80-square mile kill zone Gulf of Mexico - "It looks like everything's dead"

A mile below the surface in the Gulf of Mexico, there is little sign of life. "It looks like everything's dead," University of Georgia professor Samantha Joye said.

In an exclusive trip aboard the U.S. Navy's deep-ocean research submersible Alvin, ABC News was given the chance to observe the impact of this summer's massive oil spill that most will never see.

The ocean floor appears to be littered with twigs, but Joye points out that they are actually dead worms and that Alvin is sitting on top of what is considered an 80-square mile kill zone.

Having taken nearly two dozen dives in the Gulf inside the tiny sub that helped discover the Titanic, Joye is leading a team of scientists who are investigating how much oily material is left on the sea floor.

Aboard the Alvin Thursday, Joye said she saw "about three to four inches of material."

The devastation, she said, could last "years or decades."