WEBVTT

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Prof: Now today we're
going to be talking about some

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of the major events in the
geological theater.

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This is the second of three
ways that we're looking at the

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history of life.

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The first was rather abstract;
it had to do with major

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transitions and with
reorganization of genetic

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information, units of selection,
things like that.

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That was last time.

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Today we're going to talk about
how life shaped the planet and

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how the planet shaped life.

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So this is a quick run through
a 4.5 billion year process.

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And then next time we're going
to talk about major lessons from

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the fossil record.

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There are a lot of ways of
trying to construct a diagram

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that will give you a feel for
deep time, and it's not so easy.

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I once did a kindergarten class
where I took a bunch of

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kindergartners and I tried to
get them to step off 100 million

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years at a time,
or 10 million years at a time.

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I think I did 10 million years
so that we could take six steps

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and then meet a dinosaur.

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And there are a lot of ways of
doing this,

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but this is not a bad one
because it gives you a diagram

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that shows you about how much of
the existence of the planet has

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been occupied by life;
about how much of it has been a

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story that's mostly of
prokaryotes,

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in other words about half of
the time that life has been on

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the planet,
there have only been

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prokaryotes;
and about how much of it has

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been complicated multicellular
organisms.

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And, of course,
we show up just briefly before

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midnight, on that kind of a
scale.

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So that's one way of looking at
it.

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And learning to think about
deep time is really important if

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you have a taste for
macroevolution,

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and it's certainly important if
you have a taste for geology.

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Now, at the beginning,
we had a reducing atmosphere,

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and the source of O2 was
photosynthetic bacteria.

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I'm just going to check
something here;

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yes, okay.

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So we start off with a reducing
atmosphere,

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and then we have to fill up
essentially,

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once the photosynthetic
bacteria get going--

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and, by the way,
some of them were

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chemosynthetic as well as
photosynthetic--

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once the photosynthetic
bacteria get going and start

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producing a lot of oxygen,
there's a tremendous mass of

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stuff on the face of the earth
that has to be oxygenated before

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there's any free oxygen.

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So that takes quite awhile.

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So until about half of the age
of the planet,

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the concentration of oxygen in
the atmosphere was less than

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0.4%.

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You would all die within a
minute, at that oxygen

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concentration.

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And the evidence that we have
of when there was free oxygen in

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the atmosphere is essentially
the age of the iron mines of the

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world.

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So there was ferrous oxide--it
can dissolve in water--

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floating around in the ocean,
and when the oxygen level of

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the atmosphere got high enough,
it oxidized to ferric oxide,

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and the ferric oxide fell out
of solution,

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and when it fell out of
solution it made the iron mines

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of the world.

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That happened 2.3 billion years
ago.

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This kind of process continued
with other sorts of elements.

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So we have copper coming out at
about 1.7 billion years,

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at a higher concentration of
oxygen.

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And the consequences of free
oxygen are that an ozone layer

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forms in the atmosphere.

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That screens ultraviolet light
and that drops the mutation

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rate,
and it's probably only because

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the mutation rate dropped
significantly with an ozone

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layer that we could evolve large
long-lived organisms.

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Once you have oxygen in the
atmosphere, you can start

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getting nitrates.

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Nitrates are oxygenated
nitrogen.

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So you won't really have
nitrogen fertilizer until you

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have free oxygen,
and that then also became a key

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nutrient for algae.

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So there's a whole sequence of
important chemistry that goes on

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over a period of about 3 billion
years that starts to set up the

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environment that we're familiar
with.

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There are a number of ways of
looking at this.

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This is from Don Desmirais,
at the Ames Research Center.

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He's an astrobiologist and has
specialized in trying to examine

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the question of life on other
planets;

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and they have tried to make
diagrams like this for other

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planets as well.

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So in our early environment,
the sun was only about 70% as

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hot as it is now,
and by about 500 million year

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ago it was up to 95%.

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The early environment of the
earth was a meteorite

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bombardment.

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So if you were out looking at
the night sky--

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which, of course,
you wouldn't have been able to

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do because the meteorite
bombardment was so intense that

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you would've been standing on a
boiling lake of lava--

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but, if you were out,
looking at the night sky,

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on your boiling lake in lava,
in your terminator suit or

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whatever,
you would've seen lots and lots

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of big meteorites coming in
every night;

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and that gradually tailed off.

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Okay?

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The heat flow out of the molten
mass forming the core of the

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earth has tended to drop off and
stabilize.

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So it has a continuous
radioactive input,

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but the original heat from the
entire planet being molten has

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gradually radiated.

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So we're stabilizing at about
the heat flow from the

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radioactivity in the earth.

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And the continents formed and
stabilized at about 1.8 to 2

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billion years ago,
and these things called major

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orogenies are major chunks of
continent coming up and major

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mountain ranges getting built.

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Now the collision of plate
tectonics has continued to form

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mountain ranges since then,
but this just stabilizing the

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continental crust took about 2
billion years.

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If you look at the history of
the atmosphere,

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of course we're currently
worried about the costs:

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carbon taxes,
and global warming,

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and anthropogenic effects on
the CO2 concentration in the

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atmosphere.

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But at the origin,
the CO2 level was much,

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much higher.

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The atmosphere was more than
what we would call 100% CO2,

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because it was thicker at that
point, and it blew off.

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This has dropped down here to
about 3 times 10^(-4)

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atmospheric pressure for CO2.

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It's actually a small component.

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Oxygen rose and probably
reached present levels at about

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5 or 600 million years ago.

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It's interesting that if it
went up a little bit more,

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a room like this could catch on
fire, just spontaneously.

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At about 27%,
wood will catch on fire

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spontaneously,
at current atmosphere

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pressures.

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So this is another way of
looking at that process.

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At the beginning,
we had water,

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hydrogen, carbon monoxide,
lots of steam;

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a lot of that escaped to space.

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There were meteorite impacts.

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The CO2 curve has gone down.

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The oxygen curve has done up;
there's some indications it's

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gone up stepwise.

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Temperature,
we don't really know accurately

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what the temperature was back
before 3.5 billion years,

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but we can be pretty sure that
at and after the origin of life,

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water was liquid on the surface
of the planet;

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so that sets an upper limit of
100 degrees Centigrade.

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And temperature has gone up and
down in a number of cycles over

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a fairly long period,
and there have been some major

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Ice Ages.

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How do you recover that?

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Well one of the ways that you
can do it is you can look,

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if you have leaves of fossil
plants--

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so if you've already got plants
that evolved and they have

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leaves;
so maybe about the last 300

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million years or so--you can
look at the stomatal ratios on

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them.

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So this has been calibrated.

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Plants have to make more holes
in their leaves;

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if there's less carbon,
they have to have a bigger

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mouth so that they can feed more
efficiently.

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And they can have fewer holes
in their leaves if--and they can

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be smaller--if there's more
carbon in the atmosphere.

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And so basically this allows
you to plot and estimate a

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curve.

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And it looks like there was
massive withdrawal of carbon

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dioxide from the atmosphere from
the Ordovician,

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through the Permian,
right here.

