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Secrets in the Shell



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Abstract:

Figure%201.%20House%20decorated%20with%20conch%20shellsClick to Enlarge ImageThe queen conch is a marine snail that grazes seagrass beds in shallow Caribbean waters. It does so openly, and with little fear of natural predators: Unmolested by human fishers, an adult conch may live 20 years. This prodigious lifespan for an invertebrate is possible because of the conch's amazing shell, a defensive adaptation that represents the pinnacle of molluskan evolution. In conch shell, slender crystallites of calcium carbonate are bound by a proteinaceous glue into planks, sheets, and layers, and at each level of organization, adjacent elements are oriented at right angles. This architecture dissipates the force that might otherwise fracture the shell through a system of noncatastrophic microcracks. Breaking into a conch shell requires a crack to travel a tortuous path of false starts and switchbacks as it wends from sheet to sheet and layer to layer. In addition to such estimable toughness, the shell microstructure self-assembles and is self-healing, providing a lofty target that human engineers are beginning to match.


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