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When a grain of sand or a tiny bit of debris enters a mollusk's shell, such as an oyster or mussel, the creature goes into a defensive action to protect itself from the irritating particle. As a result, the oyster deposits a crystalline form of calcium carbonate known as aragonite. The smooth layers of minerals and protein that the mollusk deposits on the foreign particle are called nacre (pronounced NAY-ker). The layers of nacre take on a beautiful, iridescent, and shiny appearance that gives pearls their beauty.

The question that has bothered scientists for more than a century is how the oyster can change a jagged or lopsided fragment of grit into a perfectly round and smooth pearl. Recently, a research team studied pearls from Akoya pearl oysters (Pinctada imbricata fucata) in Australia. First, they used a diamond wire saw to slice the pearls in half. Then they polished the cut surfaces and used various electron microscopes to study them more carefully than anyone had done before.

One pearl they studied had 2,615 layers of nacre deposited over 548 days. The pearl was only 2.5 mm in diameter, so the layers were extremely thin. They found that the mollusk modulates the thickness of the nacre layers according to “power-law decay across low >to mid frequencies, colloquially called 1/f noise.” That means the mollusk uses math to adjust the thickness of the layers to compensate for irregularities.

One of the researchers, Laura Otter, a biogeochemist at the Australian National University, said: “These humble creatures are making a super light and super tough material so much more easily and better than we do with all our technology.” Using calcium carbonate and protein, oysters make nacre 3,000 times tougher than the raw materials. Understanding how mollusks make pearls could lead to a new generation of super materials for use in spacecraft or solar panels. Once again, design in nature gives us some valuable insights. Thanks to the Designer of nature, even lowly mollusks can teach humans some lessons.

Picture credits:
© New Africa. Image from big stock.com.