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And then there was a
re-injection here,

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going into the Triassic--and
when we come to the Permian Mass

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Extinction,
I want you to remember this dip

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here,
and this re-injection--and then

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there's been a more gradual
withdrawal down to the current

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level.

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So the earth was much more of a
greenhouse in the past than it

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is today.

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And if we look at where the
carbon dioxide went,

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a lot of it got locked up in
limestone, in sedimentary rock.

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Then a lot of it is in organic
carbon.

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A lot of it is in the ocean,
is bicarbonate.

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These are by far the largest
sinks, but there's a lot of

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bicarbonate ion in the ocean.

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This is all the fossil fuel on
the planet right here;

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so this is all the coal and oil.

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And you can see that of the
original amount of carbon that

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was in the earth's atmosphere,
that's a pretty small fraction;

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it's a bit less than
1/1000^(th) of 1%.

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And in living biomass,
there's a very,

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very small part.

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So basically if you look at
that, you can see that the

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carbon balance of the planet is
extremely dependent upon what

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happens in rocks,
and that if there are small

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geological changes in the cycle
of how carbon is going in and

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out of rock,
and whether it's being

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subducted as plate tectonics
proceeds or not,

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is going to make a much bigger
difference to the amount of

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carbon in the atmosphere than
the amount of fossil fuel that's

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being burned,
or the tree cover of the planet

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in forests,
which would be the living

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biomass term down here.

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However, this is a slow
process, and this is a fast

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process.

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So on the scale of human
lifespans, this is in fact more

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important.

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But on the scale of say
somewhere out at around 100,000,

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out into the millions of years,
what's happening in sedimentary

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rock is really critical.

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Now if we look at the way that
life structures the planet,

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one of the very important
things that life has done is

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that it's made soil.

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And we don't really start to
get soil,

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which is a big complicated
piece, an engineered niche that

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plants create,
until we get complicated plants

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on land.

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So the first ones on land are
probably things like liverworts,

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and our first fossils are club
mosses,

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and that's happening back at
around 400 to 500 million years

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ago.

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There are fossil soils,
and those fossil soils have

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roots in them,
and those roots suggest that

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the first time that there were
real trees was at about 350 to

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400 million years ago.

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Remember back to that clock.

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This is relatively recent,
in terms of the age of the

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planet.

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So we get really modern soils
with layering,

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and with evidence of seed
plants in the Carboniferous.

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So that is the age at which
most of the coal mines of the

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earth were laid down;
it's about 300 million years

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ago.

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If you take Interstate 80,
west of New York,

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and you go out to where it
crosses from New Jersey into

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Pennsylvania,
at the Delaware Water Gap,

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there's a cut there that you
can look up at,

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and what you're looking at is
the outwash of rivers that were

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coming down off of the Taconic
mountain range.

13:54.759 --> 14:02.849
And if you look into that cut,
it's remarkably clean.

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It's a preservation of what was
coming down rivers 500 million

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years ago, and it's an
indication that there was very

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little soil.

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It is basically at or before
this process occurs.

14:19.038 --> 14:23.198
And that mountain range was
formed when Pangaea formed,

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which is at around 550 to 600
million years ago,

14:28.740 --> 14:32.080
and caused the Taconic orogeny,
and that put up a mountain

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range on the border between
Connecticut and New York that

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was about as high as the
Himalayas,

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but it didn't have any forests
on it,

14:39.850 --> 14:43.100
and it had a very high erosion
rate because there weren't

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plants to stabilize the soil.

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And we can see,
in the Delaware Water Gap,

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what washed off that mountain
range.

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It's all worn down now,
and if we come back in another

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500 million years,
the Himalayas will all be worn

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down.

14:57.379 --> 15:01.069
But, with the Himalayas,
there will be a bit more soil

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in the outwash.

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The guys that have really in
the past engineered the planet,

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and that continue to do so,
are the bacteria;

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and by that I mean both the
archaea and the eubacteria.

15:19.509 --> 15:25.589
They are the ones that play a
huge role in the carbon cycle.

15:25.590 --> 15:27.710
They're producing and
oxygenating methane.

15:27.710 --> 15:29.600
They're fixing carbon dioxide.

15:29.600 --> 15:32.730
In the nitrogen cycle,
the bacteria are fixing

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nitrogen from the atmosphere;
they fix it as ammonia.

15:36.288 --> 15:37.968
They oxygenate ammonia to
nitrate;

15:37.970 --> 15:40.090
they de-nitrify nitrates to
ammonia.

15:40.090 --> 15:43.230
And this is a kind of
biochemistry that just about

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nobody else has.

15:44.389 --> 15:48.789
So these are essential things;
the nitrogen in all of the

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proteins on the planet is
essentially originating through

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bacterial processes.

15:54.080 --> 15:56.630
So that's how it's getting from
the abiotic world into the

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living world.

15:57.299 --> 16:01.279


16:01.278 --> 16:06.758
There are sulfur bacteria that
are arguably extremely ancient,

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and which evolved in an
environment in which much of the

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energy coming into living
systems was coming from things

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like sulfur,
rather than from sunlight,

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and they oxidize hydrogen
sulfide to sulfate;

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they reduce sulfate to hydrogen
sulfide.

16:20.820 --> 16:24.430
And iron bacteria are
converting ferrous to ferric

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iron, and they're influencing a
degradation of manganese and

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copper deposits.

16:30.240 --> 16:34.270
A lot of this is now going on
at spreading centers at

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mid-ocean ridges,
or it is going on where there

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is heat flow which is taking
ocean water through the ocean

16:41.696 --> 16:44.116
crust,
and there are bacteria that are

16:44.124 --> 16:47.224
sitting just below the ocean
crust that are sitting in a

16:47.217 --> 16:50.817
stream of basically hot chemical
soup that's coming through,

16:50.820 --> 16:54.330
and when they do these
reactions, often they leave a

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metal deposit behind;
which is why the floor of the

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Pacific Ocean is covered with
manganese nodules that people

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are thinking about mining at a
depth of about five kilometers.

17:04.920 --> 17:09.890
If you go down into the earth's
crust, it turns out that the

17:09.890 --> 17:14.440
biosphere extends below our feet
several kilometers;

17:14.440 --> 17:17.270
bacteria are active that far
down into the soil,

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and they are carrying out
things like this.

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So they are really key players
in structuring the environment

17:25.318 --> 17:29.088
in which we live,
and they do a lot of services

17:29.090 --> 17:33.350
that we simply take for granted
and frankly hadn't even noticed

17:33.347 --> 17:36.367
until about the last hundred
years of so.

17:36.368 --> 17:41.988
Okay, so those are all aspects
of how life has modified the

17:41.988 --> 17:42.858
planet.

17:42.858 --> 17:46.588
How has the planet modified
life?

17:46.588 --> 17:50.718
Well there are at least three
or four big chapters here.

