Hey everyone.

My name is Chris Anderson, and I'm at Grand Canyon National Park!

Here, the Colorado River has carved a gorge more than a mile deep, in some places up to 18 miles wide, and exposing rocks almost 2 billion years old.

That's nearly half the age of the planet.

So what can we learn about Earth's history from one of the continent's most iconic landscapes?

Let's find out today on OutSCider Classroom!

[Intro Music] [Music] Just like ogres, onions and parfaits, the earth has layers.

These layers are formed over millions of years as sediments like mud or sand are deposited and slowly become rock after a lot of time, heat and pressure.

But unlike ogres, onions and parfaits, the Earth's layers tell a story.

And just like any good book, once you learn how to read those layers, you can be transported to another world.

You can learn what the earth was like millions of years ago just by looking at the rocks.

So how do you learn how to read rocks?

Let's start with four simple rules.

Rule number one: younger layers are on top of older layers.

This makes a lot of sense.

If you were to say make a sandwich, you start with some bread, then put some mustard on, then some cheese, maybe a tomato or some deli meat or whatever else you want on your sandwich, then your top layer of bread.

The first layer of your sandwich would be at the bottom, with the most recent layer being at the top.

Rocks are the same way.

Oldest layers at the bottom with younger and younger rocks as you move up the geologic column.

This layer.

Then this layer, then this layer, then this layer, then this layer.

Scientists call this the law of superposition, which is really just a fancy way of saying oldest on the bottom, youngest on the top.

This rule is really useful because you can tell how old something is based on where it is in a rock column.

Then this layer, then this layer, then this layer.

If you were to take a hike into Grand Canyon, the youngest layers of rock would be at the top.

Then you'd gradually walk back in time until you got to the bottom of the canyon, where you'd find the oldest rock layers.

Nearly 2 billion years old.

Crazy for rules two and three.

Let's check in with paleontologist Gabe Santos.

This layer, then this layer, then this layer.

Then this layer.

Thanks, Chris.

The next law is the law of original horizontality.

In geology, we look at rocks like layers through time.

At the very bottom, you have the oldest layers, and all the layers on top are much younger.

Each of these layers was deposited flat because as new rocks and sediment are brought in, gravity causes them to lay one right on top of another.

Think of it as like making a sandwich, and each of those layers are placed on the countertop flat, and if you pick it up, you can kind of change its shape.

That's kind of how layers work in geology.

There are forces in the Earth that can cause all these layers to change shape.

Sometimes forces might cause them to bend into a U shape.

Sometimes forces can cause layers to uplift and change.

They can get them to scrunch.

And in very rare cases, sometimes layers can be completely flipped.

So the next law is the law of cross-cutting relationships.

What this means is that all of the rock layers are older than anything that happens to them.

So let's think about our sandwich again.

You've got your sandwich made on your countertop, and it must be made before you can cut it, before you can add something to it or pull anything out.

So in geology, when we look at our layers, you've got things like faults and fractures, cracks that run through all the different layers.

You've got intrusions, brand new layers of rock that come in and replace or break through other layers.

You've even got unconformity where whole layers are missing or eroded.

So again, cross-cutting relationships means that all of these rock layers are older than anything that changes or disturbs them.

[crunch] There's one more law that helps us understand how rock layers tell us about Earth's history.

And the Grand Canyon is a great example.

Rule number four says that rock layers are continuous in all directions.

That means the same rocks on either side of the canyon would have been formed at the same time by the same source.

This limestone here on the South Rim and the limestone at the same level on the North Rim, were formed by the same ancient sea 250 million years ago.

Think about it.

If you cut a sandwich in half one side, doesn't rearrange itself, the layers are still in the same pattern.

Scientists call this law of lateral continuity.

And it's really helpful because Earth's surface tends to change a lot.

Understanding how rock layers work is really important because it can give geologists and you evidence for what the earth was like millions of years ago.

You can learn how old rocks and fossils are, what the environment was like, the climate, even what species were around.

You really can travel through time just by remembering four simple rules.

Superposition, original horizontality, cross-cutting relationships, and lateral continuity.

See if you can use these rules to learn about the rocks near you.

You never know when you can learn about the planet in your own backyard.

Then this layer, then this layer, then this layer.

[Music] Grand Canyon isn't just a pretty face.

The exposed rock layers can tell us a lot about what the Earth was like hundreds of millions of years ago.

We can learn what lived there, what the environment was like, and infer the age of the rock.

Come on, let's take a hike.

