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All right, let's get up[br]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[br]pretty psyched about this,

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but the earth is great.

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It's powerful, it's dynamic,[br]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[br]my perspective as a geologist

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in how understanding earth's past

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can help inform and guide[br]decisions that we make today

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about how to sustainably live[br]on earth's surface.

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So there's a lot of exciting things[br]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[br]about one of the things that happens.

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

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

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gets eroded and transported[br]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[br]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[br]mountains in the world,

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and you can see in this satellite photo

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rivers transporting material[br]from those mountains out to the sea.

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You can think of these rivers[br]like bulldozers.

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They're basically taking these mountains[br]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[br]specifically about a river -

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you can see these beautiful patterns[br]that the rivers make

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as they're pushing material[br]down to the sea,

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but these patterns aren't static.

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These rivers are wiggling[br]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[br]is this is the Kosi River.

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So the Kosi River[br]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[br]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[br]about what happened with the Kosi.

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

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So this is a satellite image[br]from August of 2008,

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and this satellite image is colored

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so that vegetations or plants[br]show up as green

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and water shows up as blue.

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So here again you can see[br]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[br]in this region of the world,

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

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and the hazards and inconveniences[br]at minimum that are associated with that.

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But something interesting[br]happened in 2008,

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

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It flooded in a way that's very[br]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[br]are bulldozing sediment,

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they kind of get clogged,

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and these clogs can[br]actually cause the rivers

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to shift their course dramatically.

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So this satellite image[br]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[br]of the field of view here.

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What happened is[br]the Kosi River jumped its banks,

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

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This river moved[br]over 30 miles very abruptly.

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So this river got clogged[br]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[br]these are the previous pathways,

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and you can see this process[br]of river-jumping continues

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as this river moves farther away[br]from its major course.

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So you can imagine[br]in landscapes like this,

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where rivers move around frequently,

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

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But these kinds of processes[br]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[br]that drains most of the continental US.

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It pushes material[br]from the Rocky Mountains

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and from the Great Plains.

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It drains it and moves it[br]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[br]that we're familiar with today,

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but it didn't always flow[br]in this direction.

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If we use the geologic record,

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we can reconstruct[br]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[br]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[br]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[br]as recently as 500 years ago

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that it occupied the pathway[br]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[br]in the Mississippi

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are building land at the interface[br]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[br]densely populated areas on our planet.

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So understanding the dynamics[br]of these landscapes,

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how they formed and how they will[br]continue to change in the future

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is really important[br]for the people that live there.

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So rivers also wiggle.

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

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I want to show you guys[br]some river wiggles here.

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So we're going to fly down[br]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[br]material from the Andean Mountains,

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transporting it across South America

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and dumping it out[br]into the Atlantic Ocean.

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

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

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These rivers wiggle around.

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We can use satellite imagery[br]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[br]any bend or curve in this river,

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

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It changes and evolves[br]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[br]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[br]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[br]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[br]that we live in on earth,

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as this material[br]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[br]to understand these processes

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so we can manage and live[br]sustainably on these landscapes.

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

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is what's going on today[br]at earth's surface.

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

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

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We need more observations[br]to understand these processes more.

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And additionally, we need to know

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how these landscapes are going[br]to respond to changing climate

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and to changing land use

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as we continue to occupy[br]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[br]from the mountains to the sea,

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

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And that stuff that gets stuck[br]in the ground gets buried,

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and through time, we get[br]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[br]go to places like this,

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where we see big, thick stacks[br]of sedimentary rocks,

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and go back in time

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and see what the landscapes[br]looked like in the past.

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We can do this to help reconstruct

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and understand[br]how earth landscapes evolve.

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This is pretty convenient, too,

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

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So this video here[br]is a reconstruction of paleogeography

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for just the first[br]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,[br]sea level has changed,

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we have a lot of different[br]types of landscapes

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and different types of environments[br]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[br]that were deposited at these times.

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

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

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

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and what happened was[br]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[br]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[br]like crocodiles and palm trees

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as far north as Canada[br]and as far south as Patagonia.

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So this was a pretty warm time[br]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[br]that were deposited at this time

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and reconstruct how the landscape changed[br]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[br]laid down 55 million years ago.

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As geologists, we can go[br]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[br]and make measurements and observations,

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and we can measure features.

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For example, the features[br]I just highlighted there

0:09:10.020,0:09:13.476
tell us that this particular river[br]was probably about three feet deep.

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You could wade[br]across this cute little stream

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if you were walking around[br]55 million years ago.

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The reddish stuff that's above[br]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[br]what lived and grew on the landscape

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

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So we can look in detail[br]and reconstruct with some specificity

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how these rivers flowed[br]and what the landscapes looked like.

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So when we do this[br]for this particular place

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at this time,

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if we look what happened[br]before this abrupt warming event,

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

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

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But right at the onset[br]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[br]across the landscape more readily.

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

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to what they would have looked like[br]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[br]and do these kinds of reconstructions

0:10:20.220,0:10:22.836
and understand how[br]earth's landscape has changed

0:10:22.860,0:10:26.636
in response to a climate event like this[br]or a land use event.

0:10:26.660,0:10:28.756
So some of the ways that rivers change

0:10:28.780,0:10:33.556
or the reasons that rivers change[br]their pattern and their movements

0:10:33.580,0:10:37.516
is because of things like with extra water[br]falling on the land's surface

0:10:37.540,0:10:39.476
when climate is hotter,

0:10:39.500,0:10:42.036
we can move more sediment[br]and erode more sediment,

0:10:42.060,0:10:43.900
and that changes how rivers behave.

0:10:44.780,0:10:46.876
So ultimately,

0:10:46.900,0:10:49.516
as long as earth's surface is our home,

0:10:49.540,0:10:52.916
we need to carefully manage[br]the resources and risks

0:10:52.940,0:10:55.916
associated with living[br]in dynamic environments.

0:10:55.940,0:10:59.876
And I think the only way[br]we can really do that sustainably

0:10:59.900,0:11:02.116
is if we include information

0:11:02.140,0:11:06.236
about how landscapes evolved[br]and behaved in earth's past.

0:11:06.260,0:11:07.476
Thank you.

0:11:07.500,0:11:11.940
(Applause)