17:50.720 --> 17:52.070
One is through continental
drift;

17:52.069 --> 17:54.469
another is glaciation;
mass extinction;

17:54.470 --> 17:55.840
and then local catastrophes.

17:55.838 --> 17:59.748
And continental drift and mass
extinctions are both out there

17:59.750 --> 18:02.880
at the scale of hundreds of
millions of years.

18:02.880 --> 18:07.010
Glaciation has two scales.

18:07.009 --> 18:09.799
There are times in the planet's
history when it's been

18:09.800 --> 18:12.550
relatively cold;
basically there've been at

18:12.553 --> 18:16.163
least three times when it's been
really quite cold.

18:16.160 --> 18:18.560
But within those longer periods
that are cold,

18:18.555 --> 18:20.945
the glaciers have come and gone
many times.

18:20.950 --> 18:24.150
So the North American
glaciation lasted 2.5 million

18:24.153 --> 18:27.483
years, and the glaciers came and
went about 15 times,

18:27.483 --> 18:28.833
in North America.

18:28.828 --> 18:33.568
The local catastrophes,
it all depends on which

18:33.569 --> 18:36.249
particular kind that is.

18:36.250 --> 18:38.470
You'll see that they occur at
different time scales.

18:38.470 --> 18:43.240
The point of all of this is
that often the past

18:43.237 --> 18:48.677
configuration of the planet,
whether it's the location of

18:48.676 --> 18:52.476
the continents,
or the temperature of the

18:52.481 --> 18:57.681
earth, or whether you could
expect to live in a secure

18:57.680 --> 19:01.430
environment,
have at times been extremely

19:01.430 --> 19:04.390
different from what we currently
see.

19:04.390 --> 19:07.200
And so it is not only
important, if you want to

19:07.201 --> 19:10.491
understand evolution,
to cultivate a sense of deep

19:10.487 --> 19:14.247
time, it's also important to
cultivate a sense of different

19:14.250 --> 19:16.490
time;
sometimes deep time was really

19:16.491 --> 19:19.191
different, and that's what I'm
trying to get at,

19:19.190 --> 19:20.970
by showing you these things.

19:20.970 --> 19:25.560
So here's the last 400 million
years of continental drift.

19:25.558 --> 19:28.348
And, by the way,
people are producing models

19:28.352 --> 19:32.122
that can now take this back to
about oh a billion years.

19:32.118 --> 19:34.518
Of course, the further you go
back,

19:34.519 --> 19:36.269
the harder it is to reconstruct
it,

19:36.269 --> 19:38.949
because the continents have
come together and come apart,

19:38.950 --> 19:41.950
and come together and come
apart, in a long-term cycle

19:41.948 --> 19:44.668
several times,
and in so doing they kind of

19:44.673 --> 19:47.073
wipe out the traces of their
history.

19:47.068 --> 19:50.298
So it's really quite a feat to
try to reconstruct it.

19:50.298 --> 19:52.538
And I'd just like to point out
a couple of things here.

19:52.539 --> 19:53.989
This is Gondwana.

19:53.990 --> 19:56.790
So Pangaea was a little bit
earlier than this;

19:56.788 --> 19:59.238
that was when all of the
continents were together.

19:59.240 --> 20:03.450
South America and Africa and
Antarctica and Australia stuck

20:03.450 --> 20:06.790
together--and India--stuck
together for awhile,

20:06.788 --> 20:08.748
before they came apart.

20:08.750 --> 20:12.680
There is an interesting thing
going on right here.

20:12.680 --> 20:13.610
Here's New Haven.

20:13.608 --> 20:16.288
If you go out to Lighthouse
Park in New Haven,

20:16.288 --> 20:19.748
you'll see some rocks there,
and if you trace where the

20:19.753 --> 20:22.323
closest relatives of those rocks
are,

20:22.318 --> 20:26.108
on the other side of the ocean,
they're in Rabat,

20:26.109 --> 20:26.899
Morocco.

20:26.900 --> 20:28.650
Okay?

20:28.650 --> 20:31.040
So you can actually see the
same kind of rock on the other

20:31.040 --> 20:31.880
side of the ocean.

20:31.880 --> 20:35.330
And that's when that happened;
that's 250 million years old.

20:35.328 --> 20:37.668
Anybody know how old East Rock
is?

20:37.670 --> 20:40.990


20:40.990 --> 20:43.460
East Rock's 225 million years
old.

20:43.460 --> 20:46.030
When the Atlantic opened--you
see the Atlantic opening

20:46.032 --> 20:48.412
here--there were a series of
rifts that opened up,

20:48.413 --> 20:50.213
one of which became the
Atlantic;

20:50.210 --> 20:54.380
another one became the
Connecticut River Valley.

20:54.380 --> 20:56.590
It didn't open,
but it went part way,

20:56.588 --> 20:59.408
and then it had a valley
filling lava flow that filled it

20:59.407 --> 21:02.097
up,
and then the flow tipped,

21:02.099 --> 21:07.169
and it tipped pointing west,
and it cracked in a number of

21:07.174 --> 21:09.134
places,
and that's what's East Rock,

21:09.125 --> 21:10.985
West Rock,
and all the other such

21:10.987 --> 21:14.157
formations that go up through
central Massachusetts to

21:14.162 --> 21:15.362
southern Vermont.

21:15.359 --> 21:19.639
That was a big lava flow;
filled up a big rift valley.

21:19.640 --> 21:23.700
So that happened right here.

21:23.700 --> 21:30.800
Now when Gondwana split up,
it had some things living on

21:30.795 --> 21:31.435
it.

21:31.440 --> 21:35.060
The ratite birds,
and they are flightless and

21:35.055 --> 21:38.915
they don't swim,
and essentially they got rafted

21:38.916 --> 21:41.296
around on pieces of rock.

21:41.298 --> 21:44.728
And it's interesting,
if you think about when

21:44.730 --> 21:48.330
Gondwana split up,
it indicates that the ancestor

21:48.328 --> 21:52.438
of these birds was already alive
and living across that range of

21:52.444 --> 21:55.484
geography,
at that point.

21:55.480 --> 22:00.240
And you can lay a molecular
phylogeny of the ratites onto

22:00.243 --> 22:05.013
these continents and it just
ties them right together.

22:05.009 --> 22:06.579
Okay?

22:06.578 --> 22:11.458
There's another thing that
happened with the breakup of

22:11.455 --> 22:12.355
Pangaea.

22:12.358 --> 22:14.968
Laurasia went north,
Gondwana went south.

22:14.970 --> 22:18.910
In between, for awhile,
there was a thing called the

22:18.905 --> 22:19.905
Tethys Sea.

22:19.910 --> 22:22.790
And this is the configuration
of the continents about 50

22:22.794 --> 22:24.634
million years ago,
in the Eocene.

22:24.630 --> 22:26.170
By the way, the Eocene was
quite warm;

22:26.170 --> 22:28.930
it was really a very tropical
period.

