An exotic class of inorganic crystal aggregates known as silica biomorphs earns its name from a remarkable resemblance to primitive organisms. Indeed, five years ago Juan Manuel García-Ruiz of Spain’s University of Granada, Stephen Hyde of the Australian National University, and their colleagues published a study documenting the near indistinguishability between a variety of biomorph structures and certain Australian bacterial microfossils. 1 A cautionary tale, the paper confirmed that simple inorganic chemistry can give rise to the complex, curved shapes and structures once thought restricted to biological materials. The moral: Scientists who date Earth’s earliest life forms cannot rely on morphology alone to determine what qualifies as biogenic.

Despite its complex shape, a silica biomorph is exceedingly easy to make. The material self assembles when barium chloride (or some other water-soluble alkaline-earth salt) is mixed with a silica-rich solution at ambient pressures and temperatures and at high pH. Carbon dioxide...

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