Once upon a time…by which I mean  roughly two billion years ago… some bacteria wiggled their way into  a tiny crack in the surface of a rock.

But eventually, a bunch of clay plugged  up the entrance to that little cave of theirs, trapping them inside and  isolating them from the rest of the world. The colony missed out on witnessing  the rise of complex multicellular life, Earth’s whole dinosaur phase,  and that Roman Empire people can’t stop thinking about.

But it did not die. Then a few years ago, a team of scientists came along and cut that rock open. Humanity had found the oldest  living thing, by, like, a lot.

And their discovery raises questions  about how life might survive not just in some of the most  isolated places on Earth, but beyond. [♪ INTRO] In 2010, a group of scientists set off  on a journey through the South Pacific. And they used a set of massive  drills to collect chunks of the Earth’s oceanic crust up to  125 meters below the seafloor. Once the rock samples got to the  lab, researchers then cut them into thin slices, and peered at them  through high-powered microscopes.

It turns out, these rocks had a  bunch of teeny tiny fissures in them. And I’m talking less than a millimeter wide. And they were packed full of not  just sediment, but living bacteria.

This was not the 2  billion-year-old bacteria colony. We’re gonna get to that part soon. Now, finding bacteria inside rocks  isn’t really a huge surprise.

Bacteria live just about everywhere. But this particular find was noteworthy because some of these rocks were  about 100 million years old. And those microscopic fissures appear  to have been completely sealed off from the outside world…at  least before the scientists had cracked the samples open.

So those bacterial colonies would  have been living inside their rocky abode for at least, like,  90 of those 100 million years. Understandably, the researchers were skeptical. After all, it’s possible the bacteria had somehow snuck in there more recently.

They could even have been introduced accidentally during the drilling process. But the team had good reasons  to think that hadn’t happened. For one thing, the fluids that  are used in the drilling process have particular chemicals in  them, and the researchers found no trace of those chemicals inside the fissures.

Plus, before they cut open the  rock samples, they had removed any outside hitchhikers by cleaning the  samples, and setting them on fire. In a controlled, scientific way, of course But just to make sure, they also  compared these fissure microbes with samples from the nearby seafloor,  and with other drilled samples that were known to be contaminated  with outside microbes. The signs all point to the same  answer: the bacterial colonies inside those rocks showed no signs of recent  contact with the outside world.

They really were that old. So when this research was published in 2020, it held the record for the oldest  rocks known to harbor living things. But a few years later, in 2024,  the same team of scientists announced that they had broken their own record.

By 1.9 billion years. This SciShow video is supported by  SciShow’s favorite band: ÉKLEIPSIS. This band is so good, the only word you can use to describe them is ‘unreal.’ After their Path Of Totality Tour last  April, ÉKLEIPSIS returns this year to celebrate the upcoming total  lunar eclipse on March 14th.

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And international orders aren’t  guaranteed to make it before the lunar eclipse, but there is a chance if you’re  watching this video as it comes out. This time, the rock samples came from  the northern part of South Africa. Specifically, a rock formation  called the Bushveld Igneous Complex.

These rocks were created during  the Palaeoproterozoic Era, around 2 billion years ago, when  magma from deep within the Earth seeped up toward the surface,  and then cooled down and solidified before actually  poking above the surface. In geology speak, we call  those intrusive igneous rocks. Because they, well, intrude  on the rocks around them.

And over time, erosion can wear  away the rock on top of them, exposing them all for us to stumble upon. Which leads me to the second  reason why the rock sample was different from the Pacific seafloor samples: These were taken from the  much more convenient depth of 15 meters below the surface. Once again, this research team cut  open their rocks, peeked inside, and found tiny cracks with living microbes.

And also once again, they  tested for outside contamination and found no sign of it. The evidence suggests bacteria  really have been trapped inside this rock formation for nearly  half the history of our planet. That said, it’s important to note  that the individual bacteria that make up the colony are certainly  not billions of years old.

Over time, they would grow old and  give rise to the next generation, just like the cells that make up our bodies. Due to the limited resources at their disposal… because they’re, you know, trapped  inside a microscopic rock fissure… they go through that lifecycle  much more slowly than ours. But yes, the founding bacteria of these  fissure communities are long gone, and the cells that these scientists  discovered are their living descendants.

Their great-great-great-great-great  … well, you get the idea. And the secret to their incredible survival might lie in the makeup of the rocks themselves. Rocks in the Bushveld Igneous  Complex seem to be a good place to sit still for a couple billion years.

For one thing, the area around the complex shows very little evidence of past tectonic activity. And maybe more importantly,  the rock formation itself shows very little sign of movement. There are no major faults  or folds in the rock layers.

That suggests these rocks  have been remarkably stable. They’re basically unchanged  from the time they formed. And if you’re a bacterial colony  looking to live in the same house for 2 billion years, you want a stable house.

But in addition to that  structural support, the fissures are partially filled with clay minerals. And some of those minerals, like  iron-rich smectite, are good at collecting organic compounds that  certain microbes can then feed on. The research team hasn’t published any genetic tests on their 2  billion year old bacteria, yet.

But their 100 million year old  samples resemble some modern microbes that rely on methane and other organic  molecules to fuel their metabolism. It’s likely their much older cousins  make their living in a similar way. And these bacteria aren’t just  surviving, they’re thriving!

In deep seafloor mud, you can typically find about 100 bacterial cells in every cubic centimeter. But in the 100-million-year-old  ocean crust samples, the team counted about 10 billion  cells per cubic centimeter. That’s similar to the density  of microbes inside our guts!

So, it seems the same sediments  that filled in the cracks and sealed these bacteria away  are also a great source of food. It’s like a well-stocked bunker for surviving not just one apocalypse, but many. Because in the past 2 billion  years, Earth has gone through, like, at least five separate mass extinctions.

Speaking of surviving, this discovery  has scientists wondering just how many microbes are eking out an existence in other subterranean environments. And if these habitats are more  friendly to life than we realized, it might have consequences for life beyond Earth. The mineral content of these ancient rocks… as well as the cold temperatures  in places like the deep ocean… are pretty similar to conditions on,  or at least near the surface of Mars.

So, in our ongoing search for Martian microbes, rock formations like these might be  great places to take a closer look. Two billion years ago, Mars’s  surface had already transitioned from a water-covered world  into a desolate wasteland. But microbial life has existed on  Earth for over 3.5 billion years.

So maybe…just maybe… And personally, I think I’d rather be  a Martian microbe trapped in a rock for more than three billion years. Because given the history of life on Mars, there’s a lot less I would have missed out on. [♪ OUTRO]