Scientists believed that only small animals lived at the ocean bottom in seafloor sediments. These animals received their food from above. The food chain depended on sunlight and photosynthesis, just as the food chain on land does. Here’s how it works:

In the sunlit ocean surface, microscopic marine plants called phytoplankton flourish-like great fields of grasses on land. Marine animals eat the phytoplankton much the way insects or zebras eat plants on land. And predators eat other animals.

When all these marine plants and animals die, they sink to the bottom. This organic material rains down to feed bottom-dwelling (or “benthic”) animals. Occasionally, the carcass of a dead whale might sink down to provide a feast! Scientists had thought this was the only way life could survive on the deep seafloor.

The discovery of hydrothermal vents changed all that. Vast communities of animals grew big and fast in the depths! Instead of using light to create organic material to live and grow (photosynthesis), microorganisms at the bottom of the food chain at vents used chemicals such as hydrogen sulfide (chemosynthesis).

At the seafloor, thriving ecosystems receive energy from a source that had never been thought of before-heat and chemicals from the planet itself. The energy to sustain life was not coming down from the sun. It was coming up from the interior of the earth.

Intro

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