Scientists drilling into sediment beneath the South Pacific Gyre pulled up microbes from seabed layers as old as 101.5 million years. Starved in one of the poorest habitats on Earth, many of the cells were still viable: when given nutrients under oxygen-bearing laboratory conditions, they repaired their metabolism, took up carbon and nitrogen, and began to multiply. They are among the oldest microbial communities ever revived from dormancy.

In 2020, scientists reported that they had drilled into sediment beneath the South Pacific Gyre and recovered microbes from layers as old as 101.5 million years. The sediment had been laid down in the Cretaceous, when dinosaurs still dominated the land. The cells were buried in one of the poorest habitats on Earth, with almost no food arriving from the ocean above. Yet many of them were still viable.

Given nutrients under oxygen-bearing laboratory conditions, the cells reactivated. They took up carbon and nitrogen and began to divide. They are among the oldest microbial communities anyone has revived from a near-dormant, ultra-slow state.

Where the sediment came from

The samples were collected in 2010, during Integrated Ocean Drilling Program Expedition 329, aboard the research drillship JOIDES Resolution. The target was the abyssal plain of the South Pacific Gyre, a stretch of open ocean far from any land, under about 5,700 metres of water. The team drilled around 75 metres into the seafloor and recovered sediment spanning from 4.3 to 101.5 million years old.

The South Pacific Gyre was chosen because it is, biologically, close to empty. It is the least productive part of the ocean, the region with the fewest nutrients feeding the marine food web. So little organic matter rains down onto the seabed there that the sediment never runs out of oxygen. Most deep sediment is oxygen-free within centimetres of the seafloor, because microbes consume the oxygen as they break down organic material. Here there is so little to break down that oxygen reaches all the way down to the underlying rock.

That oxic condition turned out to matter, because it is aerobic, oxygen-using microbes that the study found had survived.

What they did, and what they measured

The test was direct. The researchers, led by Yuki Morono of the Japan Agency for Marine-Earth Science and Technology, incubated the old sediment with carbon and nitrogen compounds that had been tagged with heavy isotopes, so that any cell taking them up would carry a detectable label. The incubations were run under low-oxygen, microaerobic conditions, with about 3.3 per cent oxygen, in keeping with the naturally oxygenated sediment. Then they looked, cell by cell, to see which cells were eating.

They examined 6,986 individual cells using a technique called NanoSIMS, which measures the isotopic make-up of single cells. Most of the cells had taken up the labelled carbon and nitrogen. In the paper, published in Nature Communications, the team reported that the populations grew by four orders of magnitude within 68 days of incubation, and that uptake of nitrogen was on average about three times faster than uptake of carbon. In the oldest sediment, the estimated revivable heterotrophic fraction ranged as high as 99.1 per cent.

The revival was specific. Aerobic microbes came back readily. Anaerobic ones, which do not use oxygen, were barely revived at all, consistent with an environment that had held oxygen the whole time.

Dormant, or just very slow

The headline version of this is that the microbes lay dormant for a hundred million years and then woke up.

The careful version is a little different.

What the dating establishes is the age of the sediment, not a stopwatch on any single cell. The reasonable inference is that the microbial community was buried with the sediment and persisted in place ever since, but the study does not prove that each cell is literally 101.5 million years old. Whether the cells were truly suspended, with metabolism switched off, or ticking over at a rate too slow to measure, is not something the study fully resolves. Research on energy-starved life beneath the seafloor suggests these organisms live at metabolic rates far below anything seen in a normal laboratory culture, slow enough that the line between sleeping and barely living starts to blur. What the experiment shows cleanly is that the cells retained the machinery to recover once conditions allowed.

Why the contamination controls matter

Claims about extremely ancient revived microbes have a difficult history, because the obvious failure mode is contamination. A modern cell that slips into a sample during drilling or handling can masquerade as an ancient survivor. An earlier and much-cited claim, of bacteria revived from a 250-million-year-old salt crystal, reported by Russell Vreeland and colleagues in Nature in 2000, has been disputed for exactly this reason. Critics noted that the revived strain’s genetic sequence was almost identical to a modern salt-loving bacterium, which is hard to reconcile with a 250-million-year separation and points instead to contamination.

This is where the South Pacific Gyre work is stronger than most. The team tracked chemical tracers from the drilling fluid and found contamination minimal, below detection in some key samples. Morono’s group is also known for stringent clean handling, and the single-cell isotope method adds another layer: it does not merely show that something grew after incubation, it shows that the specific cells present in the old sediment took up the labelled food. That makes the case that these were genuinely the buried organisms, rather than later arrivals, harder to dismiss. It is why the result sits among the better-evidenced of the very old revivals, even though older claims exist.

What it changes

The reach of the finding is in what it implies about the limits of life. If aerobic microbes can persist for a hundred million years on almost no energy, sealed in cold sediment with oxygen and little else, then the conditions under which life can hold on are broader than a tally of thriving ecosystems would suggest. Steven D’Hondt of the University of Rhode Island, a senior author, put the point plainly in the university’s announcement: in the oldest, least nourished sediment they had drilled, there were still living organisms able to wake up, grow and multiply.

That has a bearing beyond Earth. Places that look inhospitable because they are starved of energy, such as the cold subsurface of Mars or the interiors of icy moons, are exactly the kind of setting where this study suggests life, if it ever started, might simply wait. The open questions now are mechanical: how a cell holds itself together for such spans, what minimal trickle of energy it needs, and how slow a living thing can go without crossing over into being a dead one. The microbes from beneath the gyre do not answer those questions. They make them harder to wave away.