18. Major Events in the Geological Theatre


Prof: Now today we’re
going to be talking about some of the major events in the
geological theater. This is the second of three
ways that we’re looking at the history of life.
The first was rather abstract;
it had to do with major transitions and with
reorganization of genetic information, units of selection,
things like that. That was last time.
Today we’re going to talk about
how life shaped the planet and how the planet shaped life.
So this is a quick run through
a 4.5 billion year process. And then next time we’re going
to talk about major lessons from the fossil record.
There are a lot of ways of
trying to construct a diagram that will give you a feel for
deep time, and it’s not so easy. I once did a kindergarten class
where I took a bunch of kindergartners and I tried to
get them to step off 100 million years at a time,
or 10 million years at a time. I think I did 10 million years
so that we could take six steps and then meet a dinosaur.
And there are a lot of ways of
doing this, but this is not a bad one
because it gives you a diagram that shows you about how much of
the existence of the planet has been occupied by life;
about how much of it has been a story that’s mostly of
prokaryotes, in other words about half of
the time that life has been on the planet,
there have only been prokaryotes;
and about how much of it has been complicated multicellular
organisms. And, of course,
we show up just briefly before midnight, on that kind of a
scale. So that’s one way of looking at
it. And learning to think about
deep time is really important if you have a taste for
macroevolution, and it’s certainly important if
you have a taste for geology. Now, at the beginning,
we had a reducing atmosphere, and the source of O2 was
photosynthetic bacteria. I’m just going to check
something here; yes, okay.
So we start off with a reducing
atmosphere, and then we have to fill up
essentially, once the photosynthetic
bacteria get going– and, by the way,
some of them were chemosynthetic as well as
photosynthetic– once the photosynthetic
bacteria get going and start producing a lot of oxygen,
there’s a tremendous mass of stuff on the face of the earth
that has to be oxygenated before there’s any free oxygen.
So that takes quite awhile.
So until about half of the age
of the planet, the concentration of oxygen in
the atmosphere was less than 0.4%.
You would all die within a
minute, at that oxygen concentration.
And the evidence that we have
of when there was free oxygen in the atmosphere is essentially
the age of the iron mines of the world.
So there was ferrous oxide–it
can dissolve in water– floating around in the ocean,
and when the oxygen level of the atmosphere got high enough,
it oxidized to ferric oxide, and the ferric oxide fell out
of solution, and when it fell out of
solution it made the iron mines of the world.
That happened 2.3 billion years
ago. This kind of process continued
with other sorts of elements. So we have copper coming out at
about 1.7 billion years, at a higher concentration of
oxygen. And the consequences of free
oxygen are that an ozone layer forms in the atmosphere.
That screens ultraviolet light
and that drops the mutation rate,
and it’s probably only because the mutation rate dropped
significantly with an ozone layer that we could evolve large
long-lived organisms. Once you have oxygen in the
atmosphere, you can start getting nitrates.
Nitrates are oxygenated
nitrogen. So you won’t really have
nitrogen fertilizer until you have free oxygen,
and that then also became a key nutrient for algae.
So there’s a whole sequence of
important chemistry that goes on over a period of about 3 billion
years that starts to set up the environment that we’re familiar
with. There are a number of ways of
looking at this. This is from Don Desmirais,
at the Ames Research Center. He’s an astrobiologist and has
specialized in trying to examine the question of life on other
planets; and they have tried to make
diagrams like this for other planets as well.
So in our early environment,
the sun was only about 70% as hot as it is now,
and by about 500 million year ago it was up to 95%.
The early environment of the
earth was a meteorite bombardment.
So if you were out looking at
the night sky– which, of course,
you wouldn’t have been able to do because the meteorite
bombardment was so intense that you would’ve been standing on a
boiling lake of lava– but, if you were out,
looking at the night sky, on your boiling lake in lava,
in your terminator suit or whatever,
you would’ve seen lots and lots of big meteorites coming in
every night; and that gradually tailed off.
Okay?
