Some sponges make skeletons and defensive structures of silica. Hierarchically assembled macrostructure (the skeleton of a deep-sea sponge) appears to be woven of fiberglass.  This remarkably lightweight, crush-resistant architecture is the result of a genetically encoded, protein-mediated synthesis, in which individual cells produce small subunits that are precisely positioned by the cells and then cemented in place. But how is the glass made by living cells, at low temperature and without caustic chemicals, under conditions very different from geological or anthropogenic synthesis?

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