The deep ocean floor is an environment where photosynthesis is impossible because sunlight never reaches it, but with the help of hydrothermal vents and chemosynthetic bacteria, organisms like Leptia survive and thrive in this extreme environment.
The average depth of the world’s oceans is nearly 4,000 meters, representing the vast depths of the ocean, which covers about 71% of the Earth’s surface. In these deep waters, there are large areas where sunlight never reaches. Because solar energy can’t reach them, and primary producers of photosynthesis can’t survive, the ecosystems here are sustained in a completely different way than surface ocean ecosystems. These are extreme conditions unlike any other environment on Earth, and the animals that live on the deep ocean floor are forced to rely on organic matter that eventually falls from the surface of the ocean to the seafloor. This organic matter, called “marine snow” because it’s the residue left over from the decomposition of marine organisms, provides the basis for life in even the deepest parts of the ocean. However, the amount of this organic matter is very limited, and by the time it reaches the bottom of the ocean, there is very little left. This makes it very difficult for large numbers of organisms to survive on the deep ocean floor, which is why the deep ocean is often referred to as the “desert of the earth” and raises questions about how organisms survive in such a harsh environment with extremely few resources.
But life has always found new ways to survive. In 1977, one of the most exciting discoveries in the history of biology took place. At the time, oceanographers were very interested in exploring the deep sea, and one team was using the submersible Alvin to explore the undersea mountains near the Galapagos Islands in the eastern Pacific. As they explored the deep ocean floor, they saw something they never expected to see. There, where the sun’s energy never reaches, they found an unexpectedly large community of organisms, all of which were completely new species that scientists had never seen before.
Hydrothermal vents, located on the ocean floor at depths of thousands of meters, have temperatures significantly higher than the surrounding seawater due to the hot effusions from tectonic activity. This hot seawater contains a variety of minerals and large amounts of hydrogen sulfide, and these extreme conditions create a unique ecosystem found nowhere else on Earth. In some places, hydrothermal vents spew seawater over 350 degrees Celsius, and the black, sooty, chimney-like structures they form are created by the precipitation of minerals. These hydrothermal vents reveal the birth of entirely new ecosystems fueled by the energy of the Earth’s interior, providing a new perspective on the evolution of life on Earth.
The dominant species in deep-sea hydrothermal vents are large tubular worms called “leafhoppers,” which have a uniquely evolved way of feeding. They have no mouth or digestive system, and instead have specialized organs called ‘trophosomes’. These organs are filled with bacteria and play a key role in the worm’s survival. The body of the leafhoppers sits inside the long tube, and the bright red feathery structures that project outward from the tube act like gills, exchanging carbon dioxide, oxygen, and hydrogen sulfide. This specialized physiological structure allows the tube worm to survive in the extreme conditions of the deep ocean, and this evolutionary adaptation is a remarkable testament to the diversity and vitality of deep-sea life. To sustain their lives, tubeworms form symbiotic relationships with bacteria, a unique ecological interaction that is not found in any other ecosystem on Earth.
The discovery of deep-sea hydrothermal vents ecosystems has completely changed the way we view Earth’s ecosystems, where chemosynthetic bacteria serve as primary producers like phytoplankton that photosynthesize in the surface layers of the ocean. These ecosystems don’t rely on solar energy at all, and entirely new forms of life are evolving based on the energy and chemistry of Earth’s interior. This has allowed scientists to explore new possibilities for the origin and evolution of life on Earth, and is also providing important clues to the search for possible extraterrestrial life. The discovery of life in deep-sea hydrothermal vents is an important example of how life on Earth can survive in a wide variety of environments, and it continues to spark our imagination.
