The Laurentian Abyss is the deepest part of the Earth's oceans at a depth of 6,000 meters (20,000 ft). It is third only to Challenger Deep which has a depth of about 11,000 meters (about 36,000 feet) and the Puerto Rican Trench.
The United States government dropped all of the defeated decepticons into the Laurentian Abyss. It was hoped that the extreme pressure and temperature of the Abyss would destroy bodies of the Decepticons, hiding the evidence from the unknowing populace of Earth. The area was then surrounded by roving warships to prevent Megatron from getting revived. See how well that worked out (look under this trivia bit).
Revenge of The Fallen film
Mixmaster, Long Haul, Skipjack, Ravage, Scalpel, and Scrapmetal go down to the Laurentian Abyss to revive Megatron. The little one dies in the process, and Megatron smashes a nuclear fast attack Los Angeles class submarine as he comes to the surface.
- John Keller calls the abyss the deepest point on Earth... but in reality, this is untrue. The Marianas Trench is 5,000 meters deeper than the Laurentian Abyss. Granted, "Laurentian Abyss" sounds more sci-fi menacing than "Marianas Trench"... which sounds like a Pizza Hut gimmick.