James Cameron teams up with NASA scientists to explore the Mid-Ocean Ridge, a submerged chain of mountains that band the Earth and are home to some of the planet's most unique life forms.
IMDB
Aliens of the Deep
The first 18 minutes are a bit slow - equipment failure, get to know the scientists - ho hum. But, after that it really picks up. Excellent photography, interesting critters, etc. Implication for exploration on other planets is covered, and there is a nice twist at the end. Thanks to acousticelectric07 for the link posted in the Family forum. It is duplicated here because it is also a documentary.