22:28.930 --> 22:32.800
And at that time there was
either--

22:32.798 --> 22:37.298
there was a warm kind of
Mediterranean coastline that

22:37.304 --> 22:40.774
stretched from eastern North
America,

22:40.769 --> 22:43.149
through Nepal,
what is now Nepal,

22:43.146 --> 22:45.596
into what is now eastern China.

22:45.598 --> 22:50.108
This was before India rafted
north and Africa came north and

22:50.113 --> 22:51.953
closed off South Asia.

22:51.950 --> 22:56.650
And this is what is thought to
have accounted for some of the

22:56.654 --> 23:01.204
similarities in the plants that
you find in the Appalachian

23:01.201 --> 23:03.321
Mountains and in China.

23:03.318 --> 23:05.498
And there are many affinities
here.

23:05.500 --> 23:10.490
The rhododendrons, viburnum;
there are a number of tree

23:10.491 --> 23:15.641
species that share a
phylogenetic relationship across

23:15.636 --> 23:21.076
that huge geographical distance,
and it's thought to have been

23:21.078 --> 23:24.838
the signature of a corridor
along which seeds could move 50

23:24.837 --> 23:26.197
million years ago.

23:26.200 --> 23:29.280


23:29.279 --> 23:31.169
Now how about glaciers?

23:31.170 --> 23:35.730
Well here is a fairly deep
timescale.

23:35.730 --> 23:38.730
So this is the Phanerozoic;
the Phanerozoic is the term for

23:38.731 --> 23:41.631
everything that's happened since
the Cambrian started.

23:41.630 --> 23:44.060
So this is the Phanerozoic here.

23:44.058 --> 23:46.198
So this is at about 500 million
years.

23:46.200 --> 23:50.120
This is about 600 million
years, and there's evidence for

23:50.118 --> 23:53.478
one which is deeper,
at about a billion years.

23:53.480 --> 23:55.740
So this is an Ice Age,
this is an Ice Age.

23:55.740 --> 23:58.330
It looks there was an
Ordovician Ice Age,

23:58.328 --> 24:00.978
it looks like there was a
Permian Ice Age,

24:00.983 --> 24:04.743
and then there was an Ice Age
just in the Pleistocene.

24:04.740 --> 24:09.950
So about five Ice Ages.

24:09.950 --> 24:12.940
Interestingly,
this one, which came before the

24:12.936 --> 24:16.586
Cambrian, may have been a time
when the earth was almost

24:16.587 --> 24:18.577
entirely covered with ice.

24:18.578 --> 24:22.678
There are signatures you can
find in the rocks of what

24:22.684 --> 24:25.304
latitude you're at,
whether you're close to the

24:25.304 --> 24:27.824
equator or not,
and there are other signatures

24:27.817 --> 24:31.497
you can find in the rocks that
give you how cold it was.

24:31.500 --> 24:34.950
These are usually in the form
of isotope ratios for things

24:34.952 --> 24:37.682
like oxygen and carbon and stuff
like that.

24:37.680 --> 24:41.680
And at this point the entire
earth may have been a snowball,

24:41.680 --> 24:44.380
and only the things that were
very,

24:44.380 --> 24:48.560
very close to the equator may
have come through,

24:48.558 --> 24:51.368
because if it really was a
snowball,

24:51.368 --> 24:56.448
then there was ice covering the
world's oceans.

24:56.450 --> 25:00.060
That is an interesting issue,
and it's one that will probably

25:00.057 --> 25:03.307
cause people to speculate and
publish for quite awhile,

25:03.305 --> 25:05.465
because it's so hard to
resolve;

25:05.470 --> 25:08.260
there's not too much data,
it's a long time ago.

25:08.259 --> 25:12.689
The Permian glaciation,
however, is much better

25:12.686 --> 25:13.646
studied.

25:13.650 --> 25:18.100
Remember that in the Permian,
Gondwana is still together.

25:18.098 --> 25:21.588
It breaks up at about 225
million years ago;

25:21.589 --> 25:24.339
somewhere between 225 and 250.

25:24.339 --> 25:31.009
Well the Permian is at 250;
about 251 I think.

25:31.009 --> 25:35.309
And there was a southern ice
cap that was on- actually

25:35.305 --> 25:40.245
connected, and actually these
continents were all together;

25:40.250 --> 25:43.100
and you can see from the arrows
the direction in which the ice

25:43.096 --> 25:43.746
was flowing.

25:43.750 --> 25:47.870
And I think it's really cool
that you can find rocks,

25:47.865 --> 25:51.025
from Africa,
that were scraped off by the

25:51.030 --> 25:53.960
glaciers and deposited in
Brazil.

25:53.960 --> 25:57.360
Before plate tectonics came
along, nobody had any idea how

25:57.358 --> 25:58.968
that could have happened.

25:58.970 --> 26:01.640
And if you stand on the top of
Table Mountain,

26:01.640 --> 26:04.490
in Cape Town today--which is
something I recommend that any

26:04.489 --> 26:07.289
of you that have the opportunity
to go to Cape Town do;

26:07.288 --> 26:10.128
it's really a very beautiful
place--you can still see the

26:10.125 --> 26:13.055
grooves in the rock from where
the glaciers moved over Cape

26:13.064 --> 26:16.214
Town;
they're 250 million years old.

26:16.210 --> 26:20.190


26:20.190 --> 26:25.080
The climate since then has
actually mostly been warm.

26:25.078 --> 26:29.468
So this, if you look on this
set of maps--this is 50 million

26:29.467 --> 26:31.927
years ago;
35 million years ago;

26:31.930 --> 26:35.160
15 million years ago;
middle of the Pleistocene,

26:35.163 --> 26:39.323
about 1.5 million years ago;
and very close to today,

26:39.321 --> 26:43.841
mid-Holocene would be say about
5000 years ago--

26:43.838 --> 26:47.368
and you look at how much of the
planet is temperate and

26:47.374 --> 26:51.684
tropical,
look at how tropical the Eocene

26:51.681 --> 26:52.251
was.

26:52.250 --> 26:55.480
That was all tropical
rainforest, and the Oligocene

26:55.480 --> 26:58.650
was still- there was still a
huge area of tropics,

26:58.647 --> 27:01.877
and the Miocene still had
pretty good tropics.

27:01.880 --> 27:05.180
But at the last glacial
maximums, the tropical

27:05.181 --> 27:08.411
rainforests were reduced to a
few patches.

27:08.410 --> 27:11.970


27:11.970 --> 27:15.060
We're living today in a
relatively cold,

27:15.064 --> 27:16.894
relatively dry world.

27:16.890 --> 27:18.490
That's what we think is normal.

27:18.490 --> 27:22.240


27:22.240 --> 27:27.880
If we were to come in a polar
orbiting satellite and look down

27:27.884 --> 27:31.404
at the planet say 20,000 years
ago,

27:31.400 --> 27:35.360
30,000 years ago,
we would've seen that where

27:35.363 --> 27:40.593
we're sitting right here is
under probably about a mile and

27:40.587 --> 27:42.207
a half of ice.