The heat flow out of the molten
mass forming the core of the earth has tended to drop off and
stabilize. So it has a continuous
radioactive input, but the original heat from the
entire planet being molten has gradually radiated.
So we’re stabilizing at about
the heat flow from the radioactivity in the earth.
And the continents formed and
stabilized at about 1.8 to 2 billion years ago,
and these things called major orogenies are major chunks of
continent coming up and major mountain ranges getting built.
Now the collision of plate
tectonics has continued to form mountain ranges since then,
but this just stabilizing the continental crust took about 2
billion years. If you look at the history of
the atmosphere, of course we’re currently
worried about the costs: carbon taxes,
and global warming, and anthropogenic effects on
the CO2 concentration in the atmosphere.
But at the origin,
the CO2 level was much, much higher.
The atmosphere was more than
what we would call 100% CO2, because it was thicker at that
point, and it blew off. This has dropped down here to
about 3 times 10^(-4) atmospheric pressure for CO2.
It’s actually a small component.
Oxygen rose and probably
reached present levels at about 5 or 600 million years ago.
It’s interesting that if it
went up a little bit more, a room like this could catch on
fire, just spontaneously. At about 27%,
wood will catch on fire spontaneously,
at current atmosphere pressures.
So this is another way of
looking at that process. At the beginning,
we had water, hydrogen, carbon monoxide,
lots of steam; a lot of that escaped to space.
There were meteorite impacts.
The CO2 curve has gone down.
The oxygen curve has done up;
there’s some indications it’s gone up stepwise.
Temperature,
we don’t really know accurately what the temperature was back
before 3.5 billion years, but we can be pretty sure that
at and after the origin of life, water was liquid on the surface
of the planet; so that sets an upper limit of
100 degrees Centigrade. And temperature has gone up and
down in a number of cycles over a fairly long period,
and there have been some major Ice Ages.
How do you recover that?
Well one of the ways that you
can do it is you can look, if you have leaves of fossil
plants– so if you’ve already got plants
that evolved and they have leaves;
so maybe about the last 300 million years or so–you can
look at the stomatal ratios on them.
So this has been calibrated.
Plants have to make more holes
in their leaves; if there’s less carbon,
they have to have a bigger mouth so that they can feed more
efficiently. And they can have fewer holes
in their leaves if–and they can be smaller–if there’s more
carbon in the atmosphere. And so basically this allows
you to plot and estimate a curve.
And it looks like there was
massive withdrawal of carbon dioxide from the atmosphere from
the Ordovician, through the Permian,
right here. And then there was a
re-injection here, going into the Triassic–and
when we come to the Permian Mass Extinction,
I want you to remember this dip here,
and this re-injection–and then there’s been a more gradual
withdrawal down to the current level.
So the earth was much more of a
greenhouse in the past than it is today.
And if we look at where the
carbon dioxide went, a lot of it got locked up in
limestone, in sedimentary rock. Then a lot of it is in organic
carbon. A lot of it is in the ocean,
is bicarbonate. These are by far the largest
sinks, but there’s a lot of bicarbonate ion in the ocean.
This is all the fossil fuel on
the planet right here; so this is all the coal and oil.
And you can see that of the
original amount of carbon that was in the earth’s atmosphere,
that’s a pretty small fraction; it’s a bit less than
1/1000^(th) of 1%. And in living biomass,
there’s a very, very small part.
So basically if you look at
that, you can see that the carbon balance of the planet is
extremely dependent upon what happens in rocks,
and that if there are small geological changes in the cycle
of how carbon is going in and out of rock,
and whether it’s being subducted as plate tectonics
proceeds or not, is going to make a much bigger
difference to the amount of carbon in the atmosphere than
the amount of fossil fuel that’s being burned,
or the tree cover of the planet in forests,
which would be the living biomass term down here.
However, this is a slow
process, and this is a fast process.
So on the scale of human
lifespans, this is in fact more important.
But on the scale of say
somewhere out at around 100,000, out into the millions of years,
what’s happening in sedimentary rock is really critical.
Now if we look at the way that
life structures the planet, one of the very important
things that life has done is that it’s made soil.
