Original subtitles

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Yellowstone National Park

stretches over nearly 3,500 square miles

of spectacular wilderness.

Wyoming, Montana, and Idaho all claim shares

in the dramatic vistas and charismatic wildlife.

The landscape that we see here

is formed by numerous geologic processes,

spanning all the way back to 3 billion years old.

Greater Yellowstone

sits on top of a volcanic hotspot

where devastating geological events unfolded.

We had kind of three major caldera forming eruptions,

big explosive events, leading up to today.

Here we have kind of a series of volcano classic deposits,

a bunch of different kind of individual volcanic rocks.

The prehistoric upheaval

created a bizarre cemetery on Specimen Ridge

and around Tom Miner Basin.

These dead trees are made of stone.

The Gallatin Petrified Forest is a series of forests

that were buried in volcanic debris flows.

We have these layers and layers of forest.

Thanks to the volcanism,

a big mudslide come in, burying the forest.

And then you have a new forest growing for maybe

a few hundred to a thousand years.

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(birds chirping)

Greater Yellowstone's fossilized forests

contain the remains of trees that died from molten lava,

ash, and mud around 50 million years ago.

The tremendous heat melted snow on the mountains

sending deadly mudslides rushing down the slopes,

burying everything in their path.

That will go down like a river channel

and anything that's in that channel,

will just be inundated with all that material.

Dr. Madison Myers

is a Volcanologist at Montana State University.

Stumps, leaves, and even pollen

were all preserved in the volcanic slides,

resulting in a unique record of life during the Eocene.

This was the warmest time period since the dinosaurs died.

We had no ice caps at the poles.

In Wyoming, you had this very warm, temperate,

to even tropical climate.

It supported palm trees, it supportive crocodiles,

alligators, turtles, all these things

that you just could not even imagine here today.

Dr. Ellen Currano

from the University of Wyoming,

uses fossil plants to investigate ancient forest ecosystems.

One of the coolest things about plant fossils

is that you can use them to interpret what climate was like.

If you can just identify the fossil and you know what it is,

if it's something that is around today

or maybe something closely related is around today,

we can look at where does that species live today?

(footsteps crunching) (insects buzzing)

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The Gallatin Petrified Forest

was just a normal forest,

but you can imagine it being a forest at the flanks

or at the base of a volcanic system.

So for instance, thinking of Mount St. Helens

and that eruption and all those trees that were then buried

or knocked over by flows that were coming off of it

during the eruption,

similarly, the Gallatin Petrified Forest was buried

by repeated material coming off of these volcanoes.

It wasn't a one time event.

The area's volcanoes erupted continuously

for millions of years.

Yellowstone's Petrified Forest

actually contains the remains of 27 separate forests,

each stacked on top of the other, layer by layer.

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(birds chirping)

It is so much bigger

than almost any other petrified forest we know.

14, 15, 16, 17, 18, 19, 20.

Okay, that's 20 years right there.

So that kind of gives you an impression

of how old this tree was.

(birds chirping)

And it's bigger in a couple dimensions,

most notably the up and down direction.

No other place in the world

boasts a comparable record.

One interesting feature

of the petrified forests around Yellowstone

is the strange absence of diagonal or leaning trees.

You could understand something

about the intensity of that degree flow

by looking at how much of it has been kind of knocked down.

You would have to understand something about the strength

of the trees.

Here at Yellowstone,

you have that forest being buried in place,

20 plus times.

Despite detailed studies

over the last 100 years, no animal fossils have been found.

Plant material is actually preserved

more readily than animal material in these things.

And I think part of that is because

animals have the ability to move and run away if a flow,

if they hear that and feel that rumbling

of something coming towards them,

whereas you don't have the ability if you're a tree to move.

So it's actually pretty rare to find plants and animals

in exactly the same layers.

(birds chirping) (soft relaxing music)

Fossilized plant material

gives us a more accurate snapshot

of the prehistoric climate in this region.

I use leaves to interpret climate

and, specifically, leaves from flowering plants.

So think of something like a magnolia

versus something like an elm or a beech.

If you go to the Southern U.S.,

you see a lot of things like magnolias and dogwoods,

whereas if we're up in more Northern climates,

so you've got oaks and maples.

So we have this modern relationship

between the temperature in which a forest grows

and then we apply that same thing in the past.

Over 150 species

of fossil plants from Yellowstone

have now been described,

but it's the big trees that draw the most attention.

Some of the trees appear to be preserved

in their original positions

while others may have been transported by mud or water.