27:42.210 --> 27:46.080
The leading edge of it is
pushing stuff off of the

27:46.084 --> 27:50.354
continent that becomes Long
Island and Block Island and

27:50.353 --> 27:54.753
Martha's Vineyard and Nantucket;
that's the terminal moraine of

27:54.747 --> 27:55.467
this glacier.

27:55.470 --> 27:59.710


27:59.710 --> 28:05.380
Scandinavia and Northern
England are completely under

28:05.383 --> 28:08.333
ice, as is the North Sea.

28:08.329 --> 28:10.459
The Sahara Desert was humid.

28:10.460 --> 28:12.790
You can go into the middle of
the Sahara Desert and you can

28:12.785 --> 28:14.585
see rock paintings that humans
made there,

28:14.588 --> 28:17.798
where they're recording
hippopotamuses and things like

28:17.804 --> 28:19.304
that,
living in the middle of the

28:19.301 --> 28:24.021
Sahara,
at this time.

28:24.019 --> 28:28.019
And we'll see in a minute that
the major tropical forests

28:28.017 --> 28:28.657
shrank.

28:28.660 --> 28:32.020
So this is more or less the
global pattern.

28:32.019 --> 28:34.439
The grey now is ice.

28:34.440 --> 28:37.320
The green is tropical forest.

28:37.318 --> 28:46.218
The red and orange are--excuse
me, the green is grassland;

28:46.220 --> 28:50.800
the orange is rainforest.

28:50.798 --> 28:55.088
So there are tropical forest
refugia, in certain places.

28:55.088 --> 29:00.398
And if you were to go into the
south,

29:00.400 --> 29:03.950
what is now the South China
Sea, which is currently covered

29:03.945 --> 29:06.925
by water,
elephants and tigers could walk

29:06.932 --> 29:09.542
out,
over that, because it was dry

29:09.536 --> 29:11.256
land--
enough water had been tied up

29:11.263 --> 29:13.343
in the ice to drop the sea level
down that much--

29:13.338 --> 29:15.898
and that is how they got to
Borneo.

29:15.900 --> 29:22.580
So they could actually just
move down from Asia and get out

29:22.577 --> 29:26.647
as far as Borneo,
but they couldn't make it

29:26.650 --> 29:29.830
across Wallace's Line--
there is a deep-water passage

29:29.826 --> 29:32.976
there that Alfred Russel Wallace
documented in the biogeography

29:32.983 --> 29:35.543
of Indonesia--
and they couldn't make it to

29:35.539 --> 29:37.049
Australia or New Guinea.

29:37.048 --> 29:40.968
So the sea level has gone up
and down, and that's changed

29:40.973 --> 29:45.113
continental margins and the
ability of things to move around

29:45.108 --> 29:45.948
in them.

29:45.950 --> 29:48.570
So that's impact of glaciations.

29:48.569 --> 29:52.019
What about mass extinctions?

29:52.019 --> 29:57.339
There've been two biggies,
end-Permian and end-Cretaceous.

29:57.338 --> 30:04.048
And at the end of the Permian
not only did the trilobites

30:04.050 --> 30:07.640
disappear,
but in fact the estimate is

30:07.644 --> 30:11.714
that 97% of all marine
invertebrate species disappeared

30:11.713 --> 30:13.903
at the end of the Permian.

30:13.900 --> 30:18.310
That is an extremely close
brush with sterilizing the

30:18.307 --> 30:22.057
planet;
it came pretty close.

30:22.058 --> 30:26.058
At the end of the Cretaceous
the things that disappeared,

30:26.058 --> 30:30.498
that we probably would like to
have around to look at,

30:30.500 --> 30:32.260
if we possibly
could--ammonites,

30:32.260 --> 30:35.090
dinosaurs--
almost everything that lived on

30:35.087 --> 30:37.257
land,
that was bigger than five

30:37.261 --> 30:40.161
kilos, went extinct,
and about 70% of the marine

30:40.156 --> 30:41.966
invertebrate species went
extinct.

30:41.970 --> 30:44.470
So this was a big one,
but the biggest was the Permian

30:44.474 --> 30:45.094
extinction.

30:45.089 --> 30:47.749
So these are the trilobites.

30:47.750 --> 30:52.530
They had been around since the
late-Cambrian--

30:52.529 --> 30:55.379
mid-Cambrian to
late-Cambrian--so they had been

30:55.383 --> 30:57.743
around for about 250 million
years,

30:57.740 --> 31:02.010
and they went extinct at the
end of the Permian.

31:02.009 --> 31:04.459
And these are ammonites.

31:04.460 --> 31:09.830
In fact, the chambered nautilus
is fairly close to being an

31:09.830 --> 31:12.620
ammonite;
it would be sort of a modern

31:12.617 --> 31:14.257
survivor of this lineage.

31:14.259 --> 31:18.129
So they were squid-like
creatures that had curved

31:18.133 --> 31:18.863
shells.

31:18.858 --> 31:24.238
And if we look at the diversity
curve for--so this is the number

31:24.243 --> 31:28.803
of families that you could find;
these are mostly marine

31:28.798 --> 31:30.448
invertebrate families.

31:30.450 --> 31:31.320
Okay?

31:31.318 --> 31:32.838
So the number of families of
organisms.

31:32.838 --> 31:36.818
This scale goes from 0 up to
about 1000.

31:36.818 --> 31:39.768
This is the beginning of the
Cambrian, right here.

31:39.769 --> 31:42.969
This is the Vendian,
and then the Cambrian begins

31:42.971 --> 31:43.441
here.

31:43.440 --> 31:46.050
This is the Ordovician,
the Silurian,

31:46.048 --> 31:49.088
Devonian, Carboniferous,
Permian, Triassic,

31:49.093 --> 31:51.633
Jurassic, Cretaceous,
Tertiary.

31:51.630 --> 31:54.930
So this is the Age of Dinosaurs
here;

31:54.930 --> 31:56.630
this is the Age of Mammals here.

31:56.630 --> 32:00.420
And you can see that most of
the last 550 million years of

32:00.416 --> 32:03.536
history is a history of marine
invertebrates.

32:03.538 --> 32:06.628
This is a mass extinction at
the Ordovician.

32:06.630 --> 32:08.770
This is a mass extinction at
the Devonian.

32:08.769 --> 32:11.769
This is the Permian mass
extinction, and this is the

32:11.771 --> 32:13.481
Cretaceous mass extinction.

32:13.480 --> 32:21.710
The red is the modern fauna,
the green is the Cambrian

32:21.713 --> 32:30.723
creatures, and the blue is the
stuff that originated in the

32:30.723 --> 32:32.903
Paleozoic.

32:32.900 --> 32:35.970
So you can see that we still
have--almost all the Cambrian

32:35.970 --> 32:36.940
things are gone.

32:36.940 --> 32:40.880
We still have families of
things that originated in the

32:40.881 --> 32:43.961
Paleozoic,
and what we think of as the

32:43.959 --> 32:48.369
modern creatures really started,
some of them started way back

32:48.373 --> 32:51.403
in the Cambrian,
but they built up a lot in the

32:51.404 --> 32:56.554
Carboniferous and Permian,
and then radiated again in the

32:56.551 --> 32:57.661
Triassic.

