The Integrated Ocean Drilling Program was chosen to bore into the gabbroic layer by starting at the ocean floor in the mid-Atlantic.
Seismic forces there have pushed the target layer to within hundreds of feet of the seabed, making it easier to reach.
A team from Oregon State University found unique types of bacteria there, which feed off hydrocarbons like methane and benzene, similar to microorganisms present in underground oil deposits.
The researchers believe that since oil and gas could also be present in the mantle below, the tenacity of life could allow organisms to be present at even much greater depths.
The findings are published in the journal PLoS ONE.