And we don’t really start to
get soil, which is a big complicated
piece, an engineered niche that plants create,
until we get complicated plants on land.
So the first ones on land are
probably things like liverworts, and our first fossils are club
mosses, and that’s happening back at
around 400 to 500 million years ago.
There are fossil soils,
and those fossil soils have roots in them,
and those roots suggest that the first time that there were
real trees was at about 350 to 400 million years ago.
Remember back to that clock.
This is relatively recent,
in terms of the age of the planet.
So we get really modern soils
with layering, and with evidence of seed
plants in the Carboniferous. So that is the age at which
most of the coal mines of the earth were laid down;
it’s about 300 million years ago.
If you take Interstate 80,
west of New York, and you go out to where it
crosses from New Jersey into Pennsylvania,
at the Delaware Water Gap, there’s a cut there that you
can look up at, and what you’re looking at is
the outwash of rivers that were coming down off of the Taconic
mountain range. And if you look into that cut,
it’s remarkably clean. It’s a preservation of what was
coming down rivers 500 million years ago, and it’s an
indication that there was very little soil.
It is basically at or before
this process occurs. And that mountain range was
formed when Pangaea formed, which is at around 550 to 600
million years ago, and caused the Taconic orogeny,
and that put up a mountain range on the border between
Connecticut and New York that was about as high as the
Himalayas, but it didn’t have any forests
on it, and it had a very high erosion
rate because there weren’t plants to stabilize the soil.
And we can see,
in the Delaware Water Gap, what washed off that mountain
range. It’s all worn down now,
and if we come back in another 500 million years,
the Himalayas will all be worn down.
But, with the Himalayas,
there will be a bit more soil in the outwash.
The guys that have really in
the past engineered the planet, and that continue to do so,
are the bacteria; and by that I mean both the
archaea and the eubacteria. They are the ones that play a
huge role in the carbon cycle. They’re producing and
oxygenating methane. They’re fixing carbon dioxide.
In the nitrogen cycle,
the bacteria are fixing nitrogen from the atmosphere;
they fix it as ammonia. They oxygenate ammonia to
nitrate; they de-nitrify nitrates to
ammonia. And this is a kind of
biochemistry that just about nobody else has.
So these are essential things;
the nitrogen in all of the proteins on the planet is
essentially originating through bacterial processes.
So that’s how it’s getting from
the abiotic world into the living world.
There are sulfur bacteria that
are arguably extremely ancient, and which evolved in an
environment in which much of the energy coming into living
systems was coming from things like sulfur,
rather than from sunlight, and they oxidize hydrogen
sulfide to sulfate; they reduce sulfate to hydrogen
sulfide. And iron bacteria are
converting ferrous to ferric iron, and they’re influencing a
degradation of manganese and copper deposits.
A lot of this is now going on
at spreading centers at mid-ocean ridges,
or it is going on where there is heat flow which is taking
ocean water through the ocean crust,
and there are bacteria that are sitting just below the ocean
crust that are sitting in a stream of basically hot chemical
soup that’s coming through, and when they do these
reactions, often they leave a metal deposit behind;
which is why the floor of the Pacific Ocean is covered with
manganese nodules that people are thinking about mining at a
depth of about five kilometers. If you go down into the earth’s
crust, it turns out that the biosphere extends below our feet
several kilometers; bacteria are active that far
down into the soil, and they are carrying out
things like this. So they are really key players
in structuring the environment in which we live,
and they do a lot of services that we simply take for granted
and frankly hadn’t even noticed until about the last hundred
years of so. Okay, so those are all aspects
of how life has modified the planet.
How has the planet modified
life? Well there are at least three
or four big chapters here. One is through continental
drift; another is glaciation;
mass extinction; and then local catastrophes.
And continental drift and mass
extinctions are both out there at the scale of hundreds of
millions of years. Glaciation has two scales.
There are times in the planet’s
history when it’s been relatively cold;
basically there’ve been at least three times when it’s been
really quite cold. But within those longer periods
that are cold, the glaciers have come and gone
many times. So the North American
glaciation lasted 2.5 million years, and the glaciers came and
went about 15 times, in North America.