32:57.660 --> 33:02.860
So what caused that big
extinction?

33:02.858 --> 33:10.508
Well Gondwana was breaking up,
and so--Laurasia was also

33:10.509 --> 33:18.159
separating from Gondwana--so
Pangaea was breaking up.

33:18.160 --> 33:21.830
At that time there was
large-scale volcanism,

33:21.832 --> 33:26.842
and at that time there was a
lack of oxygen in the oceans.

33:26.838 --> 33:29.858
If you go to the Black Sea
today--the Black Sea is sort of

33:29.864 --> 33:32.204
the model for what this ocean
looked like.

33:32.200 --> 33:36.760
The top oh twenty meters or so
of the Black Sea is oxygenated

33:36.761 --> 33:38.361
and has fish in it.

33:38.358 --> 33:42.468
The Black Sea at its deepest
point is about two miles deep,

33:42.470 --> 33:47.120
and everything from twenty
meters, down to the bottom of

33:47.119 --> 33:50.559
the ocean,
is anoxic, and it stinks like

33:50.559 --> 33:51.609
rotten eggs.

33:51.609 --> 33:53.279
Okay?

33:53.279 --> 33:57.209
Imagine the entire world's
ocean being in that state:

33:57.213 --> 34:00.623
a very thin,
oxygenated, clear upper layer;

34:00.618 --> 34:03.638
and everything below it
basically anoxic:

34:03.642 --> 34:07.852
no vertebrates can live in it;
it's dominated by bacteria;

34:07.849 --> 34:09.069
and it stinks like rotten eggs.

34:09.070 --> 34:15.350


34:15.349 --> 34:19.169
Some people have suggested that
there were extraterrestrial

34:19.172 --> 34:20.822
influences at the time.

34:20.820 --> 34:26.800
It's been difficult to find a
meteorite crater of exactly the

34:26.795 --> 34:27.985
right age.

34:27.989 --> 34:32.129
It doesn't mean there aren't
any--absence of evidence is not

34:32.134 --> 34:34.934
evidence of absence--
but plate tectonics has

34:34.931 --> 34:38.071
remodeled the surface of the
planet extensively since then,

34:38.070 --> 34:40.820
and it's quite possible that
there was a big meteorite crater

34:40.824 --> 34:42.894
but it got subducted and it's
been erased,

34:42.889 --> 34:44.509
so that we can't see it.

34:44.510 --> 34:47.870
At any rate,
this is a fertile area for

34:47.871 --> 34:50.111
speculation,
and people have thought of

34:50.110 --> 34:52.990
asteroids,
comets and supernovas that

34:52.992 --> 34:58.492
might have affected the planet
at the end of the Permian.

34:58.489 --> 35:02.699
It seems likely that it's the
breakup of the continents and

35:02.702 --> 35:06.152
large-scale volcanism,
but I can't really claim that

35:06.150 --> 35:08.570
we really know what caused the
extinction.

35:08.570 --> 35:12.590
If you go to Siberia,
you can find what are called

35:12.588 --> 35:14.308
the Siberian traps.

35:14.309 --> 35:17.499
These are among the largest
flood basalt lava flows on the

35:17.496 --> 35:19.896
planet, and they have just the
right age;

35:19.900 --> 35:22.620
they're at about 251 million
years.

35:22.619 --> 35:30.579
And we know that the extinction
lasted not too long;

35:30.579 --> 35:32.069
it was a few 10,000 years.

35:32.070 --> 35:34.200
It happened both on land and in
the oceans,

35:34.199 --> 35:39.199
and the organisms that went out
in the oceans were the ones that

35:39.204 --> 35:44.054
were particularly susceptible to
changes in the gas regime.

35:44.050 --> 35:46.230
So that would suggest very high
CO2 levels.

35:46.230 --> 35:49.500


35:49.500 --> 35:53.140
So one idea is this:
there were massive volcanic

35:53.139 --> 35:54.919
outbreaks in Siberia.

35:54.920 --> 35:56.550
That caused global warming.

35:56.550 --> 36:00.800
That global warming then
triggered the release of a huge

36:00.795 --> 36:04.575
amount of methane that was
stored in the ocean.

36:04.579 --> 36:05.459
Okay?

36:05.460 --> 36:07.790
This is this Black Sea-like
world ocean.

36:07.789 --> 36:11.389
The methane then gets oxidized
to carbon dioxide,

36:11.387 --> 36:15.137
and essentially extinctions
happen by poisoning and

36:15.135 --> 36:16.405
asphyxiation.

36:16.409 --> 36:20.339
We do see a signature in the
rocks that indicate that there

36:20.338 --> 36:24.608
was an amount of carbon that was
oxidized at that point equal to

36:24.606 --> 36:28.126
several times the current
biomass of the planet.

36:28.130 --> 36:32.560
So carbon levels really dropped.

36:32.559 --> 36:36.319
I didn't list it here,
but I believe that at the end

36:36.315 --> 36:40.285
of this process the percentage
of oxygen in the earth's

36:40.291 --> 36:42.281
atmosphere is about 7%.

36:42.280 --> 36:45.840
Well that's as though I took
you suddenly in an elevator

36:45.844 --> 36:48.184
right to the top of Mount
Everest;

36:48.179 --> 36:51.509
that's hard to deal with.

36:51.510 --> 36:54.990


36:54.989 --> 37:00.029
Okay, that's one of the more
plausible hypotheses for the

37:00.030 --> 37:02.280
end-Permian extinction.

37:02.280 --> 37:06.650
The Cretaceous extinction is at
just about 65 million years ago;

37:06.650 --> 37:09.030
slightly less,
63 and a half,

37:09.032 --> 37:10.992
64 million years ago.

37:10.989 --> 37:15.089
And we do know that there was a
big meteorite that hit the

37:15.092 --> 37:17.542
Yucatan right at the right time.

37:17.539 --> 37:19.989
It probably did trigger
extinctions.

37:19.989 --> 37:22.519
Mechanisms aren't completely
clear.

37:22.518 --> 37:24.348
It wasn't necessarily the sole
cause.

37:24.349 --> 37:27.609
That meteorite in the Yucatan
could have set off massive

37:27.610 --> 37:30.340
volcanism in India,
and the reason is this:

37:30.340 --> 37:33.140
The earth is a spherical lens,
and if you throw a big rock

37:33.137 --> 37:36.297
into one side of the earth,
the energy from the impact

37:36.295 --> 37:38.825
radiates out,
reflects off the walls of the

37:38.829 --> 37:40.719
earth,
and comes back together at a

37:40.724 --> 37:42.404
single point on the other side.

37:42.400 --> 37:46.230
That single point on the other
side was focused into western

37:46.226 --> 37:49.916
India, at the time that India
was moving across the Indian

37:49.923 --> 37:51.873
Ocean, before it hit Asia.

37:51.869 --> 37:54.109
It was just in the right spot,
on the other side.

