The microorganisms were collected by Japanese scientists a decade ago in sedimentary layers located in a region of the Pacific where life is rare.
In a new study published this week in the journal Nature Communications, researchers from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) managed to revive microorganisms over 100 million years old.
“Our main question was whether life could exist in such a nutrient-limited environment or if this was a lifeless zone,” said Yuki Morono, the study’s leader. “And we wanted to know how long the microbes could sustain their life in a near-absence of food.”
At the bottom of the sea, there are layers of organic sediments from dust and particles that are carried by the wind and ocean currents. Several types of microorganisms are trapped in this debris – and it was exactly these microbes that the researchers decided to investigate.
Using a drillship, scientists drilled sediment cores 100 meters below the seabed, almost 6000 meters below the sea surface. The scientists found that oxygen was present in all explored regions, suggesting that if sediment slowly accumulates on the seabed at a rate of no more than one or two meters every 1 million years, oxygen will be present in these layers.
The samples of microorganisms collected were incubated and fed for a long time – and then came the surprise: the vast majority of the microbes were still alive. “At first I was skeptical, but we found that up to 99.1% of the microbes in sediment deposited 101.5 million years ago were still alive and were ready to eat,” Morono said.
The research team plans to use the same approach in other geological studies. According to Morono, the life of these microorganisms is much slower than ours and, therefore, their evolutionary speed is also slower. “We want to understand how or if these ancient microbes evolved,” the researcher said. “This study shows that the subseafloor is an excellent location to explore the limits of life on Earth.”