The local catastrophes,
it all depends on which particular kind that is.
You’ll see that they occur at
different time scales. The point of all of this is
that often the past configuration of the planet,
whether it’s the location of the continents,
or the temperature of the earth, or whether you could
expect to live in a secure environment,
have at times been extremely different from what we currently
see. And so it is not only
important, if you want to understand evolution,
to cultivate a sense of deep time, it’s also important to
cultivate a sense of different time;
sometimes deep time was really different, and that’s what I’m
trying to get at, by showing you these things.
So here’s the last 400 million
years of continental drift. And, by the way,
people are producing models that can now take this back to
about oh a billion years. Of course, the further you go
back, the harder it is to reconstruct
it, because the continents have
come together and come apart, and come together and come
apart, in a long-term cycle several times,
and in so doing they kind of wipe out the traces of their
history. So it’s really quite a feat to
try to reconstruct it. And I’d just like to point out
a couple of things here. This is Gondwana.
So Pangaea was a little bit
earlier than this; that was when all of the
continents were together. South America and Africa and
Antarctica and Australia stuck together–and India–stuck
together for awhile, before they came apart.
There is an interesting thing
going on right here. Here’s New Haven.
If you go out to Lighthouse
Park in New Haven, you’ll see some rocks there,
and if you trace where the closest relatives of those rocks
are, on the other side of the ocean,
they’re in Rabat, Morocco.
Okay?
So you can actually see the
same kind of rock on the other side of the ocean.
And that’s when that happened;
that’s 250 million years old. Anybody know how old East Rock
is? East Rock’s 225 million years
old. When the Atlantic opened–you
see the Atlantic opening here–there were a series of
rifts that opened up, one of which became the
Atlantic; another one became the
Connecticut River Valley. It didn’t open,
but it went part way, and then it had a valley
filling lava flow that filled it up,
and then the flow tipped, and it tipped pointing west,
and it cracked in a number of places,
and that’s what’s East Rock, West Rock,
and all the other such formations that go up through
central Massachusetts to southern Vermont.
That was a big lava flow;
filled up a big rift valley. So that happened right here.
Now when Gondwana split up,
it had some things living on it.
The ratite birds,
and they are flightless and they don’t swim,
and essentially they got rafted around on pieces of rock.
And it’s interesting,
if you think about when Gondwana split up,
it indicates that the ancestor of these birds was already alive
and living across that range of geography,
at that point. And you can lay a molecular
phylogeny of the ratites onto these continents and it just
ties them right together. Okay?
There’s another thing that
happened with the breakup of Pangaea.
Laurasia went north,
Gondwana went south. In between, for awhile,
there was a thing called the Tethys Sea.
And this is the configuration
of the continents about 50 million years ago,
in the Eocene. By the way, the Eocene was
quite warm; it was really a very tropical
period. And at that time there was
either– there was a warm kind of
Mediterranean coastline that stretched from eastern North
America, through Nepal,
what is now Nepal, into what is now eastern China.
This was before India rafted
north and Africa came north and closed off South Asia.
And this is what is thought to
have accounted for some of the similarities in the plants that
you find in the Appalachian Mountains and in China.
And there are many affinities
here. The rhododendrons, viburnum;
there are a number of tree species that share a
phylogenetic relationship across that huge geographical distance,
and it’s thought to have been the signature of a corridor
along which seeds could move 50 million years ago.
Now how about glaciers?
Well here is a fairly deep
timescale. So this is the Phanerozoic;
the Phanerozoic is the term for everything that’s happened since
the Cambrian started. So this is the Phanerozoic here.
So this is at about 500 million
years. This is about 600 million
years, and there’s evidence for one which is deeper,
at about a billion years. So this is an Ice Age,
this is an Ice Age. It looks there was an
Ordovician Ice Age, it looks like there was a
Permian Ice Age, and then there was an Ice Age
just in the Pleistocene. So about five Ice Ages.
Interestingly,
this one, which came before the Cambrian, may have been a time
when the earth was almost entirely covered with ice.
