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In this lecture, we learn about
relationships between cultural history,
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civilizations, and climate change.
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And we will see how we can identify
the changes from natural archives.
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All civilization occurred
during the full Holocene,
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the period of the last 10,000 years.
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But during that period, also,
climate, sea level changed and
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that had a lot of impact
on early civilizations.
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In big history, we try to place
human history in the broad context.
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And we like to explore how climate and
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sea level change has
influenced cultural history.
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And here we take the Maya
civilization as an example.
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And we like to know how climate
conditions in the past inside of Mexico
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has influenced the culture of the Mayas.
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The question now is,
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how can we gain knowledge of climate
conditions of thousands of years ago?
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Well, we use proxies, and
a proxy is information
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about what we like to know of the past but
what was never measured.
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So here we use the changing vegetation
as an indicator of climate change.
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So in this case vegetation change is our
proxy and it has information on climate.
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Vegetation change can be
monitored by pollen grains,
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for use by the flowers of the plants.
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And here in this book you see
illustrations of many different
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pollen grains.
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These are photographs taken
under the microscope.
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What is our archive,
well that can be a peat bog.
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Here you see a profile of about two and
a half meter high.
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And the oldest peat is at the bottom and
the youngest peat is at the top.
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And if you take a sample
through the peat core
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then you have a sample from old at
the bottom to young at the top.
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You can take samples
every five centimeter for
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example and
try to extract information from that.
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Another option is that you drill a core.
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And here you see a core of
sediments of one meter length.
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And every centimeter, we took a sample.
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And the total length here
reflects 6,000 years.
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So, every centimeter
makes a jump of 60 years.
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Here you see a sample of about one
cubic centimeter of sediment and
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this sample is prepared in the laboratory.
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And that means that we have here in this
glass tube a concentrate of pollen grains.
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All the rest has disappeared and only
the pollen grains are here in this tube.
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From the pollen grains,
we make a microscope slide.
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This is a microscope slide, and
this is analyzed under the microscope.
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Well, then we have the pollen manuals
to identify the pollen grains.
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And then finally we can calculate and
draw a pollen diagram.
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Here we see a pollen diagram
from northwest Europe.
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And along the vertical is the time, and
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on the horizontal are the different
herb species and tree species.
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And on top, you see how the pollen grains
look like, of all those different plants.
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The pollen diagram shows
the last 12,000 years.
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And at the bottom you see
the last part of the ice age.
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And the vegetation is dominated by herbs
and pioneer trees like pine and birch.
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And then we cross the blue line and
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then we arrive in the Holocene,
the period of the last 10,000 years.
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And then you see an increasing number of
species immigrating into northwest Europe.
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So the forest starts to be
more diverse and more complex.
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And at the top you see the most
recent part and there you see for
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example that beach is a tree that
only arrived about 2,800 years ago.
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Now we make a step from a pollen
diagram to a landscape.
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In the middle you see the vertical bar,
that is a bar of 100% white.
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And you see the changing
proportions of the different trees.
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So again at the bottom we
are in the lead glacial.
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And you see an open landscape
dominated by herbs.
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And then when we enter the Holocene
you see the trees immigrating.
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And you see that the landscape
starts to be more and more complex.
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Well in the middle of the figure and
then we are around 5,000 years ago,
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most species had arrived.
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And we talk about the climax first.
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And in the top two figures
you see that people had
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a significant impact on the landscape
by clearing the forest and
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by making agriculture.
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So you see in this diagram
how the climate has changed
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the vegetation, the forest composition.
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While at the same time man entered and
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started to change the landscape
because of their agriculture and
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all the space they needed for
their villages and their roads.
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Well now we make the step to the Mayas.
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And we go to Yucatan
in southern Mexico and
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Yucatan is geologically speaking,
a remarkable part of the world
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because it is a build up of limestone,
of calcium carbonate.
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Well, the Mayas lived there for some
2,000 years and they built huge cities.
