Pearl Beauty and Design

We have often reported on how design in nature has helped human “inventors” develop new products or improve old ones. It seems that lowly mollusks can teach humans some lessons from pearl beauty and design.

When a grain of sand or a tiny bit of debris enters the mollusk’s shell, such as an oyster or mussel, the creature goes into a defensive action to protect itself from the irritating particle. The oyster deposits a crystalline form of calcium carbonate known as aragonite. Limestone is primarily calcium carbonate, but it lacks the iridescent appearance of this crystallized form. The smooth layers of mineral and protein which the mollusk deposits on the foreign particle is 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. However, pearl beauty and design remained a mystery until recently when a research team studied pearls from Akoya pearl oysters (Pinctada imbricata fucata) in Australia. First, they used a diamond wire saw to slice pearls in half. Then they polished the cut surfaces and used various electron microscopes to study them more carefully than anyone had done before.

The researchers refer to the layers of nacre as “tablets.” For example, one pearl they studied had 2,615 tablets deposited over 548 days, or 4 to 5 tablets per day. The pearl was only 2.5 mm in diameter, so the tablets were extremely thin. However, 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 some math to adjust the thickness of the layers to compensate for irregularities. Where one layer is thin, the next is thicker to self-correct, so irregularities heal themselves in the following few layers.

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 materials from which they make it. Another research team member, Robert Hovden, a materials scientist and engineer at the University of Michigan, said that understanding how mollusks make pearls could inspire “the next generation of super materials.” That might include materials for better solar panels or for use in spacecraft.

Once again, design in nature gives us some valuable insights. Even lowly mollusks can teach humans some lessons through pearl beauty and design, thanks to the Designer of nature.

— Roland Earnst © 2021

References: ScienceNews.org, and Proceedings of the National Academy of Sciences