There are signatures you can
find in the rocks of what latitude you’re at,
whether you’re close to the equator or not,
and there are other signatures you can find in the rocks that
give you how cold it was. These are usually in the form
of isotope ratios for things like oxygen and carbon and stuff
like that. And at this point the entire
earth may have been a snowball, and only the things that were
very, very close to the equator may
have come through, because if it really was a
snowball, then there was ice covering the
world’s oceans. That is an interesting issue,
and it’s one that will probably cause people to speculate and
publish for quite awhile, because it’s so hard to
resolve; there’s not too much data,
it’s a long time ago. The Permian glaciation,
however, is much better studied.
Remember that in the Permian,
Gondwana is still together. It breaks up at about 225
million years ago; somewhere between 225 and 250.
Well the Permian is at 250;
about 251 I think. And there was a southern ice
cap that was on- actually connected, and actually these
continents were all together; and you can see from the arrows
the direction in which the ice was flowing.
And I think it’s really cool
that you can find rocks, from Africa,
that were scraped off by the glaciers and deposited in
Brazil. Before plate tectonics came
along, nobody had any idea how that could have happened.
And if you stand on the top of
Table Mountain, in Cape Town today–which is
something I recommend that any of you that have the opportunity
to go to Cape Town do; it’s really a very beautiful
place–you can still see the grooves in the rock from where
the glaciers moved over Cape Town;
they’re 250 million years old. The climate since then has
actually mostly been warm. So this, if you look on this
set of maps–this is 50 million years ago;
35 million years ago; 15 million years ago;
middle of the Pleistocene, about 1.5 million years ago;
and very close to today, mid-Holocene would be say about
5000 years ago– and you look at how much of the
planet is temperate and tropical,
look at how tropical the Eocene was.
That was all tropical
rainforest, and the Oligocene was still- there was still a
huge area of tropics, and the Miocene still had
pretty good tropics. But at the last glacial
maximums, the tropical rainforests were reduced to a
few patches. We’re living today in a
relatively cold, relatively dry world.
That’s what we think is normal.
If we were to come in a polar
orbiting satellite and look down at the planet say 20,000 years
ago, 30,000 years ago,
we would’ve seen that where we’re sitting right here is
under probably about a mile and a half of ice.
The leading edge of it is
pushing stuff off of the continent that becomes Long
Island and Block Island and Martha’s Vineyard and Nantucket;
that’s the terminal moraine of this glacier.
Scandinavia and Northern
England are completely under ice, as is the North Sea.
The Sahara Desert was humid.
You can go into the middle of
the Sahara Desert and you can see rock paintings that humans
made there, where they’re recording
hippopotamuses and things like that,
living in the middle of the Sahara,
at this time. And we’ll see in a minute that
the major tropical forests shrank.
So this is more or less the
global pattern. The grey now is ice.
The green is tropical forest.
The red and orange are–excuse
me, the green is grassland; the orange is rainforest.
So there are tropical forest
refugia, in certain places. And if you were to go into the
south, what is now the South China
Sea, which is currently covered by water,
elephants and tigers could walk out,
over that, because it was dry land–
enough water had been tied up in the ice to drop the sea level
down that much– and that is how they got to
Borneo. So they could actually just
move down from Asia and get out as far as Borneo,
but they couldn’t make it across Wallace’s Line–
there is a deep-water passage there that Alfred Russel Wallace
documented in the biogeography of Indonesia–
and they couldn’t make it to Australia or New Guinea.
So the sea level has gone up
and down, and that’s changed continental margins and the
ability of things to move around in them.
So that’s impact of glaciations.
What about mass extinctions?
There’ve been two biggies,
end-Permian and end-Cretaceous. And at the end of the Permian
not only did the trilobites disappear,
but in fact the estimate is that 97% of all marine
invertebrate species disappeared at the end of the Permian.
