Name: 超级火山是如何使新生代最酷的化石形成的（How a Supervolcano Made the Cenozoic’s Coolest Fossils）
Uploaded: 2021-05-01T10:06:48.000Z
Duration: 9 min 39 s
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One day, about 12 million years ago in the heart of North America, herds of rhinos were

grazing on wide-open grasslands, while turtles swam in a nearby watering hole.

Early dogs hunted in the underbrush, and long-legged cranes searched the water for food.

I like to think that it started out as a nice day.

The air quickly filled with volcanic ash, dimming the sky and falling to the ground

in clumps, forming drifts like snowbanks.

The ash coated everything, including the plants the animals  ate, causing their teeth to

become scratched and worn as if they'd been chewing mouthfuls of sand.

And they unavoidably inhaled it - the sharp, glassy edges slicing at their lungs.

After days or weeks of suffering, the rhinos and other animals eventually succumbed, and

The watering hole where that took place is now known as the Ashfall Fossil Beds  in...

Yes, Nebraska -- where there are no volcanoes within a thousand kilometers.

So what caused this really bad day in the Miocene?

The answer rests inside one of the most dynamic, transformative, and potentially dangerous

features in North America, a feature that's also responsible for some of the continent's

The Yellowstone volcano is actually a supervolcano.

That means it's more explosive than your run of the mill volcano, and the effects of

One of its eruptions, 2.1 million years ago, was about 6,000 times as big as the eruption

Today, Yellowstone slumbers beneath the ground in Wyoming.

But 12 million years ago, it was in Idaho.

And 16 to 14 million years ago, it was on the border of Oregon, Idaho and Nevada, making

a brief stop in its long, slow migration across the continent.

The volcano itself isn't actually moving.

Instead, it's fed by a mantle plume – a massive body of magma that originates deep

inside the earth before upwelling toward the crust.

That plume holds relatively still, while the continent above moves over it.

Geologists refer to the volcanoes and craters made by these-plumes as hotspots.

As North America is slowly pushed across the Yellowstone plume by plate tectonics, it creates

a string of volcanic scars above where the plume once was.

And no matter where it's been, every few hundred-thousand years, the supervolcano erupts,

churning out remarkable amounts of lava and ash.

But, as big and impressive and even destructive as those eruptions have been, none of them

have actually caused any major extinction events.

In fact, for paleontologists, what makes the Yellowstone plume so special is not just the

magnitude of its eruptions – it's the fact that those eruptions have turned out

to be really, really good at preserving fossils.

After all, lava plus animals equals, well… fire and burning.

Unless you're Chris Pratt, in which case you're somehow just fine.

So how can something like that be responsible for saving fossils rather than destroying

Well, let's talk about those Nebraskan animals first, because not only are they amazing,

it's also where I did my undergraduate summer internship back in 2006.

Now 12 million years ago, the Yellowstone mantle plume was under Idaho, and the volcano

there erupted, sending ash flying 1600 kilometers away, probably reaching as far as the Atlantic

The ash killed and buried the animals, preserving them at Ashfall Fossil Beds in faraway Nebraska,

creating the only fossil formation made entirely of falling ash.

And although the event sounds sudden, the process at Ashfall was painfully slow for

When the ash started to fall, smaller animals, with their smaller lungs, were quickly overwhelmed

This is why the bottom of the Ashfall fossil beds contains a layer of small animals, like

Their remains were then trampled on and scavenged, as other larger, hardier animals continued

And next came a layer of medium-sized animals, including horses and small camels.

They would've survived longer than the turtles and birds – for weeks, rather than for hours

As a result, the skeletons of  these animals show signs of bony growths, which are caused

An affliction known today as “Marie's Disease”.

Then, on top of all this, is a layer of more than 100 individuals of the rhino species called

Being bigger than all the other animals, the rhinos were able to live longer.

Their remains, too, show evidence of Marie's Disease, and they may have lasted weeks or

even months, only to finally succumb to fever, pain, and irreversible lung damage.

Now, as painful as they were, the deaths of these animals were still scientifically invaluable.

Ashfall preserved so many articulated rhino skeletons that scientists are now able to

tell males from females – males were larger had bigger lower tusks

And the way the rhinos were preserved even taught us a lot about their behavior.

Because their skeletons were found together and mostly uncrushed, it seems that the rhinos

That herd was made mostly of juveniles and adult femalestheir mothers, some of whom were

There were only a few males in the formation, which suggests that there probably weren't

Now, some modern rhinos form herds, but their herds are typically about a tenth the size

And that sort of knowledge about herd structure is almost impossible to get in the fossil

record, because it requires that a lot of animals die together, and very quickly.

Otherwise, it's hard to say if animals died in a group, or if lots of solitary animals

But it's not only volcanic ash that can preserve amazing fossils.

14 million years ago, lava from the Yellowstone Plume coursed through what's now Washington

And while lava normally burns soft tissue - as anyone who's played “the floor is

lava” will know - this lava was cooled enough by the water that it left a particularly brilliant

Lava spilled down into a lake and covered a dead, bloated rhino called Diceratherium,

which was either on the shore of the lake or was already floating in the water.

And remarkably, the lava cooled so quickly that the rhino became entombed in rock – still