The microbes had lain dormant for 100 million years at the bottom of the sea.
Scientists have successfully revived microbes that had lain dormant on the sea floor since the age of the dinosaurs, allowing organisms to eat and even multiply after eons in the deep.
Their research sheds light on the remarkable survival power of some of Earth's most primitive species, which can exist for tens of millions of years with little oxygen or food before coming back to life in the laboratory.
A team led by the Earth and Sea of Japan Science and Technology Agency analyzed samples of ancient sediments deposited more than 100 million years ago on the South Pacific seabed.
The region is known to have far less nutrients in its sediment than normal, making it a far from ideal site to sustain life for millennia.
The team incubated the samples to help lift the microbes out of their once-slumber.
Amazingly, they were able to revive almost all the microorganisms.
"When I found them, I was first skeptical whether the findings are from some error or a failure in the experiment," said lead author Yuki Morono.
"We now know that there is no age limit for organisms in the seafloor biosphere," he told AFP.
URI Graduate School of Oceanography professor and study co-author Steven D’Hondt said the microbes came from the oldest sediment drilled from the seafloor.
"In the oldest sediment that we have drilled, with the least amount of food, there are still living organisms, and they can wake up, grow and multiply," he said.
Morono explained that the traces of oxygen in the sediment allowed the microbes to stay alive for millions of years without spending practically energy.
The energy levels for seafloor microbes "are millions of times lower than those for surface microbes," he said.
Such levels would be too low to sustain surface microbes, and Morono said it was a mystery how the organisms on the seabed had managed to survive.
Previous studies have shown how bacteria can live in some of the least hospitable places on Earth, including underwater vents that lack oxygen.
Morono said the new research, published in the journal Nature Communications, demonstrated the remarkable staying power of some of the simplest living structures on Earth.
"Unlike us, microbes grow their population by divisions, so they don't really have the concept of life expectancy," he added.