Deep-Sea Life Without Sunlight
Contrast photosynthesis (energy from sunlight) with chemosynthesis (energy from oxidising chemicals like hydrogen sulphide); describe hydrothermal vent communities: chemoautotrophic bacteria form the base of a food web supporting tube worms, giant clams, and vent crabs with no sunlight; explore what deep-sea life tells us about the origin of life on Earth; explain why NASA studies ocean vents as analogues for potential life around hydrothermal activity on Europa and Enceladus
The lesson
Nearly everything alive on Earth depends on the sun, directly or indirectly. Plants use sunlight to make food, and most animals eat plants or animals that ate plants. But thousands of metres down on the ocean floor, sunlight never reaches at all. There, whole communities of animals thrive around cracks called hydrothermal vents, and none of them rely on the sun.
Hydrothermal vents spray out hot water loaded with a chemical called hydrogen sulphide. Certain bacteria living around the vents take in that hydrogen sulphide and combine it with oxygen, releasing energy they use to build food. This process is called chemosynthesis. It does the same job as photosynthesis, turning simple ingredients into food, but it runs on chemical energy instead of light.
Giant tube worms living at the vents have no mouth and no stomach. Instead, they carry chemosynthetic bacteria inside their bodies and live off the food the bacteria make. Giant clams do something similar, housing bacteria in their gills. Vent crabs scurry over the rocks, grazing on thick mats of bacteria and hunting smaller animals. Every one of these animals traces its food back to bacteria eating chemicals, not to sunlight.
Because chemosynthesis needs no sunlight, scientists think life on Earth may have first appeared near vents like these, long before there was enough oxygen for today's food chains. That idea is why NASA studies vent communities closely: if life can start and survive on chemical energy alone, it might also exist in the hidden oceans below the icy surfaces of Jupiter's moon Europa or Saturn's moon Enceladus, both of which show signs of their own hydrothermal activity.
Deep-sea vent life runs on chemosynthesis, energy from chemicals like hydrogen sulphide, not sunlight, and studying it shapes the search for life on icy moons like Europa and Enceladus.
Watch it
Where it sits
Learn first
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.