But if you see a bunch of trees

that don't seem to be knocked over within the flow,

it's either that the impact of the flow

wasn't high enough to knock them over

or that they were on a more level piece of ground.

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There is evidence

that some of the petrified wood was transported.

So for instance, in Tom Miner Basin,

you can see, like, stumps of trees

that are at all different angles and different sizes

that seem to suggest that they may have been transported.

However, there are other areas in the petrified forest

that trees seem to be largely upright still,

and preserved in-situ that way.

So I think both processes likely were happening

that you had some that were transported

in flows that were high enough energy or small enough trees,

whereas others were just kind of covered by the material

that were coming off of these volcanoes.

After each eruption and damage to the forest,

the resilient trees began to grow again.

But the forests were very different 50 million years ago.

Yellowstone's Petrified Forest

isn't the only fossil forest in the world,

but it is unique because of how the trees were preserved.

The petrified forest here

is different from the one that's located in Arizona,

mostly by the process which formed the petrified wood.

They both involve volcanic systems,

but the way in which they were buried,

in which the solidification process occurred,

are different processes.

So here the petrified forest was formed

through debris flows coming off of the Absaroka Range,

burying the material in these kind of thick,

really large, cobbly, volcanic material.

So some of them were standing,

some of them were knocked down,

and then silification occurred.

In other ancient grooves,

minerals completely replaced

every part of the trees over time.

But in Yellowstone, the original organic matter

and actual cells of the wood

have been preserved within the minerals.

Yellowstone is this amazing volcanic system

and we have that to thank

for the incredible preservation of these fossil forests.

So we have this amazing source of silica all around

and then, you have the hydrothermal activity.

(water splashing)

Super-heated water is traveling through the rock.

It's dissolving out some of the silica

and then that silica-rich, really hot water,

is permeating the wood.

And so as it does that, it starts cooling

and silica starts precipitating out

in the empty pore space in the wood.

And so in a lot of petrified wood

it's just straight up silica,

but the way things worked here with the volcanism

and with the hydrothermal activity,

you have the silica precipitating out inside of the cells

and a lot of that organic material

then remaining in the cell wall.

And it's been cutoff from oxygen,

from bacteria that are gonna decay it.

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Most of the fossil trees

in Yellowstone are redwoods.

Redwoods are some of the

fastest growing trees on Earth.

In good growing conditions, so lots of water,

enough nutrients, good CO2,

a redwood can grow something between two

and even as much as eight feet per year.

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Today, redwoods

don't grow in Greater Yellowstone.

The region is now classified as subalpine,

but Ellen can tell from fossil leaves

that Yellowstone once enjoyed a subtropical climate.

A well-preserved leaf looks like

it just fell off of the tree

and you can see every single detail,

the outline of the leaf, the veins,

every tiny little bit of venetian on that leaf.

And you know, they're just gorgeous.

(footsteps crunching)

50 million years ago here in the greater Yellowstone area,

the mean annual temperature would have been something like

70 degrees Fahrenheit.

(rain splashing)

The area probably received

50 to 60 inches of rain each year.

Like any forest, living or fossilized,

insects play a key role

in the health of the trees and plants.

That's a big one.

Let's say that an insect chews a hole in a leaf.

The leaf can't repair itself,

it's not gonna grow new tissue to fill in that hole.

But what it's gonna do is it's gonna make

a thickened rim of tissue around where that damage occurred.

So looking at damage can tell us

something about insect diversity.

And this is something that can be really interesting

during times of changing climates.

As CO2 levels increase,

plants actually become less nutritious.

Average temperatures in the park

are higher now than they were 50 years ago,

especially during springtime.

And nighttime temperatures are increasing more rapidly

than daytime temperatures.

We may be headed back to the Eocene.

(birds chirping)

Peak warming was between about

53 and 51 million years ago.

And, fun fact, if we continue burning fossil fuels,

by the year 2140, Earth's climate will be a lot more similar

to that peak warming than it is to today's climate.

(waterfall splashing)

The investigation

into Yellowstone's mysterious Petrified Forest

will continue for a long time.

The scientists hope to use their discoveries

to help to predict what the rapidly changing climate

might mean for Yellowstone in the future.

The fossil record gives us this opportunity

to see how ecosystems are changing

in response to climate change,

both the temperature and the carbon dioxide levels.

We always are studying past climate to try to understand

something about future climate, for sure.

(birds chirping)

Yellowstone's fossil forests

provide geologists with a window to the past

that may be a critical window into our future.

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