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Paleoclimatology: Pangaea
The distribution of
continents and oceans on
Earth’s surface has a
profound effect on climate.
Today the continents are
spread around the globe,
with oceans in between.
Earth’s climate ranges
from hot along the equator
to cold at the poles. Some
places on the continents
are very dry, while others
are wet. In some places
weather changes
throughout the year with
the seasons. In others,
weather stays about the
same all year long.
But Earth’s climate has not
always been like it is today.
It has gone through periods
of higher average global
temperatures, as well as
periods of much lower
temperatures. Areas that
are now freezing, such as
Antarctica, were once
warm. Areas that are now
dry, such as the Sahara
Desert in Northern Africa,
were once crisscrossed
with lakes and rivers. Why
do climates on Earth
Many factors affect climates on Earth. The top map shows major and minor global
change so dramatically
climate zones today; the bottom map shows major climate zones approximately 230
million years ago, when all of Earth’s land formed a supercontinent called Pangaea,
over time? A primary
and ocean currents could travel uninterrupted from pole to pole.
reason is that the locations
of the continents and
oceans, and the topography of the continents themselves, also change. What evidence do scientists
have for these changes? To find the answer, let’s take a look at what Earth was like several hundred
million years ago.
As described by the theory of plate tectonics, oceans are continuously opening and closing. Continents
“drift” from one part of the globe to another. Many times throughout geologic history, Earth’s land
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Paleoclimatology: Pangaea
masses have come together to form supercontinents and have broken apart to form individual
continents. Between about 300 and 200 million years ago, all of Earth’s continents were combined
into one giant supercontinent known as Pangaea. (Pangaea comes from the Greek words pan,
meaning “all,” and gaia, meaning “Earth.”)
Paleoclimatologists, scientists who study ancient climates, study rocks that formed at that time and
fossils of living things that were alive at that time to understand what life was like on this
supercontinent. Fossilized mammals and reptiles that lived on Pangaea have been found around the
globe. The diversity of fossils suggests that Pangaea had a variety of coastal regions and inland areas.
Its land mass extended nearly from the South Pole to the North Pole. Large mountain ranges spanned
the coasts, the results of collisions between tectonic plates.
Many of Pangaea’s large inland areas were very
dry. Scientists have found evidence for this arid
climate in the rocks of the Triassic and Jurassic
periods. Many thick layers of evaporite rocks,
such as halite, formed during these periods.
Evaporite rocks are formed in arid climates as
rain in the mountains brings mineral-rich water
down into the basins. When the water
evaporates, the minerals are left behind, forming
great, salty deposits such as those seen today in
Death Valley, California.
As Pangaea began to break up into the smaller
continents Gondwana and Laurentia during the
Jurassic and Cretaceous periods, climates around
Much of inland Pangaea had an arid climate. Flat,
the globe began to change. Why does the
former lake beds—such as this region in Death Valley—
distribution of continents and oceans on Earth’s
would have been ideal places for evaporite minerals to
surface matter? The placement of continents
form. According to the principle of uniformitarianism, the
same processes that shape Death Valley today would
affects the movement of ocean currents. Ocean
have shaped Pangaea millions of years ago.
currents help to distribute heat from solar
radiation throughout the planet, from the
equator to the poles. When all the continents were joined together as Pangaea, heat was distributed
more evenly, and climate differences between latitudes were less extreme. Water was not cold enough
at the north pole for an ice cap to form there, though evidence does suggest that a continental ice cap
existed over the South Pole. Today, the scattered positions of the continents interrupts and deflects
the paths of ocean currents. Each ocean has different currents, and less heat from the equator reaches
the frigid poles.
Air temperatures are another crucial element of climate. As solar energy is absorbed by the land or
water, some of it is re-radiated into the air. It is this re-radiated energy that determines air
tempertures near Earth’s surface. Water has a much higher specific heat than land. In other words, if
equal areas of land and water are exposed to the same intensities of sunlight, for the same lengths of
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Paleoclimatology: Pangaea
time, the land would reach a higher temperature. Thus, during the day, the air over land will generally
heat up faster and reach higher temperatures than the air over water. When the Sun goes down,
however, the land will lose its heat more quickly than the water. Therefore, at night the air over land is
usually cooler than the air over water. For the same reasons, coastal areas are usually cooler in the
summer and warmer in the winter than inland areas at the same latitude. Comparing the maps on the
first page of this passage, one sees large deserts in the interiors of both Pangaea and the modern
continents.
These are only a few examples of how the positions of the continents can have a significant
effect on Earth’s climate. Understanding how the distribution of land and water has affected
the climate in the past can help us understand the factors that are controlling global climate
today.
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