37:54.110 --> 37:57.000
And that's where those lava
flows are, and those lava flows

37:57.003 --> 37:58.503
have exactly the right date.

37:58.500 --> 38:01.300
So there's some reason to think
that this might actually have

38:01.304 --> 38:01.824
happened.

38:01.820 --> 38:05.360
If you go to the Hindu and
Buddhist cave temples of the

38:05.358 --> 38:08.498
Western Ghats in India,
you will be in those lava

38:08.503 --> 38:09.163
flows.

38:09.159 --> 38:14.339
They are massively thick and
they cover a huge area.

38:14.340 --> 38:18.380
So that's not demonstrated,
but certainly the meteorite is

38:18.382 --> 38:19.662
well-documented.

38:19.659 --> 38:22.509
It probably looked something
like this.

38:22.510 --> 38:27.510
So this is about a 30 kilometer
wide meteorite.

38:27.510 --> 38:31.640
It's coming in probably at
about 100,000 miles an hour,

38:31.644 --> 38:36.244
and of course it completely
fragments and sends up ejecta.

38:36.239 --> 38:41.179
And since it's hitting into a
shallow sea, it sends up a large

38:41.182 --> 38:43.292
tsunami, a mega-tsunami.

38:43.289 --> 38:47.799
There is evidence in Texas and
Oklahoma that the waves crossing

38:47.802 --> 38:52.462
the southern coast of the United
States at that point were one to

38:52.461 --> 38:54.211
two kilometers high.

38:54.210 --> 38:59.140
So a big event;
and burning debris rains down

38:59.135 --> 39:00.575
across the planet.

39:00.579 --> 39:03.819
If you go to Mexico now,
you can see the outer ring of

39:03.824 --> 39:04.624
the crater.

39:04.619 --> 39:08.379
It's a series of freshwater
wells in the cracked limestone

39:08.376 --> 39:10.086
pavement of the Yucatan.

39:10.090 --> 39:14.530
If you look with geological
probes under water,

39:14.532 --> 39:18.012
you can see the rim of the
crater.

39:18.010 --> 39:22.130
This is a distance here of
about 200 miles across.

39:22.130 --> 39:23.500
It's a big crater.

39:23.500 --> 39:28.530
So this is Simon Conway
Morris's reconstruction of what

39:28.527 --> 39:29.457
happens.

39:29.460 --> 39:32.420
Of course, when the rock falls
on your head,

39:32.418 --> 39:34.758
everything's killed right
there.

39:34.760 --> 39:37.250
There are giant earthquakes.

39:37.250 --> 39:40.540
Then within ten minutes,
the rock falling out of the air

39:40.539 --> 39:43.289
ignites all of the forests of
North America.

39:43.289 --> 39:48.399
About ten hours later tsunamis
are pretty much covering the

39:48.402 --> 39:53.342
planet, taking out anything
within one kilometer vertical

39:53.338 --> 39:55.628
distance of the ocean.

39:55.630 --> 40:00.100
Probably the first extinctions
of things that have a broad

40:00.096 --> 40:03.776
geographic range are occurring
within a week.

40:03.780 --> 40:06.480
There's a very,
very dusty atmosphere for about

40:06.478 --> 40:10.118
nine months, and that induces a
nuclear winter that lasts about

40:10.117 --> 40:10.937
ten years.

40:10.940 --> 40:13.530
We know it probably didn't go
on much more than ten years,

40:13.534 --> 40:15.634
because the plants do not
notice this event.

40:15.630 --> 40:18.990
The animals get killed,
but the plants have a seed bank

40:18.985 --> 40:22.025
in the soil, and the seeds can
make it through.

40:22.030 --> 40:24.570
So the plants don't notice this
event very much.

40:24.570 --> 40:28.510
Continental vegetation starts
to recover.

40:28.510 --> 40:32.200
The planet is pretty much
covered with ferns for about

40:32.204 --> 40:36.184
1000 years, but within 1000
years we start getting forests

40:36.177 --> 40:38.267
back and things like that.

40:38.268 --> 40:47.748
Then it takes the deep water in
the ocean several thousand years

40:47.753 --> 40:49.713
to recover.

40:49.710 --> 40:53.970
It takes about 50 to 100,000
years for the oceans to become

40:53.974 --> 40:55.744
well oxygenated again.

40:55.739 --> 40:58.469
It's thought that some
populations of dinosaurs,

40:58.469 --> 41:01.049
some places in the world,
managed to go on for about

41:01.052 --> 41:03.932
another 100,000 years,
before they all died out,

41:03.934 --> 41:07.044
and that the ammonites,
the last ammonites went out

41:07.039 --> 41:09.929
about 300,000 years later;
and then you can see the rest

41:09.929 --> 41:10.799
of this going on.

41:10.800 --> 41:14.860
It took about 15 to 25 million
years after the extinction to

41:14.856 --> 41:18.776
repopulate the planet to the
level of biodiversity it had,

41:18.775 --> 41:22.475
before the meteorite hit;
and that is an estimate of how

41:22.478 --> 41:26.008
long it might take the planet to
recover from the current human

41:26.010 --> 41:29.530
caused mass extinction,
which is going to be roughly an

41:29.534 --> 41:33.254
extinction of the same size as
one caused by a meteorite.

41:33.250 --> 41:36.020
This is just a bit of evidence.

41:36.018 --> 41:38.208
This is a section--I'm not
going to run through all of

41:38.213 --> 41:40.453
this, I just wanted you to have
this, if you wanted to,

41:40.449 --> 41:42.189
so you could see some of the
evidence.

41:42.190 --> 41:48.160
This is a deep sea core off of
the Florida Coast,

41:48.159 --> 41:51.629
and it marks the boundary
between the Cretaceous and the

41:51.632 --> 41:54.952
Tertiary,
and in this chunk of it right

41:54.954 --> 41:59.454
here are the impact ejecta;
so there is basically glassy,

41:59.445 --> 42:03.405
tectite globules and things
like that, and shocked quartz,

42:03.405 --> 42:04.165
in here.

42:04.170 --> 42:08.160
And the iridium--the famous
iridium anomaly--

42:08.159 --> 42:10.639
iridium is enriched in
meteorites and poor on the

42:10.637 --> 42:13.457
earth's surface,
and you pick up a lot of that

42:13.460 --> 42:14.920
element right in here.

42:14.920 --> 42:17.370
So this is the kind of evidence
from around the world that

42:17.367 --> 42:18.997
indicates that this was a big
event.

42:19.000 --> 42:22.380
So that's the end-Cretaceous
extinction, and it seems to be

42:22.382 --> 42:25.142
linked to the meteorite;
and may not only have been

42:25.137 --> 42:27.417
caused by the meteorite,
there were also volcanic

42:27.420 --> 42:28.040
eruptions.

42:28.039 --> 42:32.279
I'd now like to do a little bit
of local catastrophe--

42:32.280 --> 42:34.600
this is on a more frequent
timescale--

42:34.599 --> 42:37.539
just to convince you that
sometimes,

42:37.539 --> 42:42.359
on a shorter time period,
conditions are quite unusual.

