WEBVTT

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All right, let's get up
our picture of the earth.

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The earth is pretty awesome.

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I'm a geologist, so I get
pretty psyched about this,

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but the earth is great.

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It's powerful, it's dynamic,
it's constantly changing.

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It's a pretty exciting place to live.

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But I want to share with you guys today
my perspective as a geologist

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in how understanding earth's past

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can help inform and guide
decisions that we make today

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about how to sustainably live
on earth's surface.

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So there's a lot of exciting things
that go on on the surface of the earth.

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If we zoom in here a little bit,

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I want to talk to you guys a little bit
about one of the things that happens.

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Material get shuffled around
earth's surface all the time,

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and one of the big thing that happens
is material from high mountains

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gets eroded and transported
and deposited in the sea.

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And this process is ongoing all the time,

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and it has huge effects
on how the landscape works.

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So this example here in south India --

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we have some of the biggest
mountains in the world,

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and you can see in this satellite photo

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rivers transporting material
from those mountains out to the sea.

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You can think of these rivers
like bulldozers.

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They're basically taking these mountains
and pushing them down towards the sea.

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We zoom in a little bit.

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We can see that -

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I'll give you guys an example here.

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So we zoom in a little bit,

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I want to talk to you guys
specifically about a river -

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you can see these beautiful patterns
that the rivers make

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as they're pushing material
down to the sea,

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but these patterns aren't static.

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These rivers are wiggling
and jumping around quite a bit,

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and it can have big impacts on our lives.

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So an example of this
is this is the Kosi River.

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So the Kosi River
has this nice c-shaped pathway,

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and it exits the big mountains of Nepal

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carrying with it a ton of material,

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a lot of sediments that's being
eroded from the high mountains,

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and it spreads out across India

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and moves this material.

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So we're going to zoom in to this area

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and I'm going to tell you a little bit
about what happened with the Kosi.

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It's an example of how dynamic
these systems can be.

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So this is a satellite image
from August of 2008,

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and this satellite image is colored

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so that vegetations or plants
show up as green

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and water shows up as blue.

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So here again you can see
that c-shaped pathway

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that this river takes as it exits Nepal.

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And now this is monsoon season.

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August is monsoon season
in this region of the world,

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and anyone that lives near a river
is no stranger to flooding

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and the hazards and inconveniences
at minimum that are associated with that.

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But something interesting
happened in 2008,

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and this river moved in a way
that's very different.

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It flooded in a way that's very
different than it normally does.

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So the Kosi River is flowing down here,

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but sometimes as these rivers
are bulldozing sediment,

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they kind of get clogged,

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and these clogs can
actually cause the rivers

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to shift their course dramatically.

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So this satellite image
is from just two weeks later.

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Here's the previous pathway,

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that c-shaped pathway,

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and you notice it's not blue anymore.

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But now what we have is this blue pathway

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that cuts down the middle
of the field of view here.

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What happened is
the Kosi River jumped its banks,

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and for reference,
the scale bar here is 40 miles.

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This river moved
over 30 miles very abruptly.

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So this river got clogged
and it jumped its banks.

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Here's an image from about a week later,

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and you can see
these are the previous pathways,

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and you can see this process
of river-jumping continues

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as this river moves farther away
from its major course.

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So you can imagine
in landscapes like this,

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where rivers move around frequently,

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it's really important to understand when,
where and how they're going to jump.

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But these kinds of processes
also happen a lot closer to home as well.

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So in the United States,

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we have the Mississippi River
that drains most of the continental US.

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It pushes material
from the Rocky Mountains

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and from the Great Plains.

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It drains it and moves it
all the way across America

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and dumps it out in the Gulf of Mexico.

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So this is the course of the Mississippi
that we're familiar with today,

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but it didn't always flow
in this direction.

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If we use the geologic record,

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we can reconstruct
where it went in the past.

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So for example, this red area here

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is where we know the Mississippi River
flowed and deposited material

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about 4,600 years ago.

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Then about 3,500 years ago it moved

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to follow the course
outlined here in orange.

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And it kept moving and it keeps moving.

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So here's about 2,000 years ago,

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a thousand years ago,

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700 years ago.

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And it was only
as recently as 500 years ago

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that it occupied the pathway
that we're familiar with today.

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So these processes are really important,

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and especially here, this delta area,

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where these river-jumping events
in the Mississippi

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are building land at the interface
of the land and the sea.

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This is really valuable real estate,

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and deltas like this are some of the most
densely populated areas on our planet.

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So understanding the dynamics
of these landscapes,

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how they formed and how they will
continue to change in the future

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is really important
for the people that live there.

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So rivers also wiggle.

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These are sort of bigger jumps
that we've been talking about.

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I want to show you guys
some river wiggles here.

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So we're going to fly down
to the Amazon River basin,

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and here again we have a big river system

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that is draining and moving and plowing
material from the Andean Mountains,

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transporting it across South America

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and dumping it out
into the Atlantic Ocean.

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So if we zoom in here, you guys
can see these nice, curvy river pathways.

