July 26 Saturday Science Stumper!



How has this diamond caused scientists to radically revise their diagrams of Earth as a water world?



Nacre is the inner lining of shells that we call “Mother of Pearl.” It’s also the coating that gives pearls their luster. Mollusks secrete nacre to encase pathogens or irritants to protect their own soft tissues. But though nacre (rhymes with acre) exudes a cool, liquid iridescent light, it’s composed of many layers of plates assembled from aragonite. When light hits nacre, some is reflected right off of its surface, but much of it penetrates through the translucent layers of nacre. At each layer, some light penetrates deeper while other light is reflected. Light can even be reflected by in inner surface downward before bouncing outward again. Imagine this happening million and millions of times at any given moment through each 500 nanometer thick layer of nacre. Optical engineers might recognize that this thickness matches the wavelength of human perception, because our eye can detect wavelengths between 390nm-700nm.

Though beutiful to our attuned eyes, nacre’s aragonite is a calcium carbonate not too different from classroom chalk. If we ever found aragonite in an alien meteorite, we could be very confident that there was life out there. Aragonite is assembled by living organisms or forms in the presence of water. Because it can be eaten by organisms and dissolved in more acidic water (our oceans are increasingly acidic because of CO2 pollution), on a living world, you rarely find it older than 300 million years.

Some of the loveliest nacre in our region is that of orange and yellow jingle shells, an indigeous bivalve mollusk scientifically named Anomia simplex pictured below. HarborLAB volunteers Erik Baard and Caroline Walker gathered these from the Long Island Sound. They were inspired to formulate a HarborLAB outing with children to gather jingle shells and craft gifts for themselves and their families!

Jingle shells. Photo by Erik Baard.

Jingle shells. Photo by Erik Baard.