Every Earth life relies either directly or indirectly on sunlight and an atmosphere with oxygen. But during the late 1970's, biologists have discovered Riftia pachyptila, chemosynthetic tube worms, that were living around black smoker vents at the bottom of the Pacific Ocean which was not far from the Galapagos Islands, which was also the birthplace of Darwin's theory of evolution by natural selection.

According to an article coming from Scientific American, during the early 1990's Bacillus infernus, a bacterium was discovered just 10,000 feet beneath a farmer's field located in Virginia, where it has been living for over 200 million years. Since then, entire ecosystems have been slowly uncovered that was residing miles beneath the surface and has sustained indefinitely by nothing more than the decaying of radiogenic thorium, uranium, and potassium.

With all of this life flourishing in underneath the Earth's very surface, any science junkie can't help but look at the images of ancient Martian surfaces and wonder if life has also existed beneath its frozen, desiccated surface. According to Portal to the Universe, more than a hundred years ago, American Businessman Percival Lowell believed that he could see evidence of an extraterrestrial civilization that previously lived on the surface of Mars, but that illusion, along with his scientific credibility, was dispelled within fifteen years of his discovery.

In 1901 H. G. Wells, who was a contemporary of Lowell, has also published The First Men in the Moon, in which he constructed an imaginary and fantastically-sophisticated society of insect-like creatures, called Selenites, that were living beneath the lunar surface. Since then, the entire concept of extraterrestrial life has figured frequently in science fiction novels and movies (e.g. Star Trek movies, etc.).

Until now, the search for Extraterrestrial life is still ongoing. Whether it be in novels, or on theories and assumptions that scientists and researchers made, people are constantly looking if a human actually has a companion in this universe.