42:42.360 --> 42:47.090
So major earthquakes;
I mean, we've all experienced,

42:47.085 --> 42:51.095
in 2006, the big tsunami in
Indonesia.

42:51.099 --> 42:52.739
There's several of those per
century.

42:52.739 --> 42:56.669
We haven't really had a
volcanic eruption in our

42:56.673 --> 43:01.783
lifetimes that came anywhere
close to Santorini or Tambora.

43:01.780 --> 43:04.980
Krakatoa was much smaller than
Tambora;

43:04.980 --> 43:07.530
and these things caused
tsunamis and global cooling.

43:07.530 --> 43:12.590
Then there are the gigantic
eruptions.

43:12.590 --> 43:16.220
Eruptions that were occurring
in the Cascade Mountains during

43:16.215 --> 43:19.835
the Pliocene would do things
like drop clouds of volcanic ash

43:19.842 --> 43:23.472
onto wandering herds of wooly
rhinoceroses in Nebraska,

43:23.469 --> 43:25.699
2000 miles away.

43:25.699 --> 43:28.949
And when the Phlegrean Fields
at Naples went up,

43:28.952 --> 43:31.722
they dropped ash into Kiev,
in Russia.

43:31.719 --> 43:35.219
The Phlegrean Fields are still
active, and they're a rather

43:35.222 --> 43:38.062
heavily populated suburb of
Naples right now.

43:38.059 --> 43:40.929
As a property owner,
you have to kind of wonder what

43:40.932 --> 43:42.062
you're sitting on.

43:42.059 --> 43:47.739
These come fairly rarely,
every 10,000 to 1000,000 years.

43:47.739 --> 43:50.489
Then there are undersea
landslides, and these can

43:50.492 --> 43:52.272
produce really huge tsunamis.

43:52.268 --> 43:56.588
So if the Nile Delta,
or the Mississippi River Delta,

43:56.590 --> 43:59.610
or the Amazon Delta loses
structural stability and sloughs

43:59.610 --> 44:02.660
off into deep water,
dropping cubic kilometers of

44:02.657 --> 44:05.607
sediment at one go,
you get a very big tsunami.

44:05.610 --> 44:06.720
I'll show you one in a minute.

44:06.719 --> 44:07.699
Okay?

44:07.699 --> 44:10.199
And then there are super
floods, and we've had some of

44:10.195 --> 44:11.605
those in Eastern Washington.

44:11.610 --> 44:13.530
They've occurred in Siberia and
Manitoba.

44:13.530 --> 44:16.680
They happen at the ends of Ice
Ages, when the glaciers are

44:16.677 --> 44:17.227
melting.

44:17.230 --> 44:20.810
So here is an example of a mega
tsunami,

44:20.809 --> 44:25.079
and this is what happened when
the West Coast of the Island of

44:25.079 --> 44:28.789
Hawaii fell into the water about
125,000 years ago.

44:28.789 --> 44:32.049
It dropped a chunk of rock that
was probably about 20 kilometers

44:32.054 --> 44:33.904
wide,
by about 1 or 2 kilometers

44:33.902 --> 44:35.832
deep, by about 8 kilometers
high,

44:35.829 --> 44:39.299
onto the floor of the ocean,
and by the time it had gotten

44:39.298 --> 44:41.738
this far,
it was moving 500 kilometers

44:41.737 --> 44:45.317
per hour,
and it shoved blocks of island

44:45.320 --> 44:50.660
that were about 1 kilometer long
out into deep water,

44:50.659 --> 44:52.239
about 200 kilometers away.

44:52.239 --> 44:55.879
And that's just about the right
velocity, in that depth of

44:55.882 --> 44:57.802
ocean, to entrain a tsunami.

44:57.800 --> 45:02.650
And this is a geological model
of how high this tsunami was.

45:02.650 --> 45:07.590
So the landslide is here,
and then the tsunami goes out;

45:07.590 --> 45:11.250
it actually goes well up into
the top of Lanai here.

45:11.250 --> 45:13.230
This is in meters.

45:13.230 --> 45:16.850
So when you start getting red,
you are up at 1000 feet above

45:16.853 --> 45:17.593
sea level.

45:17.590 --> 45:21.310
The highest point of the run-up
of this tsunami was right here

45:21.306 --> 45:22.156
at Ho'okena.

45:22.159 --> 45:26.149
It went up 2400 feet,
according to that.

45:26.150 --> 45:27.940
And there had been previous
ones;

45:27.940 --> 45:30.600
other pieces of island had
fallen off at various points.

45:30.599 --> 45:35.349
There is a ring of coral that
goes up to about 1500 feet

45:35.347 --> 45:37.967
elevation,
right here, from an earlier

45:37.965 --> 45:40.235
tsunami,
and perched on top of the

45:40.240 --> 45:44.580
island of Lanai is a lake of sea
water that was deposited on top

45:44.579 --> 45:47.659
of the island,
by a mega tsunami.

45:47.659 --> 45:51.309
So sometimes the surf is really
up.

45:51.309 --> 45:54.659
These are big waves.

45:54.659 --> 45:58.369
This is a recent volcanic
eruption, just to show you what

45:58.367 --> 45:59.227
it will do.

45:59.230 --> 46:03.240
This is pumping an awful lot of
ash into the atmosphere.

46:03.239 --> 46:07.019
This is at 22 kilometers
elevation, and this actually

46:07.018 --> 46:11.008
caused global cooling and
beautiful sunsets for a couple

46:11.014 --> 46:11.964
of years.

46:11.960 --> 46:15.810
And then these are the super
floods of eastern Washington

46:15.806 --> 46:18.346
that went down the Columbia
River,

46:18.349 --> 46:22.889
about a kilometer high,
and took an awful lot of the

46:22.891 --> 46:25.831
soil of eastern Washington off.

46:25.829 --> 46:29.389
And that's what happened when a
giant lake suddenly caused a

46:29.385 --> 46:32.155
glacial dam to burst and the
flood went out.

46:32.159 --> 46:32.859
Okay?

46:32.860 --> 46:36.600
This is the kind of a boulder
that could be easily moved by a

46:36.597 --> 46:37.717
flood that size.

46:37.719 --> 46:41.709
So basically the idea of this
lecture was to show you that

46:41.710 --> 46:45.560
life changed the planet,
and mainly it was bacteria that

46:45.559 --> 46:48.469
did it;
that the planet and the

46:48.469 --> 46:53.399
extraterrestrial environment
have had occasional major

46:53.402 --> 46:55.172
impacts on life.

46:55.170 --> 46:58.320
This big picture view,
this macroevolutionary view,

46:58.324 --> 47:02.304
describes a world that's really
qualitatively different from our

47:02.300 --> 47:03.690
normal experience.

47:03.690 --> 47:07.010
And we're going to reconstruct
what happened to some of those

47:07.014 --> 47:09.234
things next time in the fossil
record.

47:09.230 --> 47:14.230