Glowing is a common trick in nature. Bioluminescence, the ability to give off light through a simple chemical reaction, is so useful that it has evolved independently at least 50 different times, and can be found among such diverse lifeforms as mushrooms, fireflies and terrifying deep sea creatures. Whether to ward off predators, attract prey, rid cells of oxygen, or simply cope with living in the perpetual darkness of the deep ocean, bioluminescence is one of life’s most ingenious tools.
These purple, green-rimmed creatures live off the Pacific Coast of North America. Called crystal jellies, they dazzle the deep sea with two distinct kinds of glowing. First, they’re bioluminescent, producing purplish-blue light through a chemical reaction between calcium and the protein aequorian. This light in turn triggers fluorescence around the jelly’s rim: A molecule called green fluorescent protein (GFP) absorbs the purple-blue light and transforms it into green. Since scientists discovered what makes the crystal jelly glow, aequorian and GFP have become important tools in research. For example, they can be injected into other creatures and used to visualize processes inside the body