[Music] Okay, so quick side note we made this video over the course of a couple days because getting to the bottom of Grand Canyon is no joke.

It is a very challenging task.

We do not recommend you hiking to the Colorado River and back to the top in the same day.

If you do hike into the canyon, remember going further down is always an option, but getting back to the top is mandatory.

So know your limits and if you have any questions, ask a park ranger.

Okay, back to science.

So we're about a mile down the trail and you can see these gorgeous sandstone layers.

This rock is about 275 million years old.

When the area where we're at now was covered by giant sand dunes on the coast of an ancient sea.

Spiders, millipedes, scorpions were all cruising this beach, but these weren't your grandfather's arthropods.

These suckers were huge.

There was about 50% more oxygen in the atmosphere back then, which allowed for these monsters to get up to three feet long.

I mean, can you imagine a dragonfly that big coming at you?

That's terrifying!

Unfortunately, since these animals have an exoskeleton and not bones like you and me and dinosaurs, they tend not to fossilize very well.

But what you can't see are trace fossils.

A trace fossil is a burrow, a trail, a footprint.

Evidence that a living thing leaves behind other than its actual remains.

And you can learn a lot about a species just by examining its trace fossils.

By looking at these fossils.

We can begin to imagine what this world was like 275 million years ago.

Big sandy dunes with marshy plants on the coast.

Oh, and meter long spiders and insects.

[screaming] Maybe I don't want to imagine that.

[Upbeat music] Further down the trail, and we go further back in time.

Back to round 335 million years ago.

As you can see behind me, the rocks look totally different.

Instead of sandstone, we see limestone.

That's because instead of a sandy coast, this area was a warm, shallow sea.

Different era, different climate.

Which, you guessed it means a totally different set of fossils.

Here you'd find a bunch of species you'd see if you took a dip in a similar ocean today.

Things like corals or sponges or brachiopods, which make seashells, and bryozoas, which are a type of filter feeder.

But you'd also find a bunch of things that have been extinct for a long time.

Things like, say, trilobites, which looked like little rolly polies, except much bigger.

And they lived in the ocean.

These guys ruled the seas like dinosaurs, ruled the land, except for much longer.

You also might find these little discs in the rock which are actually fossilized crinoids.

These guys looked like a starfish on a stick and would kind of wave around and catch anything that floated by.

They don't exist as much anymore.

But half a billion years ago, the floor of this sea was covered with them.

[Upbeat music] As we go down the trail, something weird happens after this layer of 550 million year old sandstone.

There's a gap in the age of the rocks, and it's not a small one either.

It's over a billion years.

That's like erasing everything from the first multicellular life to today.

That's a long time.

So what the heck happened?

Remember, Earth's surface is always changing.

Wind, rain, heat, living things.

They all work together to break down rocks and the process never really stops.

Eventually, exposed rocks break down and their sediments are carried away by erosion.

And that's likely what happened here at some point in Earth's history.

These layers were exposed to the elements, broke down, and their sediments were carried away, leaving a gap in the rock record.

Scientists call this an unconformity.

When there's a gap in the age of the rocks down here at the bottom of the canyon.

We see the oldest rocks, some of which date from nearly 2 billion with the “B” years ago.

That's way before dinosaurs or fish or anything with the backbone.

This is what we call metamorphic rock.

When the Earth's forces transform existing rock into something new.

Over time, and remember, we're talking almost 2 billion years here, the mudstone and shale that was originally here, was subject to intense heat and pressure.

All of that energy and compression turned that rock into something new.

Schist.

Most life from the time period this rock was formed was unicellular.

Things made up only one cell.

So bacteria and algae.

But that doesn't mean they didn't leave anything behind for us to remember them by.

In some places you can see these ripply waves in the rock.

These are the trace fossils of algae.

They were algae mats of green mats of muck from billions of years ago.

I mean, we're talking about evidence of some of the earliest life on Earth.

These fossils are almost 2 billion years old.

"Mmhm."

I mean, that's almost half the age of the planet.

"Yeah, sure."

Isn't that wild?

"We get it."

[Music] [Game show music] Live from Vasquez Rocks and Agua Dulce, California.

It's time to play THE RELATIVE DATING GAME!

And now, here's your host, Michelle Barboza-Ramirez.

[Crowd cheering] Thank you!

Thank you, everyone, and welcome to the Relative Dating Game, the only show where contestants can walk away with the ultimate prize.

A thorough understanding of our planet's history.

[Crowd laughing] Let's bring our first contestant.

He's a science teacher from Ohio who says he is in fact, the milk man's son.

