(uplifting music) - I am in the West Texas desert, but I'm also at the bottom of the sea.

That mountain behind me is actually a prehistoric ocean reef built from the bodies of trillions of creatures who once swam in an ancient sea that covered these lands.

Things like ammonoids, brachiopods, and trilobites.

Most of the creatures whose bodies built that reef went extinct more than 250 million years ago in the largest and deadliest mass extinction our planet has ever seen, an extinction we call the Great Dying.

But the fossils they left behind can tell us what our planet was like before that extinction.

Join me as we journey up to the top of that mountain and back in time, hunting for the fossils of those strange, ancient, extinct creatures.

Why?

Because what we find here might tell us about an extinction event we could be on the brink of today.

(uplifting music) All right, we're about two hours from El Paso and a solid day's drive from the nearest coastline, but we are about to climb a reef.

This is not a coral reef, not like you're imagining.

This reef was slowly built from the calcified remains of sea creatures, and it is massive.

(pensive music) During the Permian period, this reef extended hundreds of miles from Texas into what's New Mexico today.

It's one of the best preserved ancient reef systems on Earth and one of the best places for researchers to understand what was going on in the Permian.

- We're walking up a mountain, right?

But you have to imagine there's like 2,000 feet of water be over our heads right now.

- [Joe] Dustin Sweet is our guide into the past.

He spent a lot of time in these mountains investigating the geologic fingerprints of the Permian period.

Back in the time of Pangaea, this piece of land was actually near the equator, and the warm water was home to a multitude of what were likely very colorful sea creatures.

Down at the base of the slope, a cakey layer of limestone is a marker of how rocks play a very important role in balancing Earth's climate.

- We're looking at pelagic limestone, which is important for our long-term carbon storage.

The carbon comes from CO2 in the atmosphere, which then gets moved to the ocean and it turns into a calcium carbonate crystal, either through seashells or as little tiny microparticles.

- And through a lot of time and waiting, it becomes this?

- Yeah, it settles down through the ocean.

These 2,000 feet of water that's above it settles down to the ocean floor and becomes a rock.

- Wow.

(pensive music) There's a couple more miles to go before we reach the reef.

It's time to put some trail under our feet.

(rocks clattering) - Oh, here we are at the base of the reef, and okay, look.

There's sponges just everywhere.

See these guys right here?

- [Joe] Wow.

- [Dustin] They attached up here.

Come down, you see their chambers.

- [Joe] There's so much detail preserved in these.

This one, you can still feel the texture of its body.

- They look like sponges, but they're not the sponges we see today.

These all went extinct at the Permian-Triassic boundary.

(pensive music) - [Joe] Traversing this path is like walking through an ancient cemetery.

At the end of the Permian, these ancient sponges went extinct, as did many more creatures, the fusulinids, some bivalves, nearly every brachiopod, and every type of algae that was once here on this reef.

Why did so many species meet their demise at the same time?

What was the cause of the Great Dying?

By the end of the Permian, almost all life on Earth ceased to exist.

Somewhere between 80 to 96% of animal groups went extinct.

There was no single cataclysmic event that triggered the Great Dying.

No terrifying asteroid, like the one that extinguished the dinosaurs.

The Permian came to a close due to a phenomenon we are all too familiar with: massive global warming triggered by atmospheric change.

The first ingredient in the recipe for the end of the Permian times were the volcanoes.

Not big eruptions, like you might imagine.

The Permian was host to the so-called Siberian Traps in what is today Eastern Russia.

Over a period of nearly 2 million years, a massive volcanic region, about 5 million square kilometers, nearly half the size of China, slowly seeped lava, ash, and gases, like carbon dioxide and sulfur dioxide.

When the plants started to die off, so too went the herbivores, and after them, the carnivores.

It's thought that about 70% of terrestrial animals died off during that time.

Creatures like reptiles, amphibians, and the big saber-toothed monstrosity that I'm glad I never had to meet in a dark alley.

Meanwhile, the oceans got busy absorbing the masses of CO2 in the atmosphere, as they still do today.

Oceans take up as much of 1/3 of the carbon dioxide we release.

And near the end of the Permian, that led to extreme ocean acidification.

One recent study suggests that planetary weather cycles, similar to today's El Nino, caused ocean temperatures to increase dramatically.

Marine life just could not catch a break.

To understand what life looked like before all this turmoil, we need to visit that ancient sea, and we're finally almost there.

(rocks clattering) We made it.

- [Dustin] We made it to the top.

- [Joe] Wow.

- [Dustin] Look at that canyon.

- [Joe] That's beautiful.

- [Dustin] Below that's the reef.

Look at how steep that is.

Imagine mountain line climbing up and down in that.

- They're meant for it, though.

- [Dustin] Yeah.

- I don't know if we are.

- We are not.

Well, I'm always amazed up here.

The view's great and I'm just out looking at rocks.

It's wonderful.

I've been up here probably around 20 times, and every time, it's amazing walking up that slope to think that you're walking up a slope that existed 270 million years ago.

To me, that's fascinating.

- It's been an incredible journey back in time.

Completely new perspective on Earth's history, but we've got quite a journey to go to get back down to the bottom.

So, I say we get moving.

- Let's do it.

(pensive music) - Scientists agree that Earth has seen five mass extinction events in its history, with the end Permian being the worst.

Some believe we could be on the cusp of a sixth today.

Biodiversity is declining faster than at any point in human history.

The impacts that humans have had on planet Earth in the last five to six decades are like nothing that we've seen in at least the last tens of thousands of years, perhaps even longer.

Atmospheric changes, in particular, are happening in order of magnitude faster than anything that researchers have seen in the geologic record.

What we have been able to understand about the vast expanse of time that stretches out behind us is astonishing.

That knowledge grows every day, and with that knowledge can come change.

The creatures that perished in the Great Dying, they didn't have that knowledge.

They didn't have a choice.

But we do.

So perhaps the question we should be asking ourselves is: What mark do we want to leave on a future Earth?

(pensive music) (wind whooshing)