Scientists have brought back to life microbes found in 100-million-year-old sediment from deep beneath the ocean floor. The experiment sheds new light on where on Earth life can be found — and just how resilient it can be.
According to a new study published in the journal Nature Communications, microbes found buried below the seafloor have persisted for up to 101.5 million years. The sediments do not have the energy required to allow cells to sustain themselves, but scientists were still able to revive the communities.
It's a mystery how the microbes were able to survive the harsh conditions of their surroundings — and it's unclear just how long they can live. Researchers said they could possibly be the planet's oldest-known organisms.
Scientists at the Japan Agency for Marine-Earth Science and Technology analyzed sediment samples found approximately 12,140 to 18,700 feet beneath the ocean surface in the South Pacific Gyre, a system of rotating currents located in the Pacific Ocean. The center of the South Pacific Gyre contains the "oceanic pole of inaccessibility," the site on Earth farthest from all land — the lowest-productivity part of the entire ocean.
The area has little food, but it does harbor a lot of oxygen deep beneath the subseafloor. The sediment layers, collected during a 2010 expedition, were deposited over a period from 13 million to 101.5 million years ago.
Within the sediment, scientists found marine microbes: tiny, single-celled microorganisms that make up the overwhelming majority of the total mass of living creatures in the ocean. Trapped in the sediment layers, they could barely move or eat.
The researchers wanted to know if life can exist in such a nutrient-poor environment.
Back in the lab, researchers were able to rouse the microbes from their lengthy slumber. They gave the ancient samples carbon and nitrogen substrates, to test whether they were cable of feeding and dividing into more cells.
Over a period of 68 days, the vast majority of the nearly 7,000 cells rapidly responded to the new conditions, multiplying by four orders of magnitude — even in the oldest samples. Researchers said aerobic bacteria dominated the experiment.
"What we found is that life expends all the way from the seafloor to the underlying rocky basement," University of Rhode Island oceanographer and study co-author Steven D'Hondt said in a video news release. "Those organisms are not only alive in the deepest, oldest sediment, but they're capable of growing and dividing."
"It is surprising and biologically challenging that a large fraction of microbes could be revived from a very long time of burial or entrapment in extremely low nutrient/energy conditions," lead author Yuki Morono told Reuters.
The research indicates that microbes could survive for previously unfathomable lengths of time if sediment accumulates at a very slow pace, trapping oxygen over time.
Through further experiments, researchers now hope to determine how the microbes were able to persist for millions of years.
"The most exciting part of this study is that it basically shows that there is no limit to life in the old sediment of Earth's ocean," D'Hondt told Reuters. "Maintaining full physiological capability for 100 million years in starving isolation is an impressive feat."