In a world without sun, the animals of the deep sea have no choice other than to illuminate their own lives and glow in the dark.
Light in the abyss:
Sunlight only penetrates the top 100 metres (330 feet) of the ocean, and animals that live below the reach of the Sun’s rays experience constant darkness. There are several zones to the ocean from the sunlight or photic zone at the surface all the way down through the twilight and midnight zones to the abyssal zone at 4,000 to 6,000 metres (13,100 to 19,700 feet) deep. This water is completely devoid of light, but is home to hundreds of weird and wonderful marine species that humans have had to develop highly specialised equipment to even glimpse. Animals have even been found living below the abyssal zone, at such dark depths that it’s almost unsurprising that some have evolved to generate their own light.
“At such dark depths it’s almost unsurprising that animals have evolved to generate their own light”
Bioluminescence, a natural glow produced by an organism, is a chemical process involving a substance called luciferin. When this molecule comes into contact with oxygen it produces a chemical called oxyluciferin and the by-product is light. While only a handful of terrestrial animals have this capability, it’s relatively common in the sea. where it has evolved numerous times. This demonstrates how crucial it is to be able to produce light, and for some species it’s the difference between survival and death.