Life without the sun
Deep within the Kugitangtau mountains, a limestone range in southeastern Uzbekistan, the Chakchar Cave system holds a biological anomaly. It is a place that runs without sunlight. The ecosystem here is not based on photosynthesis, the process that powers nearly all life on the surface. Instead, its foundation is chemosynthesis: the creation of energy from chemical reactions.
The cave's water is high in hydrogen sulfide (H2S), a gas that smells of rotten eggs and is toxic to most familiar forms of life. This gas seeps from deep geological sources into the cave's streams. Here, specialized bacteria oxidize the hydrogen sulfide. They oxidize the hydrogen sulfide, harnessing the chemical energy released in the reaction to produce organic matter. These chemoautotrophic bacteria form the base of the entire food web, creating thick white and orange mats on the rocks and in the water. Similar ecosystems, completely isolated from the sun, exist around deep-sea hydrothermal vents and in a few other specialized caves around the world, like Movile Cave in Romania and Cueva de Villa Luz in Mexico.