That is an extremely close
brush with sterilizing the planet;
it came pretty close. At the end of the Cretaceous
the things that disappeared, that we probably would like to
have around to look at, if we possibly
could–ammonites, dinosaurs–
almost everything that lived on land,
that was bigger than five kilos, went extinct,
and about 70% of the marine invertebrate species went
extinct. So this was a big one,
but the biggest was the Permian extinction.
So these are the trilobites.
They had been around since the
late-Cambrian– mid-Cambrian to
late-Cambrian–so they had been around for about 250 million
years, and they went extinct at the
end of the Permian. And these are ammonites.
In fact, the chambered nautilus
is fairly close to being an ammonite;
it would be sort of a modern survivor of this lineage.
So they were squid-like
creatures that had curved shells.
And if we look at the diversity
curve for–so this is the number of families that you could find;
these are mostly marine invertebrate families.
Okay?
So the number of families of
organisms. This scale goes from 0 up to
about 1000. This is the beginning of the
Cambrian, right here. This is the Vendian,
and then the Cambrian begins here.
This is the Ordovician,
the Silurian, Devonian, Carboniferous,
Permian, Triassic, Jurassic, Cretaceous,
Tertiary. So this is the Age of Dinosaurs
here; this is the Age of Mammals here.
And you can see that most of
the last 550 million years of history is a history of marine
invertebrates. This is a mass extinction at
the Ordovician. This is a mass extinction at
the Devonian. This is the Permian mass
extinction, and this is the Cretaceous mass extinction.
The red is the modern fauna,
the green is the Cambrian creatures, and the blue is the
stuff that originated in the Paleozoic.
So you can see that we still
have–almost all the Cambrian things are gone.
We still have families of
things that originated in the Paleozoic,
and what we think of as the modern creatures really started,
some of them started way back in the Cambrian,
but they built up a lot in the Carboniferous and Permian,
and then radiated again in the Triassic.
So what caused that big
extinction? Well Gondwana was breaking up,
and so–Laurasia was also separating from Gondwana–so
Pangaea was breaking up. At that time there was
large-scale volcanism, and at that time there was a
lack of oxygen in the oceans. If you go to the Black Sea
today–the Black Sea is sort of the model for what this ocean
looked like. The top oh twenty meters or so
of the Black Sea is oxygenated and has fish in it.
The Black Sea at its deepest
point is about two miles deep, and everything from twenty
meters, down to the bottom of the ocean,
is anoxic, and it stinks like rotten eggs.
Okay?
Imagine the entire world’s
ocean being in that state: a very thin,
oxygenated, clear upper layer; and everything below it
basically anoxic: no vertebrates can live in it;
it’s dominated by bacteria; and it stinks like rotten eggs.
Some people have suggested that
there were extraterrestrial influences at the time.
It’s been difficult to find a
meteorite crater of exactly the right age.
It doesn’t mean there aren’t
any–absence of evidence is not evidence of absence–
but plate tectonics has remodeled the surface of the
planet extensively since then, and it’s quite possible that
there was a big meteorite crater but it got subducted and it’s
been erased, so that we can’t see it.
At any rate,
this is a fertile area for speculation,
and people have thought of asteroids,
comets and supernovas that might have affected the planet
at the end of the Permian. It seems likely that it’s the
breakup of the continents and large-scale volcanism,
but I can’t really claim that we really know what caused the
extinction. If you go to Siberia,
you can find what are called the Siberian traps.
These are among the largest
flood basalt lava flows on the planet, and they have just the
right age; they’re at about 251 million
years. And we know that the extinction
lasted not too long; it was a few 10,000 years.
It happened both on land and in
the oceans, and the organisms that went out
in the oceans were the ones that were particularly susceptible to
changes in the gas regime. So that would suggest very high
CO2 levels. So one idea is this:
there were massive volcanic outbreaks in Siberia.
That caused global warming.
That global warming then
triggered the release of a huge amount of methane that was
stored in the ocean. Okay?
This is this Black Sea-like
world ocean. The methane then gets oxidized
to carbon dioxide, and essentially extinctions
happen by poisoning and asphyxiation.
We do see a signature in the
rocks that indicate that there was an amount of carbon that was
oxidized at that point equal to several times the current
biomass of the planet. So carbon levels really dropped.
