Let’s learn about some of the oldest life ever discovered!

Further reading:

Microbiologists Find Living Microbes in 2-Billion-Year-Old Rock

Chart of life extended by nearly 1.5 billion years

Show transcript:

Back in episode 168 we talked about the longest-lived organisms known, and finished the episode by discussing endoliths. I’ll quote from that episode as a refresher.

An endolith isn’t a particular animal or even a group of related animals. An endolith is an organism that lives inside a rock or other rock-like substance, such as coral. Some are fungi, some lichens, some amoebas, some bacteria, and various other organisms, many of them single-celled and all of them very small if not microscopic. Some live in tiny cracks in a rock, some live in porous rocks that have space between grains of mineral, some bore into the rock. Many are considered extremophiles, living in rocks inside Antarctic permafrost, at the tops of the highest mountains, in the abyssal depths of the oceans, and at least two miles, or 3 km, below the earth’s surface.

Various endoliths eat different minerals, including potassium, sulfur, and iron. Some endoliths even eat other endoliths. We don’t know a whole lot about them, but studies of endoliths found in soil deep beneath the ocean’s floor suggest that they grow extremely slowly. Like, from one generation to the next could be as long as 10,000 years, with the oldest endoliths potentially being millions of years old—even as old as the sediment itself, which dates to 100 million years old.

That episode was almost five years ago, and in October of 2024 some new information was published. The study mentions the 100-million-year-old limit known so far, where living microorganisms were indeed discovered in geological layers below the ocean floor. But what they found was even older.

The scientific team analyzed rock samples from northeastern South Africa, specifically rock that formed when magma cooled below the surface of the earth. It’s called the Bushveld Igneous Complex and is very large, very old, and very stable.

The team drilled core samples of the rock from 50 feet down, or 15 meters, and cut it into thin slices to examine. To their surprise, they discovered microbial life in the rock’s cracks, which were sealed tightly with clay so that nothing should be able to get in or out of the rocks. To be sure the microbes hadn’t been introduced during the drilling or preparing process, they used infrared spectroscopy to compare the proteins in the microbes with the proteins caught in the clay. They matched, meaning the microbes had been there as long as the clay had been there, which was basically almost as long as the rocks had been in place. They were also able to verify that yes, the microbes were definitely alive.

So, how old are the rocks? TWO BILLION YEARS OLD. Billion with a B! While the individual microbes probably aren’t actually that old, the population of microbes has been living in those cracks far within the rock for two billion years. Scientists are excited to learn more about them, because by studying organisms that have been separated from all other life for that long, they can learn about how early life on earth evolved.

Even more exciting, at least if you’re me, NASA’s Perseverance rover on Mars is going to be bringing some rocks back to earth that are about 2 billion years old. Scientists are really excited to see if there is any evidence for microbial life inside the Martian rocks!

I know I won’t live long enough to see the first macrobial life from another planet, but I really hope I’m alive when we discover the first microbial life. I don’t think life is rare on other planets, it’s just that the distances are so enormous that getting to another planet and sending information back home is an almost insurmountable problem right now. The closest planets to us are Mars and Venus, and these days Mars just doesn’t seem like it would be very habitable for anything but microbes. But microbes can live just about anywhere!

Also in 2024, a team from Virginia Tech has put together a chart marking when various life forms started appearing in the fossil record and when they also stopped appearing in the fossil record. Versions of this chart of life have been made before, but they typically only go back to about half a billion years ago, around the time of the Cambrian. Before that, life was much less likely to fossilize, or the rocks containing the fossils have been worn away.

The team gathered fossil data from scientists and institutions around the world and compiled it into a chart of life that extends back two billion years. The farther back you look, the less changes there are among the type and differences in species. There’s even a huge stretch of time called the boring billion where things really weren’t changing much at all, at least not according to the fossil record we have available. It wasn’t until the earth’s climate became much cooler and then warmed again, between 720 and 635 million years ago, that things really began to change.

The team is considering factors that contributed to the stability of the boring billion, and why it all changed so radically. It’s a good thing it did from our perspective, since if the boring billion had continued over the next billion years until today, we’d all be single-celled organisms. I wonder if the microbes in those two billion year old rocks even noticed the changes. Probably not. They were in rocks.

Thanks for your support, and thanks for listening!