As a human, it’s easy to forget about bioluminescence. Fireflies come first to mind for many of us. But fireflies are rapidly disappearing as people destroy their habitats, increase light pollution, and inundate them with pesticides. In many historically-prolific firefly habitats, you’re now lucky to see even one.
Deep sea life, for the time being, is safer from human activities. And down there, bioluminescence is common. That’s where it comes from, after all: the ability to glow first evolved in a prehistoric ocean, though it has since evolved at least 94 separate times on Earth.
That’s probably because it’s so useful. Especially in deep dark seas, light is a compelling way to communicate with potential mates, lure prey, or scare off would-be predators. The vast majority of bioluminescent life remains in the oceans today.
The early evolution of life is largely a mystery, and we’re still figuring out how bioluminescence first appeared on Earth. Recently, an international research team traced bioluminescence back to 540 million years ago, in ancient coral. That’s about twice as old as it was previously thought to be. (It’s certainly possible that bioluminescence evolved even earlier, but this is an important step in tracing the origins.) For context, researchers think multicellular life evolved some 600 million years ago.
As the prehistoric oceans began to glow, light-sensitive eyes were evolving, too. The living world was finding new ways to connect.
Most coastal corals don’t glow, but many deepwater corals still do. Bioluminescence remains especially useful in places with little or no sunlight. Scientists still aren’t quite sure why deep sea corals glow, but it may have something to do with attracting bigger marine predators to eat the coral-eating species. There are likely many bioluminescent corals in the deep sea that we haven’t found yet, as well as countless other glowing species still undiscovered.
Bioluminescence in the deep can be hard for humans to study and understand. Images of deep sea life are often taken with bright light. While this lets us see clearly, it also erases the sense of what life down there is really like: a shifting, sparkling, glowing world.
Disruptions from deep sea mining, like sediment plumes, could block the luminous displays deep sea animals depend on. (That’s in addition to the other possible damage from sediment plumes, like oxygen depletion.) For all the remarkable adaptations of life on Earth, few of them stand up well to modern industrialization.