I didn’t list it here,
but I believe that at the end of this process the percentage
of oxygen in the earth’s atmosphere is about 7%.
Well that’s as though I took
you suddenly in an elevator right to the top of Mount
Everest; that’s hard to deal with.
Okay, that’s one of the more
plausible hypotheses for the end-Permian extinction.
The Cretaceous extinction is at
just about 65 million years ago; slightly less,
63 and a half, 64 million years ago.
And we do know that there was a
big meteorite that hit the Yucatan right at the right time.
It probably did trigger
extinctions. Mechanisms aren’t completely
clear. It wasn’t necessarily the sole
cause. That meteorite in the Yucatan
could have set off massive volcanism in India,
and the reason is this: The earth is a spherical lens,
and if you throw a big rock into one side of the earth,
the energy from the impact radiates out,
reflects off the walls of the earth,
and comes back together at a single point on the other side.
That single point on the other
side was focused into western India, at the time that India
was moving across the Indian Ocean, before it hit Asia.
It was just in the right spot,
on the other side. And that’s where those lava
flows are, and those lava flows have exactly the right date.
So there’s some reason to think
that this might actually have happened.
If you go to the Hindu and
Buddhist cave temples of the Western Ghats in India,
you will be in those lava flows.
They are massively thick and
they cover a huge area. So that’s not demonstrated,
but certainly the meteorite is well-documented.
It probably looked something
like this. So this is about a 30 kilometer
wide meteorite. It’s coming in probably at
about 100,000 miles an hour, and of course it completely
fragments and sends up ejecta. And since it’s hitting into a
shallow sea, it sends up a large tsunami, a mega-tsunami.
There is evidence in Texas and
Oklahoma that the waves crossing the southern coast of the United
States at that point were one to two kilometers high.
So a big event;
and burning debris rains down across the planet.
If you go to Mexico now,
you can see the outer ring of the crater.
It’s a series of freshwater
wells in the cracked limestone pavement of the Yucatan.
If you look with geological
probes under water, you can see the rim of the
crater. This is a distance here of
about 200 miles across. It’s a big crater.
So this is Simon Conway
Morris’s reconstruction of what happens.
Of course, when the rock falls
on your head, everything’s killed right
there. There are giant earthquakes.
Then within ten minutes,
the rock falling out of the air ignites all of the forests of
North America. About ten hours later tsunamis
are pretty much covering the planet, taking out anything
within one kilometer vertical distance of the ocean.
Probably the first extinctions
of things that have a broad geographic range are occurring
within a week. There’s a very,
very dusty atmosphere for about nine months, and that induces a
nuclear winter that lasts about ten years.
We know it probably didn’t go
on much more than ten years, because the plants do not
notice this event. The animals get killed,
but the plants have a seed bank in the soil, and the seeds can
make it through. So the plants don’t notice this
event very much. Continental vegetation starts
to recover. The planet is pretty much
covered with ferns for about 1000 years, but within 1000
years we start getting forests back and things like that.
Then it takes the deep water in
the ocean several thousand years to recover.
It takes about 50 to 100,000
years for the oceans to become well oxygenated again.
It’s thought that some
populations of dinosaurs, some places in the world,
managed to go on for about another 100,000 years,
before they all died out, and that the ammonites,
the last ammonites went out about 300,000 years later;
and then you can see the rest of this going on.
It took about 15 to 25 million
years after the extinction to repopulate the planet to the
level of biodiversity it had, before the meteorite hit;
and that is an estimate of how long it might take the planet to
recover from the current human caused mass extinction,
which is going to be roughly an extinction of the same size as
one caused by a meteorite. This is just a bit of evidence.
This is a section–I’m not
going to run through all of this, I just wanted you to have
this, if you wanted to, so you could see some of the
evidence. This is a deep sea core off of
the Florida Coast, and it marks the boundary
between the Cretaceous and the Tertiary,
and in this chunk of it right here are the impact ejecta;
so there is basically glassy, tectite globules and things
like that, and shocked quartz, in here.
