That all life on the planet can only exist thanks to energy given off by the sun was for a long time taken as a given. After all, plants – thought to the basis of all known food chains until relatively recently – can only grow and make food thanks to the light and heat given off from the sun. But in 1977, undersea geologists working at depths of around 3,000 metres near the Galapagos Islands discovered something that rocked the entire scientific community.
Giant tube worms had been known to science since 1900, when a specimen was dredged up from the bottom of the ocean near Indonesia, but they weren’t seen in their natural habitat until decades later, when submersibles were technologically advanced enough to descend to the sea floor. These giant worms, which can reach up to two and a half metres in length, were found living around ‘black smokers’ – hydrothermal vents where superheated water from the core of the planet comes through the crust. The worms are able to withstand extremely high temperatures and even hydrogen sulphide levels that most other animals would find intolerable.
But the scientists were puzzled. The giant tube worms not only lacked a mouth, but also a gut and an anus. How did they feed? The 1977 dive, and subsequent research, revealed that inside a specialised organ (the trophosome) of the animal lived large quantities of bacteria. There can be so many bacteria within the trophosome, in fact, that they can make up to half of the worm’s entire body weight. The relationship between the tube worm and the bacteria is a symbiotic one; the bacteria turn the hydrogen sulphide and carbon dioxide being spewed out by the hydrothermal vents into organic molecules. Some of these molecules are secreted by the bacteria and used as nourishment by the tube worms.The bacteria, in return, get a safe place within the tube worm to live and reproduce.
This find revolutionised our understanding of some of the basic principles of biology. Here was an animal that obtained its nutrients from chemical energy as opposed to solar energy. Since then, other deep-sea animals, including shrimps, clams and snails, have been found around these hydrothermal vents, all in all comprising unique ecosystems that are completely independent from the life-giving sun above.
The discovery also spurred theories that life could exist on other worlds, even those that are too far away from the sun to receive its warmth and light. The fact that hydrothermal vents are thought to exist on the frozen Jupiter moon of Europa is one of many reasons why scientists believe extraterrestrial life could have evolved in its deep sea. A spacecraft designed to investigate it and similar moons should arrive there by 2030.