(CNN) Barely alive "zombie" bacteria and other life forms are thriving miles below the Earth's surface, scientists have found after a decade of research which changes perceptions of life on our planet.

The discovery of what has been termed a "subterranean Galapagos" was announced by the Deep Carbon Observatory Tuesday, which said many of the lifeforms have lifespans of millions of years.

DCO executive director Robert Hazen said the findings are the "crowning achievement" of the 1,000-strong collective of scientists, who "have opened our eyes to remarkable vistas -- emerging views of life that we never knew existed."

The biomass of the organisms' ecosystem is estimated at 15 to 23 billion metric tonnes (16.6 to 25.4 billion tons), which is hundreds of times greater than that of all human life, and comprises a volume of 2 to 2.3 billion cubic kilometers (480 to 550 million cubic miles) -- almost twice that of all the planet's oceans.

Making use of advances in technology, scientists drilled 2.5 kilometers (1.5 miles) into the seabed and sampled "microbes from continental mines and boreholes more than 5 km deep," a report from the observatory says.

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