whether its content is chemical or informational?” For Grosz, viruses of “both biological and silicon form” (45) are linked by their programming logic.

In recent years, biologists have renovated their understandings of the origin of the four major biological domains of life—viruses, bacteria, archaea, and eukarya—from which all microbes, fungi, plants, and animals are derived. These discoveries have renewed speculation on how alternative ways of life might arise on other planets and moons, and how chemically different such life might be. If life is ultimately always a “biochemical becoming,” as Hannah Landecker (2018) has suggested, where beings and entities are never fixed but rather in constant processes of change, perhaps then silicon is a valuable trope to further trouble humanist binaries and dogmas. With silicon, we can speculate about alternative biochemistries of life—say, in alien extraterrestrial worlds—which could have a different chemical baseline for life.

Life itself has morphed as living things are rearranged, simulated, and tampered with, "destabiliz[ing] any naturalistic or ontological foundation that life forms" (Helmreich 2011, 673). A definition of life that could guide the search for life outside Earth is also still very rudimentary. Life forms with alternative biochemistries might not necessarily have observable properties that could distinguish them from inanimate matter. A big gap still exists within the life sciences attempts to come up with a theory of life that might involve other classes of carbon compounds, compounds of another element (such as silicon), or other solvents instead of water (such as ammonia or methane).

Popular science fiction and cosmology alike have speculated about the potentialities of silicon-based life. In 1894, H. G. Wells wrote about his visions of silicon-aluminium organisms on other planets, wandering through atmospheres of gaseous sulphur and the shores of a sea of liquid iron. In formulating this alternative chemical cosmology, perhaps Wells was not aware of diatoms, first categorized by Danish naturalist Otto Friedrich Müller in 1783, a class of Earth-bound and carbon-based photosynthesizing algae distinguished by having cellular walls composed of hydrated silicon dioxide. Diatoms are found in oceans, waterways, and soils everywhere in the world and are thought to generate 20 percent of the oxygen produced on the planet each year, taking in over 6.7 billion metric tons of silicon each year from the moisture in which they live. Diatoms contribute in significant ways to the modern oceanic silicon cycle, as they are the source of most biological production.

In fact, diatoms are not alone in their silicon liveliness. For example, in 2006, researchers at University of Padua coupled together living brain cells and silicon circuits for the first time, opening new avenues for neurological bioengineering. Experimenting with what has been termed directed evolution, synthetic biologists at CalTech have used microbes to create novel molecules where enzymes generate organo-silicon compounds (Kan 2016). These mutant enzymes can self-generate these compounds, leading to speculation about the possibilities of organosilicon-based life as life-forms might be induced (and seduced) into incorporating silicon into their basic components.

Artificially made silicon compounds and neurological silicon circuits suggest a broader set of truths about their elementality. Silicon is entwined in the precariously stable life processes of humans today and tomorrow. Independent of the chance that silicon-based life-forms could exist on other planets, humans are already chemically bound up with silicon. We are silicon life and life-forms.