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And you see many different buildings
here that must have been large cities.
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Most cities probably had
30,000 to 40,000 inhabitants.
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So that means that agriculture and
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the production of food is very
important to let these cities survive.
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But the limestone has a problem
because all the rain that comes in
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immediately disappears in the soil.
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So you see no rivers in the landscape,
the rivers are subterraneously.
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So you have to go down in the holes, so
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where the rocks has been
dissolved by rainwater.
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And you can walk down, 10, 20 meter and
there you see the rivers in the soil.
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The problem of a limestone is,
that at the surface it is always dry.
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So the vegetation is in the dryness
stress, and also the people.
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The people have to go down to
the subterraneous rivers to
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collect their water.
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So these areas of the world are very
prone to climatic droughts.
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And if you look at
the forest composition in
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this photograph then
you see a mixed forest.
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You see trees that keep their leaves and
that are green.
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And you see leaves that
have shed their leaves.
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So you see trees resistant to drought, and
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you see trees that are not
resistant to drought.
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It is a mix here and that is evidence
that the climate is seasonal.
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There's humid,
very dry intervals during the year.
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This is a pollen diagram
from Lake Coba in Yucatan.
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And you see the lake itself, and
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you see the pollen record of
the last about 5,000 years.
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So you read the pollen diagram
always from the bottom to the top.
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And at the bottom of the record,
you see the forest composition,
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the black parts of the record.
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And that are certain families
that make up the forest.
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And then you see a moment that
the forest is decreasing rapidly, and
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the herbs are increasing also rapidly.
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So, people come in, they start to clear
the forest, and they build their villages.
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And they use all the surface for
their every cultural production.
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What did they produce?
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Well look at the records,
you see the record of maize and so
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they produced maize.
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And you see a record next to it called
chenopodioideae and that is quinoa.
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Maize and quinoa were the most
important staple foods of the Mayas.
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So you see a period of almost 2,000 years
of a lot of agricultural production.
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And then you see that
the production decreased, and
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you see that the open space in the Maya
lowlands became covered again by forest.
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What happened at the end
of the Maya culture?
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If we date this record
with radiocarbon dates,
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then we see that the change is
dated about 900 Anno Domini.
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Well what happened 900 Anno Domini?
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Probably this is the cause
of severe droughts.
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So the vegetation gives a good suggestion
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that climactic drought is the reason
of the end of the Maya civilization.
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Now we go to a deep sea core.
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And this record is a titanium record,
comes from the Cariaco trench
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located offshore Venezuela,
also in the Caribbean basin.
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And titanium is an terrestrial element and
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is transported to the ocean
under dry conditions.
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Here you see a record of
the last 2,000 years.
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And you see that several
changes in the titanium record
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show that climate conditions
are quite unstable.
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The yellow part is zoomed in and if you
go to the middle part of this figure and
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then you see a period of about 200 years,
150 years long.
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And you see that this period is the end
often longer period of increasing dryness.
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And if we zoom in this period,
then we go to the top part of this record,
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and then we see about
200 years of history.
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And this really a fascinating
part of the record,
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look at the colored bands in this figure.
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And there you see the dry periods.
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The first dry period has a duration
of about three to four years.
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And then every time with 40 year steps,
you see a dry period of 9 years.
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A dry period of 3 years, and 47 years
later, you see a dry period of 6 years.
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Well you can imagine that people that live
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in an area where drought
is really important.
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If you have every few decades a period
of many years of climatic drought.
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That the agricultural
production will crash, and
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that the populations
has a shortage of food.
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So we think that we see here good
arguments that climatic drought
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was the reason around 900 Anno Domini
that the Maya civilization
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was unable to continue with sufficient
food production and finally crashed.
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Well the conclusion of this
story is that sediments and peat
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are a perfect archive to learn the climate
and environmental conditions of the past.
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And we also see that
climate conditions had
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a significant impact on
the cultural history.
