Scientists routinely gather sediment samples from beneath the seafloor to get a better understanding of ancient climates, plate tectonics, and the deep marine ecosystem. A recently published study reveals that the researchers have found that microbes collected from sediments beneath the seafloor that are as old as 100 million years can revive and multiply. These microbes have been lying dormant since dinosaurs roamed the earth.
The ancient sediment samples covered in the new study were gathered ten years ago during an expedition to the South Pacific Gyre, which is part of the ocean with the lowest productivity and fewest nutrients available for marine life. The researchers say their main question was whether life could exist in such a nutrient-limited environment or if the region was a lifeless zone.
Scientists also wanted to determine how long the microbes were able to sustain their life in the near-absence of food. Microbes become trapped in the seafloor sediment, where there may be no food to support them. The sediment cores used in the study were sourced 100 m below the seafloor and nearly 6000 m below the ocean surface.
One surprise was that the researchers found that oxygen was present in all of the cores, which suggested that the sediment accumulated slowly at a rate of no more than a meter or two every million years. Oxygen will penetrate from the seafloor to the rocky basement under the sediment with conditions supporting aerobic microorganisms requiring little oxygen to live.
The researchers incubated samples of the microbes to get them to grow. The results showed that rather than being fossilized remains of life, the microbes in the sediment were alive incapable of growing and dividing. The team says that up to 99.1% of the microbes in the sediment deposited 101.5 million years ago were active and ready to eat.