Let's welcome Chris Anderson.

[Crowd cheering] So nervous.

I've always wanted to play this game.

Let's begin.

Chris.

Take a look at the rocks behind you.

Which layer of rock is the oldest?

Is it layer A, layer B or layer C?

Well, I know when I make a sandwich, I always start with the bottom layer first.

And I think the earth would do the same thing.

I'm going to go with layer A. That is correct!

Okay Chris, your next question.

Layer B has been found to be 20 million years old.

About how old is layer A?

Is it 15 million years old or 25 million years old?

Well, if layer A is at the bottom, it's got to be the oldest.

So I'm going to go with, 25 million years.

U.S.

Geological Survey says that is correct!

[Applause] Okay, Chris, your last question.

As you can see, the rocks behind us are tilted upwards because we are actually on a fault.

Did the fault form before the rock layers or did it form after?

- Hmhm?

Man, that's really tough.

Well, I know gravity would deposit the sediments horizontally, which means the rocks would have been flat when they were formed.

So that fault would have had to form after the rocks were there.

So I'm going to go with after.

That is absolutely correct!

Yeah!

Apparently faults are not a factor for you.

You answered all three of our questions correctly.

What is Chris's prize?

Chris, you won the latest album by legendary rock conglomerate The Sedimentary Band.

“Wouldn't it be Gneiss” And of course, Michelle's voice on your answering machine.

Thank you so much for playing.

And thank you for being such a wonderful audience.

We'll see you again on THE RELATIVE DATING GAME!

[Music] So my name is Michelle Barboza, and I am a geology professor and a co-host for PBS Eons.

[Woosh, pops] [Ding] So I'm a vertebrate paleontologist specifically, which means that I study ancient life in the forms of fossils.

And that can be ancient bones that can be footprints, that can be leaves.

Anything that tells us about things that used to live on Earth before humans did.

Before we did.

And the vertebrate part of it means that I study animals that have a vertebra.

Right.

So a backbone if you feel along your back.

So there are other paleontologists that specifically study plants or that study snails or other animals that didn't have a backbone.

But I like the bony animals.

I'm going to throw out an animal that a lot of people don't know.

They're called Chalicotheres, and they are the biggest land mammals to have ever existed.

They are super huge, super wonky, really awkward looking guys that lived, oh, maybe like 30 to 40 million years ago.

And they kind of look like derpy giraffe-rhino hybrids.

Look them up.

So my parents are both teachers and they would take me to science and history museums all the time.

And I loved that.

But I hated science.

Like, totally did not like science when I was in school.

I thought it was like equations and chemicals and like really boring stuff.

And then I went to college and I had to take a course.

And so I took a geology course.

And it turns out that, like, science is also getting to go outside and go hiking and like, science is digging for dinosaurs.

And like you, that can be your job.

So once I figured that that was also science, I was on board.

So then I took a paleontology course and that paleontology professor was my mentor.

I went up to him at the start of class and I was like, hi, I think this is cool and maybe I want to study it.

And then, yeah.

Then I started doing my research with him, and, he helped me find internships, and now I teach at the same school with him.

There are different things you can do as a paleontologist, and I think a lot of people know about researching and going on and digging for fossils, which is super fun.

But my favorite part is getting to talk to people about it.

Like I want everyone to know about it.

So I've done stuff like work at museums, which is really fun, and you get to plan different events and how to get people excited about museums.

I've done stuff with a team called Cosplay for Science, where we dress up like Jurassic Park characters and talk about dinosaurs, or we did a Game of Thrones convention.

So we talk about all of this pop culture stuff that people already love, and then we're like, wait, but what about the science behind it that inspired it?

And if you think that, you know, like these Star Wars monsters are cool, like some of those were real and existed here, or like Direwolves were real.

So I just again, like, I just love talking about science and all the cool stuff.

I would say you don't even have to be a scientist to like science.

Like you can be a fan of science and learn about science and that'll matter no matter what profession you go into.

Like if you want to work in politics, we need you to know science.

If you want to be a business person, you need to know science.

So you want to be a teacher, you should know science.

So science is something that's really fun and interesting.

And you don't have to become the ultimate scientist or be the smartest scientist.

Just got to think it's kind of cool and learn about it sometimes.

[Music] So we are here at the museum in Claremont, California, with Gabe Santos, who's the collections manager here, and we're about to take a trip back through time by checking out their fossil collection.

So you ready, Gabe?

Ready!

[Music] So, Gabe, what are we looking at here?

We are looking at trackways that are about 200 million years old from the early Jurassic.

