The preserved remains of prehistoric humans and animals and indications of early human culture have been discovered in some caves. Caves have served as burial grounds and shelter since prehistoric times. One such cave is Alabama's Russell Cave, where human evidence dates back 9,000 years. Speleology, the scientific study of caves and their plant and animal life, contributes to knowledge of biological adaptation and evolution. Some cave animals lack sight, and both plants and animals living where light is excluded show loss of pigment. Deep cave ecosystems, lacking the sunlight necessary for photosynthesis, depend on bacteria that use chemosynthesis to create energy.
Among famous caves in the United States are Carlsbad Caverns National Park (N.Mex.), Mammoth Cave National Park (Ky.), Wind Cave National Park (Black Hills, S.Dak.), Luray Caverns (Va.), and Wyandotte Cave (Ind.). In Europe there are celebrated caves in Belgium, Dalmatia, Gibraltar, Capri, Sicily, Postojna, and England (Kent's Cavern and Kirkdale). The caves of the Pyrenees and the Dordogne are famed for their prehistoric paintings (see Paleolithic art), and those of Ajanta, India, and Dunhuang, China, for their Buddhist frescoes. Among the deepest known caves are Krubera in the nation of Georgia, which extends more than 6,500 ft (2,000 m) below the surface, and Lamprechtsofen in Austria.
See C. E. Mohr and T. L. Poulson, The Life of the Cave (1966); D. R. McClurg, The Amateur's Guide to Caves and Caving (1973).
A cave is a natural underground void large enough for a human to enter. Some people suggest that the term cave should only apply to cavities that have some part that does not receive daylight; however, in popular usage, the term includes smaller spaces like sea caves, rock shelters, and grottos.
Speleology is the science of exploration and study of all aspects of caves. Exploring a cave for recreation or science may be called caving, potholing, or, in Canada and the United States, spelunking (see Caving).
The cave system with the greatest total length of surveyed passage is Mammoth Cave (Kentucky, USA) at in length. This record is unlikely to be surpassed in the near future, as the next most extensive known cave is Jewel Cave near Custer, South Dakota, at .
The deepest known cave (measured from its highest entrance to its lowest point) is Voronya Cave (Abkhazia, Georgia), with a depth of . This was the first cave to be explored to a depth of more than . (The first cave to be descended below was the famous Gouffre Berger in France). The Illyuzia-Mezhonnogo-Snezhnaya cave in Abkhazia, Georgia, and the Lamprechtsofen Vogelschacht Weg Schacht in Austria are the current second- and third-deepest caves. The deepest cave record has changed several times in recent years.
The largest individual cavern ever discovered is the Sarawak chamber, in the Gunung Mulu National Park (Miri, Sarawak, Borneo, Malaysia), a sloping, boulder strewn chamber with an area of approximately by and a height of .
Cave-inhabiting animals are often categorized as troglobites (cave-limited species), troglophiles (species that can live their entire lives in caves, but also occur in other environments), trogloxenes (species that use caves, but cannot complete their life cycle wholly in caves) and accidentals (animals not in one of the previous categories). Some authors use separate terminology for aquatic forms (e.g., stygobites, stygophiles, and stygoxenes).
Of these animals, the troglobites are perhaps the most unusual organisms. Troglobitic species often show a number of characteristics, termed troglomorphies, associated with their adaptation to subterranean life. These characteristics may include a loss of pigment (often resulting in a pale or white coloration), a loss of eyes (or at least of optical functionality), an elongation of appendages, and an enhancement of other senses (such as the ability to sense vibrations in water). Aquatic troglobites (or stygobites), such as the endangered Alabama cave shrimp, live in bodies of water found in caves and get nutrients from detritus washed into their caves and from the feces of bats and other cave inhabitants. Other aquatic troglobites include cave fish, the Olm, and cave salamanders such as the Texas Blind Salamander.
Cave insects such as Oligaphorura (formerly Archaphorura) schoetti are troglophiles, reaching in length. They have extensive distribution and have been studied fairly widely. Most specimens are female but a male specimen was collected from St Cuthberts Swallet in 1969.
Bats, such as the Gray bat and Mexican Free-tailed Bat, are trogloxenes and are often found in caves; they forage outside of the caves. Some species of cave crickets are classified as trogloxenes, because they roost in caves by day and forage above ground at night.
Because of the fragile nature of the cave ecosystem, and the fact that cave regions tend to be isolated from one another, caves harbor a number of endangered species, such as the Tooth cave spider, Liphistiidae Liphistius trapdoor spider, and the Gray bat.
Caves are visited by many surface-living animals, including humans. These are usually relatively short-lived incursions, due to the lack of light and sustenance.
Throughout history, primitive peoples have made use of caves for shelter, burial, or as religious sites. Since items placed in caves are protected from the climate and scavenging animals, this means caves are an archaeological treasure house for learning about these people. Cave paintings are of particular interest. One example is the Great Cave of Niah, in Malaysia, which contains evidence of human habitation dating back 40,000 years.
Caves are also important for geological research because they can reveal details of past climatic conditions in speleothems and sedimentary rock layers.
Caves are frequently used today as sites for recreation. Caving, for example, is the popular sport of cave exploration. For the less adventurous, a number of the world's prettier and more accessible caves have been converted into show caves, where artificial lighting, floors, and other aids allow the casual visitor to experience the cave with minimal inconvenience. Caves have also been used for BASE jumping and cave diving.
Caves are also used for the preservation or aging of wine and cheese. The constant, slightly chilly temperature and high humidity that most caves possess makes them ideal for such uses.