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Again, they're really beautiful,
but again, they're not static.

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These rivers wiggle around.

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We can use satellite imagery
over the last 30 or so years

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to actually monitor how these change.

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So take a minute and just watch
any bend or curve in this river,

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and you'll see it doesn't stay
in the same place for very long.

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It changes and evolves
and warps its pattern.

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If you look in this area in particular,

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I want you guys to notice
there's a sort of a loop in the river

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that gets completely cut off.

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It's almost like a whip cracking

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and snaps off the pathway
of the river at a certain spot.

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So just for reference, again,

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in this location, that river
changed its course over four miles

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over the course of a season or two.

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So the landscapes
that we live in on earth,

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as this material
is being eroded from the mountains

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and transported to the sea,

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are wiggling around all the time.

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They're changing all the time,

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and we need to be able
to understand these processes

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so we can manage and live
sustainably on these landscapes.

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But it's hard to do
if the only information we have

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is what's going on today
at earth's surface.

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Right? We don't have
a lot of observations.

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We only have 30 years' worth
of satellite photos, for example.

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We need more observations
to understand these processes more.

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And additionally, we need to know

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how these landscapes are going
to respond to changing climate

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and to changing land use

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as we continue to occupy
and modify earth's surface.

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So this is where the rocks come in.

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So as rivers flow,

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as they're bulldozing material
from the mountains to the sea,

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sometimes bits of sand and clay
and rock get stuck in the ground.

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And that stuff that gets stuck
in the ground gets buried,

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and through time, we get
big, thick accumulations of sediments

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that eventually turn into rocks.

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What this means is that we can
go to places like this,

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where we see big, thick stacks
of sedimentary rocks,

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and go back in time

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and see what the landscapes
looked like in the past.

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We can do this to help reconstruct

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and understand
how earth landscapes evolve.

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This is pretty convenient, too,

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because the earth has had
sort of an epic history. Right?

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So this video here
is a reconstruction of paleogeography

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for just the first
600 million years of earth's history.

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So just a little bit of time here.

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So as the plates move around,

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we know climate has changed,
sea level has changed,

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we have a lot of different
types of landscapes

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and different types of environments
that we can go back --

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if we have a time machine --

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we can go back and look at,

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and we do indeed have a time machine

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because we can look at the rocks
that were deposited at these times.

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So I'm going to give you
an example of this

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and take you to a special
time in earth's past.

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About 55 million years ago,
there was a really abrupt warming event,

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and what happened was
a whole bunch of carbon dioxide

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was released into earth's atmosphere,

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and it caused a rapid
and pretty extreme global warming event.

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And when I say warm, I mean pretty warm,

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that there were things
like crocodiles and palm trees

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as far north as Canada
and as far south as Patagonia.

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So this was a pretty warm time
and it happened really abruptly.

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So what we can do

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is we can go back and find rocks
that were deposited at this time

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and reconstruct how the landscape changed
in response to this warming event.

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So here, yay, rocks.

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(Laughter)

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Here's a pile of rocks.

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This yellow blob here,

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this is actually a fossil river,

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so just like this cartoon I showed,

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these are deposits that were
laid down 55 million years ago.

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As geologists, we can go
and look at these up close

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and reconstruct the landscape.

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So here's another example.

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The yellow blob here is a fossil river.

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Here's another one above it.

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We can go and look in detail
and make measurements and observations,

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and we can measure features.

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For example, the features
I just highlighted there

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tell us that this particular river
was probably about three feet deep.

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You could wade
across this cute little stream

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if you were walking around
55 million years ago.

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The reddish stuff that's above
and below those channels,

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those are ancient soil deposits.

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So we can look at those to tell us
what lived and grew on the landscape

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and to understand how these rivers
were interacting with their floodplains.

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So we can look in detail
and reconstruct with some specificity

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how these rivers flowed
and what the landscapes looked like.

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So when we do this
for this particular place

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at this time,

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if we look what happened
before this abrupt warming event,

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the rivers kind of carved their way
down from the mountains to the sea,

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and they looked maybe similar to what
I showed you in the Amazon River basin.

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But right at the onset
of this climate change event,

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the rivers change dramatically.

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All of a sudden they got much broader,

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and they started to slide back and forth
across the landscape more readily.

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Eventually, the rivers reverted
back to a state that was more similar

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to what they would have looked like
before this climate event,

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but it took a long, long time.

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So we can go back in earth's time
and do these kinds of reconstructions

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and understand how
earth's landscape has changed

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in response to a climate event like this
or a land use event.

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So some of the ways that rivers change

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or the reasons that rivers change
their pattern and their movements

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is because of things like with extra water
falling on the land's surface

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when climate is hotter,

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we can move more sediment
and erode more sediment,

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and that changes how rivers behave.

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So ultimately,

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as long as earth's surface is our home,

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we need to carefully manage
the resources and risks

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associated with living
in dynamic environments.

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And I think the only way
we can really do that sustainably

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is if we include information

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about how landscapes evolved
and behaved in earth's past.

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Thank you.

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(Applause)