Early Jurassic?

So are these dinosaur fossils?

Yeah, as far as we can tell, a lot of these have that shape that lets us know that they're made by dinosaurs.

Yeah, they do have that like that three, like claw shape.

That's really cool.

So what are some things we can learn about these particular tracks?

We can't really figure out what animals made them, but we can learn a lot about what they were doing while they're alive.

So we got a whole bunch of different kind of species here.

Let's take a look.

What do we got?

We've got some really cool stuff.

So we've got things like brachiopods.

They might look like bivalves, like clams and shells, but they're actually not they're their own group of animal that have their own shell.

Oh, so they're like that, but they're, but they're completely other group.

Yeah.

You can kind of see it.

It does look like like something you might even find on the beach today.

Yeah.

We've also got things like crinoids.

So these are these weird animals.

Some people think they look like plants but they're not.

They have a long stalk on the top of their head.

They've got their, feathery arms that they use to get filter feed out of.

So a lot of cool stuff in there.

Oh, so they're not plants, but they're, they're an animal instead.

They just kind of stick there.

Yeah, they stick out of the ground and just filter feed with their feathery arms.

That's really cool.

So what kind of environment did these guys live in?

So the Kaibab Formation is a limestone formation, which means it was made in some sort of shallow sea, really cool salt water.

Okay.

So this is, this is under, like an ocean, under water.

Then there were all these guys lived?

Yeah.

So this would have been, it wouldn't have been like an ocean, like you and I could, like, jump in today.

This would be, like, a totally alien planet, basically.

Yeah.

It would look very, very different.

Very different animals.

Very different, corals and things like that.

Very cool.

So, Gabe, what are we looking at here?

We are looking at a track slab from the Coconino Sandstone.

Okay.

It's track slab from the Coconino Sandstone.

So, who made these tracks?

Great question.

We actually don't know.

Oh.

So.

- So it's a mystery?

Yeah.

When you have trackways, you don't have any evidence of the actual animal that made it.

Like, feet are kind of the same.

There are a lot of animals.

So you can kind of get a general idea of what made them.

So here we think that's some sort of reptile and some insect, or maybe a giant arachnid might have made these tracks, but because we don't have the actual animal specimen with the tracks, we will probably never really know what made these footprints.

So what can we learn about whoever made the these footprints here?

That's one of my favorite things about paleo ichnology or learning about trace fossils.

You can learn more about an animal's behavior and like movement than you can from the bone.

So from here we can learn about what animals might have lived together right?

We can learn how fast that animal might be moving by measuring its footprints.

And it's gait as it's called.

The, like, distance between its feet.

Okay.

You can even learn a little bit about how they might have interacted with their environment.

So these are, these were made on a sand dune away from like any like water or anything.

And so this was like a almost like a desert.

Yeah.

Okay.

- Yeah.

So these creatures were living in a desert and walking along a sand dune early in the morning and leaving these footprints that got preserved over time.

All right.

So Gabe, what are we looking at here?

What we are looking at is a ripple mark.

These are traces of ancient environment from about 1 billion years ago.

Holy crap.

That's a long time ago.

I can't even think how long ago that is.

Nope.

So this is really neat because there's a there's a lot of like ripple marks here.

How did this form?

Well, basically what happened is a billion years ago, this was the bottom of some sort of river system.

Or maybe like a flood plain, and there was flowing water over here.

And as the water flowed over, it deposited new layers of rock.

And as the water movement kind of deposited them, it kind of made these tiny little sand dunes or ripples.

And those got preserved because those got covered very fast.

And so we have that, ancient trace of the water, and we can even kind of tell the direction that the water was flowing.

So which, which way was it going?

I think based on the way that it was kind of going from here to here, because you can kind of look.

- So from you to me?

Yeah, you can look at where the ripples are and kind of look at the shape.

Yeah.

Yeah.

Okay.

So it does kind of almost look like if you were to go walking to like a creek, it would, you know, almost see something similar to this.

And even even today.

When you do visit Grand Canyon, remember this park is for everybody.

So don't take the fossils.

You can take a selfie or make a drawing.

[Camera shutter noise] Which is cool because you can show your friends or a park ranger who can help you identify it, but leave the fossils here.

Make sure other visitors can discover them for themselves.

And as always, stay on the trails and make sure you take anything you brought on your hike with you back out.

Thanks for watching.

Now, if you'll excuse me, I've got some erosional disconformities to stratify.

We'll see you next time on OutSCider Classroom!

[Music] Major funding is provided by the National Geographic Foundation.

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