Back when the dinosaurs ruled the Earth, some hardy bacteria took up residence at the bottom of the Pacific Ocean. Eighty six million years later, they're still there. And a new study says they're living out the most Spartan lifestyle known on this planet.
They live in a place called the Pacific Gyre, where almost nothing reaches the seafloor. Nutrients from the world's rivers don't get out that far. Most plankton that die in the water dissolve long before any pieces of them can reach the seafloor far below. It's a rare day indeed when even a single particle lands in any given spot on the bottom.
"If you imagine that a grain of sediment falls on the surface, it will take a thousand years before the next grain will sit on top of it," says Hans Roy at Aarhus University in Denmark.
As a result, it has taken millions of years for a thin layer of sediment to form.
Roy was part of an expedition in 2009 to sample that ancient sediment. And amazingly enough, he found living bacteria buried in that clay. That's amazing because there are almost no nutrients down there for them to feed on.
"They left the surface 86 million years ago with one lunch box, and they're still eating out of it," Roy says. "It's like they're splitting a pie, and they keep splitting in half and in half and in half, but nobody ever eats the last crumble. It's quite remarkable."
Roy and colleagues report their find in the latest Science magazine. They say these bacteria may have the world's slowest metabolism, with barely enough oxygen and nutrients to keep them alive.
"I weigh 140 pounds, and I eat a few pounds of food every day, so it will take me a month or two to eat my own weight," Roy says. "These organisms will take a thousand years to eat their own weight."
'In Our Eyes It Looks Like Suspended Animation'
Roy can't say exactly how old the individual bacteria he studies are. They may have been reproducing extremely slowly since the time of the dinosaurs. Or the individuals could be millions of years old, rebuilding themselves just fast enough to repair the inevitable damage of aging.
In any case, these microscopic life-forms have life cycles that defy human intuition.
"That's so much slower than our own, that in our eyes it looks like suspended animation," Roy says. "This is pretty much like if you would stand up and look at a tree to see if it grows at all, you won't see anything because you're looking at the wrong time scale."
Happily, nature has run that experiment on the seafloor.
One reason scientists are interested in this extreme lifestyle is because it provides clues about the absolute minimum conditions required to sustain life. Andreas Teske, a marine microbiologist at the University of North Carolina, Chapel Hill, says that's useful for people looking beyond our planet for signs of life.
"We would like to know how far down can we go with respect to energy supply for life," says Teske. "So we have to look at the most difficult places for life on Earth. And the deep subsurface is certainly one of these most difficult, and at the same time — just by volume, by space, by extent — one of the most dominant places on Earth."
So these bacteria are likely quite abundant, and they're very likely to be here long after we're gone.
"These organisms have no clue that we're even around," Roy says. "They could be sitting down there for 100 million years, and the whole surface could be one scorched desert, and they still wouldn't know it."
On the other hand, we, presumably, have more fun.