And the iridium–the famous
iridium anomaly– iridium is enriched in
meteorites and poor on the earth’s surface,
and you pick up a lot of that element right in here.
So this is the kind of evidence
from around the world that indicates that this was a big
event. So that’s the end-Cretaceous
extinction, and it seems to be linked to the meteorite;
and may not only have been caused by the meteorite,
there were also volcanic eruptions.
I’d now like to do a little bit
of local catastrophe– this is on a more frequent
timescale– just to convince you that
sometimes, on a shorter time period,
conditions are quite unusual. So major earthquakes;
I mean, we’ve all experienced, in 2006, the big tsunami in
Indonesia. There’s several of those per
century. We haven’t really had a
volcanic eruption in our lifetimes that came anywhere
close to Santorini or Tambora. Krakatoa was much smaller than
Tambora; and these things caused
tsunamis and global cooling. Then there are the gigantic
eruptions. Eruptions that were occurring
in the Cascade Mountains during the Pliocene would do things
like drop clouds of volcanic ash onto wandering herds of wooly
rhinoceroses in Nebraska, 2000 miles away.
And when the Phlegrean Fields
at Naples went up, they dropped ash into Kiev,
in Russia. The Phlegrean Fields are still
active, and they’re a rather heavily populated suburb of
Naples right now. As a property owner,
you have to kind of wonder what you’re sitting on.
These come fairly rarely,
every 10,000 to 1000,000 years. Then there are undersea
landslides, and these can produce really huge tsunamis.
So if the Nile Delta,
or the Mississippi River Delta, or the Amazon Delta loses
structural stability and sloughs off into deep water,
dropping cubic kilometers of sediment at one go,
you get a very big tsunami. I’ll show you one in a minute.
Okay?
And then there are super
floods, and we’ve had some of those in Eastern Washington.
They’ve occurred in Siberia and
Manitoba. They happen at the ends of Ice
Ages, when the glaciers are melting.
So here is an example of a mega
tsunami, and this is what happened when
the West Coast of the Island of Hawaii fell into the water about
125,000 years ago. It dropped a chunk of rock that
was probably about 20 kilometers wide,
by about 1 or 2 kilometers deep, by about 8 kilometers
high, onto the floor of the ocean,
and by the time it had gotten this far,
it was moving 500 kilometers per hour,
and it shoved blocks of island that were about 1 kilometer long
out into deep water, about 200 kilometers away.
And that’s just about the right
velocity, in that depth of ocean, to entrain a tsunami.
And this is a geological model
of how high this tsunami was. So the landslide is here,
and then the tsunami goes out; it actually goes well up into
the top of Lanai here. This is in meters.
So when you start getting red,
you are up at 1000 feet above sea level.
The highest point of the run-up
of this tsunami was right here at Ho’okena.
It went up 2400 feet,
according to that. And there had been previous
ones; other pieces of island had
fallen off at various points. There is a ring of coral that
goes up to about 1500 feet elevation,
right here, from an earlier tsunami,
and perched on top of the island of Lanai is a lake of sea
water that was deposited on top of the island,
by a mega tsunami. So sometimes the surf is really
up. These are big waves.
This is a recent volcanic
eruption, just to show you what it will do.
This is pumping an awful lot of
ash into the atmosphere. This is at 22 kilometers
elevation, and this actually caused global cooling and
beautiful sunsets for a couple of years.
And then these are the super
floods of eastern Washington that went down the Columbia
River, about a kilometer high,
and took an awful lot of the soil of eastern Washington off.
And that’s what happened when a
giant lake suddenly caused a glacial dam to burst and the
flood went out. Okay?
This is the kind of a boulder
that could be easily moved by a flood that size.
So basically the idea of this
lecture was to show you that life changed the planet,
and mainly it was bacteria that did it;
that the planet and the extraterrestrial environment
have had occasional major impacts on life.
This big picture view,
this macroevolutionary view, describes a world that’s really
qualitatively different from our normal experience.
And we’re going to reconstruct
what happened to some of those things next time in the fossil
record.

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