Horror and the deep blue sea

Twenty Thousand Leagues Under the Sea published in 1870 by French writer Jules Verne can be considered the first story to introduce the life-forms of the deep blue sea to the public, even if the title is a reference to the distance traveled by the "Nautilus", not the reached depth. The novel was adapted into various movies since 1907. Probably the most well-known adaptation is the version of 1954 with the quite charming special effects and marine scenery.A darker approach to the sea was adopted in the 1989 science fiction movie The Abyss, where the crew of an experimental underwater oil platform encounters strange life forms in a depth of more than 5.500m. The expected success of the movie (the production was so elaborate that the final release was postponed) generated a lot of copycats: Leviathan (1989), DeepStar Six (1989), The Evil Below (1989), Lords of the Deep (1989), and The Rift/Endless Descent (1989) - all these movies follow a very similar plot: the crew of a submarine or underwater station is entrapped with an unknown life form (alien, mutant, sea monster, prehistoric monster) in a confined space. Proteus (1995) and Deep Blue Sea (1999) tried a decade later to revive the genre of underwater horror. DeepStar Six is insofar interesting as the main monster is a surviving prehistoric eurypterid.

Since antiquity, the unknown regions of the oceans were populated by terrible monsters.

Only with the beginning of the age of exploration in the 15th century almost all the monsters vanished slowly from the maps, but still until the 19th century the sea floor remained unknown. It was considered almost impossible that life forms could survive in an environment without light, low temperatures and high pressure. With the first submarine telegraph cables in the mid of the 19th century, it was discovered that life existed also in great depth, as the cables when lifted back to the surface were encrusted by organisms.
The Challenger expedition (1872-1876) was an ambitious research project that recovered samples of the sea floor and described for the first time the life forms of the abyssal zone (4.000-6.000m). However apart from these single glimpses there was no possibility to explore and observe this extreme and vast environment.

January 23, 1960, two men, Jacques Piccard and Donald Walsh, observed for the first time the seafloor at a depth of 10.916m in the Mariana Trench. They were surprised to observe various species of fishes and crustaceans swimming around.

In 1977 the crew of the submarine "Alvin" discovered life forms that dwelled in a self-sufficient ecosystem on a volcanic spot in the eastern Pacific, known as the Galapagos Rift. The hot fluids coming from the hydrothermal vents provided nutrients and minerals used by certain bacteria species to acquire energy from chemical reactions. These bacterial mats provide the base of the ecosystem; some organisms, like giant clams and worms, also host the bacteria in special apposite organs and feed on them. The movie Leviathan (1989) features giant tube worms.
 

Research in the last years has shown that the assemblage of organisms differs between the single spots with hydrothermal vents. For example the classic tube worms Riftia pachyptila and giant clams Calyptogena magnifica are found only in the eastern parts of the Pacific Ocean. In the Scotia Sea we find the "Yeti-Crab" Kiwa hirsute. Based on the species-association at least eleven types of hydrothermal vent biota were proposed.

Alien (1979) - A Creature Feature Review

In the movie "Alien" (1979) the spaceship "Nostromo" is attacked by a life-form encountered on LV-426, a barren Moon orbiting a gas giant in the Zeta Reticuli system, 39 light years away from Earth. According to the lore in the Alien universe, it is a world of volcanic origin, covered in rocks like granite and basalt. The moon's indigenous atmosphere was described as "primordial", consisting mainly of nitrogen, water vapor, carbon dioxide, trace particles of oxygen and small concentrations of methane and ammonia.  

When Alien was released it quickly terrified audiences worldwide. Its unexpected mix of classic horror motives, a relentless predator is killing one by one the crew of a ship, and science-fiction, its a spaceship and the killer is a completely alien life-form, got at first mixed reviews, however, over the years Alien had come to be regarded as one of the best horror and science-fiction films ever made. In the early 70s Dan O'Bannon had written a dark science-fiction comedy film - Dark Star - featuring a cheap looking alien invading a space ship lost in space. O'Bannon recognized the potential of the story and wanted to do a more serious alien film. He began to work on a story involving the discovery of an alien life-form on a remote planet. During a work-related visit to Paris he discovered the artwork of Chris Foss, Moebius and especially H.R. Giger, giving him more ideas for his story. In collaboration with Ronald Shusett and using an early story involving Gremlins infiltrating a B-17 bomber during World War II. he finished the script. After noting the number of times the word alien appeared in the script the project was called Alien. In Alien the crew of a mining vessel has to deal with a fast growing alien life-form hiding inside the air conducts of the spaceship. Shusett suggested that one of the crew members be implanted with an alien parasite to explain how the life-form, discovered at first as egg in a derelict alien spaceship, came on board of the ship. 

The Alien is supposedly a perfect silicon-based life form. According to canon the incarnation of the extraterrestrial xenomorph - as imagined by Swiss artist H.R. Giger - is protected by an outer silicious skeleton from environmental factors, surviving even for a short period in outer space. This resistant shell is also very useful to contain the acid blood of the creature or to merge with its mechanical environment.