Most of us would look at this rock and think that it’s just an ordinary rock.

This is epidote, and while sure, it looks pretty, it doesn’t seem all that special at first glance. But epidote has a secret.

This mineral could reveal  the origin of life on Earth. And it might help us find  life on other planets, too. [ INTRO SONG] Epidote is a prismatic mineral that has a silicon dioxide scaffold, interspersed with aluminum and iron in varying quantities, which can give it a really lovely pistachio-green color. When the crystals are nice and big, it can be used as a gemstone, but it’s not the toughest of minerals, so it doesn’t stand up to much wear and tear.

Instead, it’s much more useful  to geologists who are studying   past environments and looking for the places  where ancient life forms would have hung out. And to explain how all that works, let’s go way back to the beginning and talk about the early fossil record, which goes from microbes, to trilobites, to dinosaurs, to us. Obviously it didn’t happen exactly like that, but you get the picture!

The problem is, the further back in time you go, the harder it is to interpret just what it is you’re even looking at in these old rocks. Because plate tectonics do a really good job of  recycling older rock layers, including the ones with all those fossils from life’s early history. And even if those fossil-bearing  rock layers do survive, both the rocks and the fossils in them tend to get more messed up the longer they’ve been hanging around on the surface.

Since the earliest lifeforms  were probably small, squishy, and weird-looking, that makes understanding what was going on in the early days difficult, to say the least. Paleontologists are pretty sure that the first life forms would have been things like bacteria that lived at least three billion years ago, but there’s still a lot that they don’t know. For instance, we don’t know what kinds of environments were hospitable for life back then, or how early living things got the energy and nutrition they needed to survive.

Which means we may not even know what the first fossils or chemical signs of life will look like if we do find them. But researchers tackling these questions using modern lifeforms have found a surprising clue to at least part of that puzzle. Looking at the genes shared by some of the simplest organisms alive today, it appears that the earliest microbial life forms were equipped to deal with some extremely hot conditions.

And that’s where epidote comes in! When some minerals like feldspars get exposed to moderately high  temperatures or pressures, or get exposed to really hot liquids, those feldspars are hydrothermally altered into epidote. Hydrothermal alteration happens in the Earth’s crust wherever fluids interact with rocks in hot environments, like near underwater ocean ridges and at subducting plate boundaries.

Seawater penetrates through cracks in the rock, gets heated by magma beneath the surface, and then shoots back up. The escaping fluid brings minerals with it, which creates underwater chimneys and spews out what look like plumes of smoke, in what are fittingly called ‘black smokers’. Despite being scaldingly hot, these black smokers and other hydrothermal systems are ideal for biodiversity in the deep ocean.

The heat, minerals, and water all form the basis of a unique kind of ecosystem that attracts tons of weird sea critters. And paleontologists think that billions of years ago, early life forms would have loved to hang out around these vents too. So if we find ancient hydrothermal vents, we find places that are more likely to have fossils of early critters.

Lucky for us, we can look for this pretty pistachio mineral as an indicator of where hydrothermal systems existed in the past. Geologists can just look for its characteristic green color following cracks and veins in volcanic rocks to see where the hot, mineral-rich fluids once flowed. Like in the Pilbara region  of northwestern Australia, which is host to some of the  oldest rocks in the world.

These rocks date to roughly 3.5 billion years ago, and they’ve yielded some of the earliest fossils called stromatolites, which are made up of layers and layers of simple, bacteria-like cells. And in order to learn more, geologists looked for concentrated  veins of epidotized rocks to hone in on some of those hydrothermal systems. They drilled through the layers  of 3.5 billion year old rock and found both epidotized volcanic rocks, and layers of carbonates and silica-rich cherts, which would have formed on the ancient sea floor.

And all of those rocks can tell us about the ocean chemistry way back then. They could reveal the types of early ecosystems that were there too, and could even give us hints about how those organisms’ metabolisms worked. This information can help build a picture of how the earliest life survived in these extreme environments on Earth.

And speaking of extreme environments epidote might also be helpful in the search for life on other worlds, too. One of our biggest questions about the universe is whether life has existed on other planets, and thus one of the biggest questions about Mars is whether life has ever existed there And Since epidotization can be a signature for ancient hydrothermal systems, and by extension ancient extreme habitats, rovers on Mars are keeping an eye out for epidote as a proxy for those once-habitable environments. So far, Spirit and Opportunity have detected tiny amounts of epidote on Mars.

Not enough to say there were hydrothermal vents, but enough to pique our interest. So it’s definitely something that researchers are looking out for in future Mars missions. Which means the secrets to the origins of  life on at least two planets, might all connect back to this pretty, and pretty ordinary looking little rock.

Luckily for us, we didn’t have to go all the way to the ocean floor or to Mars to get our Rocks Box subscribers some really gorgeous pieces of epidote. Every month, subscribers get that  month’s mineral or fossil specimen, along with an info card telling  you all about why it’s so cool. You may have noticed that it’s not easy To get into the Rocks Box subscription We are constantly sold out We have some right now I think  that you can subscribe to The rocks are always ethically sourced, and we keep subscriptions low to ensure that everyone gets high-quality pieces.

Head over to SciShow.rocks  now if you’re interested – the spots fill up fast. I’m sorry if you don’t get in Thank you as always, for watching [Outro]