Russian scientists have breached an ice sheet that has sealed subglacial Lake Vostok in Antarctica for more than 20 million years at a depth of nearly 4,000 meters, reaching a critical stage in a decades-long drilling project, RIA-Novosti reported.

Lake Vostok is the largest of a network of hidden subglacial Antarctic lakes that was discovered in the 1990s, capturing the attention of scientists around the world. It is also one of the largest lakes in the world.

Scientists believe that a hydrostatic seal created by the surrounding ice cap has kept the lakes completely separated from external contaminants. Potential applications of the recent breakthrough could include the discovery of new life, hints about pre-ice age evolution and give a glimpse of how life exists in extreme conditions.

Rumors that these lakes were also home to secret German submarine bases during World War II are also being revisited in the wake of renewed excitement, driven by Nazi claims that they had created an "unassailable" Antarctic fortress and by archival evidence describing the construction of ice caves.