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Is there life in the sea that hasn’t been discovered? – Haven W., age 12, McKinney, Texas

Imagine going to a place on Earth where no one has ever been. There are many locations like that in the ocean, which covers more than 70% of our planet.

In the ocean, creatures live at many different depths, just as animals and birds live at different heights in a forest. Every ocean life form has to find a way to gather nourishment, reproduce and contribute to an ecological community.

The ocean is thousands of feet deep in many areas and offers millions of opportunities for life to thrive. Biologists don’t know how many species live in the ocean, but they estimate that fewer than 10% have been described.

Fifty years ago, no one imagined that entire biologic communities were thriving in extreme darkness under the crushing pressures of the deep sea. Then they found them, at spots called hydrothermal vents – first with underwater cameras and thermometers, next by sending humans down in Alvin, an underwater vehicle.

The researchers found spots where hot water jetted upward through cracks in the seafloor, like geysers on land. Some of the water was as hot as 750 degrees Fahrenheit (400 degrees Celsius) – more than twice as hot as the oven when you bake a cake. And it was full of dissolved minerals.

As the hot water spilled onto the seafloor, where the water around it was much colder – just 36 F (2 C) – it quickly cooled, and the minerals solidified into stacks that looked like chimneys. Some were tens or hundreds of feet high.

Even in these cold, dark zones, the vents were home to all kinds of living organisms, including giant tube worms, clams, crabs and other species. Sunlight doesn’t reach deep enough in the ocean to serve as an energy source for these communities as it does for ecosystems on land. Instead, these complex ecosystems run on chemosynthesis – energy from chemical reactions between bacteria and the water.

Bacteria that lived in the vents use chemicals such as hydrogen sulfide for energy to make carbohydrates. Then larger organisms feed on the bacteria and the creatures they nourish, and in turn are eaten by still larger creatures, creating a food chain.

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