Yet scientists have discovered microscopic creatures that somehow manage to thrive in the eternal darkness. By searching the cracks and crevices of the cave, they hope to answer a question that has been plaguing mankind for centuries: Is there life on Mars?
The subterranean research has piqued NASA's interest.
"The work is very relevant to Mars because we know the surface of Mars is as dead as a doornail and any life there, if it exists, would live underground," said Chris McKay, a planetary scientist at NASA's Ames Research Center in Moffett Field, Calif.
Spider Cave, in Carlsbad Caverns National Park, feels very much like another planet. Stalactites protrude from the cave's ceiling, reaching out like great tentacles. And gaping pits, like giant moon craters, are scattered haphazardly across the cave floor. The silence is deafening.
Caves are isolated ecosystems low in organic nutrients. But the microbes in the Spider Cave can survive without sunlight and survive on basic elements such as iron, manganese and sulfur found in the cave walls. Researchers have found similar microbes living in other remote places like polar caps, ocean bottoms and mountain peaks.
Scientists think life might be able support itself on a planet like Mars by feeding on underground chemicals, similar to the way bacteria in Spider Cave survive.
Wearing protective gear and hard hats with spotlights, scientists trek to Spider Cave's research site by hiking down a mile-long, winding trail and over rugged terrain into a canyon. That's when the going gets tough.
They then descend 10 feet to the first narrow opening and squeeze through a tight, 50-foot passage.
"It's like being born again," quips geology student Justin Pearce.
After the first belly crawl, the cave opens into an intricate web of passages that run up to four miles in every direction. A marked trail keeps researchers from getting lost.
The quest for microscopic organisms may not be as flashy as the search for intelligent life in outer space, but NASA's McKay says it's just as important.
"If you look at our own planet, for half of its history, life was microscopic. It's the first step to more complicated life."