At the microscopic level, blocks of calcium carbonate crystals in conch shells can dissolve away in more acidic conditions caused by high carbon dioxide (CO2). The conch on the right, reared under CO2 levels in today's atmosphere, produced a shell with orderly blocks of crystals, while the conch on the left, grown under 2,850 ppm CO2 conditions, produced irregular, disordered blocks with etched surfaces. (Micrograph by Justin Ries, Woods Hole Oceanographic Institution)[back]
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