Mariana Trench

The Mariana Trench was the deepest known point on Earth.

Characteristics
The Mariana Trench was located south of Tokyo and east of Manila. It was believed to be at least eleven kilometres deep. At the bottom, the pressure was a thousand times greater than that at the surface, capable of crushing any normal surface life.

The surface of the trench was covered in volcanic ash and marine snow. This volcanic ash was created by black smokers, which produced superheated water and hydrogen sulphide. (BBCR: Submission)

History
Circa 150 million BC an alien parasite crashed in the Mariana Trench. It lived alone for million years, searching for a host whose memories it could feed on.

In the late 1950s, twin submarines were built to investigate the the Mariana Trench; the Guernica was assembled in Spain and the Trieste in Italy. In 1959 Sam Doyle and Henry Goddard were sent down in the Guernica. The Guernica was scuttled, Sam was infected with the parasite and Henry was killed. The government covered up the incident and claimed the submarine was lost at sea.

In the 1960s, the Trieste was sent down successfully. This would be the last manned attempt in nearly 50 years.

In 2009, Sam had run out of memories and the parasite wanted a new host. The parasite made a call for help that was heard across the world. When the Torchwood Three team came to investigate, it attacked their submarine and planned to infect them next. They were able to escape the parasite using the sunk Guernica, but it was still able to infect Carlie Roberts. The parasite was killed when the Guernica rose too high, depriving it of the hydrogen sulphide in needed. (BBCR: Submission)