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What is the oldest living thing on Earth? We've found two hundred and 50 year old tortoises, 5,000 year old trees, and even 11,000 year old sponges living at the bottom of the ocean.

But in 2020, a team of scientists described microbes deep beneath the seafloor that might just be, you know, a lot older than any of those. And this discovery might provide a clue about just how slow life can go. The team wanted to see if they could find life in one of the most inhospitable, inaccessible places on Earth.

They travelled to the South Pacific Gyre, an area of the ocean with so few nutrients, it's been called an oceanic desert. They used a research ship with a giant drill on the back to take samples of clay that had been deposited on the seafloor 101.5 million years ago and have been buried ever since. Back in the lab, they added nutrients to the ancient clay, and communities of bacteria bloomed into life.

These are, by far, the oldest communities of microbes ever found. We don't know exactly how old each individual cell is, so we can't yet tell how many generations of cells lived over the hundred million years they were buried. But as a community, these microbes are clearly ancient.

The team went to great lengths to make sure they didn't accidentally contaminate the sample, ensuring these microbes were really from millions of years ago, and not more recent interlopers. They even added a specific chemical to the fluid used for drilling, so that they could detect it in the samples if contamination had snuck in that way. They also took a very close look at the layers of sediment above the deepest samples, and determined that those layers were pretty impermeable.

Which means the microbes were likely trapped in the sediment the entire time and didn't flow in later. So that means that they've been buried deep, for a hundred million years, with hardly any access to nutrients. How are these things even alive?

One possibility is that the microbes formed spores, a life cycle stage designed to withstand harsh conditions. But only 2.5% of the oldest bacteria the researchers found were even capable of forming spores. So that's probably not the answer.

In this case, the microbes likely slowed their metabolism down to the bare minimum in order to survive. Cells need a minimum level of power in order to stay active. A human body at rest uses the equivalent of roughly a hundred Watts of power, energy generated from the food we eat and the oxygen we breathe.

But these single-celled organisms buried beneath the seafloor appear to need much less. Another study calculated microbes in this environment would need mere zepto Watts per cell. That's a metric prefix indicating a decimal followed by twenty zeroes.

By slowly consuming the tiny amount of oxygen and nutrients available around them, the microbes were able to meet this requirement and hang out for all those years. This discovery could expand the search for life on other planets. It's possible alien microbes could live in similar environments where they were buried long, long ago.

But back here on Earth, the question seems to be: where can't we find life? Hundred million year old microbes are pretty bizarre. And if you like bizarre organisms, Complexly has a whole channel for you.

It's called Bizarre Beasts. Once a month, hosts Sarah Suta and I introduce you to a new bizarre beast and explore what makes these animals so weird to us. From birds whose babies have claws on their wings, to lizards with glowing bones, the show examines the how and why of some of the world's most amazingly strange critters.

And if you want to take a bizarre beast home, check out the Bizarre Beasts pin club! The links for the channel and the pin club are in the description below! [♪ OUTRO].