Yuki Morono and his team at the Japan Agency for Marine-Earth Science and Technology dug up 100 million year old mud from the sea and fed it (Well, not the mud itself, but whatever is hanging out in there).
They grabbed plugs of sediment up to about 70 meters below the seafloor. Very little sediment accumulates here, so that 70-meter-thick pile of clay represents about 100 million years of time.
In case you’re wondering if it can’t just be younger bacteria in the mud, there’s an answer:
The thing is, the researchers don’t think this is just modern bacteria that have made their way deep into the mud. In fact, they shouldn’t be able to move at all in that mud. The average space between particles in the clay should be considerably smaller than the size of a bacterium. The presence of microbes in the oldest sediments represent communities that are about as old as the sediment itself, the researchers conclude.
But back to feeding the mud:
The researchers took these little plugs of sediment and injected substances bacteria can use to grow, like sugar and ammonia. And sure enough, bacteria grew and gobbled them up
So if the researchers are right about what they’ve found, it’s a testament to the fact that life is nothing if not persistent. By slowing down to live within extremely limited means, these bacterial communities may have survived for a simply incredible length of time.