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In Review?
 Pangaea - was a supercontinent that existed
about 300 million years ago.
 About 180 million years ago Pangaea began
to break up.
 Through various land mass changes,
Pangaea split along faults in the earth into
two “super continents” and eventually some
smaller land masses.
 These two different continents developed
into two completely different ecosystems.
 An ecosystem is a community of plants, animals
and smaller organisms that live, feed, reproduce
and interact in the same area or environment.
 Some ecosystems are very large.
 On the other hand, some ecosystems may be
physically small, such as you would find in a
meadow at the edge of a forest.
 While various forms of life may be found in both
areas, the species that live in the forest ecosystem
are usually very different from those that inhabit
the meadow, even though the two environments
are right next to each other.
The Movement of People
 In turn we came to the conclusion that at some
point in human history, people existed and began
to spread out.
 Over time human populations migrated in all
directions throughout Africa, Europe and Asia
 How and when did humans come to the
 As original inhabitants of North America as far
back as Pangaea.
 Or people traveled over the Siberian Land Bridge
known as Beringia
Humans evolved differently
Small pox
Measles, TB
Flu, Pertussis
Ecological collision
 Now the stage is set for an ecological collision
between these two completely different ecosystems.
 As we reviewed, people from Africa, Asia and
Europe had visited the Americas prior to Columbus.
 However, with Columbus comes the great ecological
watershed the world has ever seen.
 Some people have compared this catastrophic event just as
significant as the disappearance of the dinosaurs.
 With the arrival of Columbus in the Americas, the animal,
plant, and bacterial life of these two worlds began to mix.
 By reuniting formerly biologically distinct land masses, the
Columbian Exchange had dramatic and lasting effects on
the world.
The Columbian exchange
 Pangea as been resurrected and has reemerged.
 No longer do two ecosystems exist.
 The European ecosystem has invaded the North
American Ecosystem.
 This process, first studied comprehensively by
American historian Alfred Crosby, was called the
Columbian Exchange.
 The Columbian Exchange is the
movement of plants, animals, and
diseases between the Eastern and
Western hemispheres.
Ecological imperialism
 Invasive species brought over
by Columbus and eventually
other European Explores took
over the North American
 While the apparent and
intentional transfer of
domestic animals and home
grown plants were obvious.
 It was the unseen bugs,
insects and bacteria which
caused most harm.
 The Columbian Exchange brought horses, cattle, sheep, goats,
pigs to the Americas.
 Within 100 years after Columbus, huge herds of wild cattle
roamed many of the natural grasslands of the Americas. Wild
cattle menaced the food crops of Native Americans.
 Before Columbus, North American had no large animals and none
of the other animals present in the Americas were suitable for
 In contrast, Eurasia had 72 large animal species, of which 13
were suitable for domestication. So, while American had plenty of
good food crops available before 1492, they had few domesticated
 Native Americans first encountered the horse as a fearsome war
beast ridden by Spanish conquistadors. However, they soon
learned to ride and raise horses themselves.
 Before Columbus, the Americas had plenty of
domesticated plants. By the time Columbus had
arrived, dozens of plants were in regular use, the most
important of which were maize (corn), potatoes,
cassava, and various beans and squashes. Lesser crops
included sweet potato, papaya, pineapple, tomato,
avocado, guava, peanuts, chili peppers, and cacao, the
raw form of cocoa.
 Within 20 years of Columbus’ last voyage, maize
had established itself in Europe and North Africa.
 Despite maize’s success, the potato had a stronger
impact in improving the food supply and in
promoting population growth in Europe and Asia.
 . In turn the population explosion laid the foundation
for other developments such as the Industrial
Revolution and modern European imperialism. The
potato has fed many populations around the world
 By far the most dramatic and devastating impact of the
Columbian Exchange was the introduction of new diseases into
the Americas.
 When the first inhabitants of the Americas arrived across the
Bering land bridge, they brought few diseases with them.
 Soon after 1492, Europeans inadvertently introduced these
diseases to the Americas.
 People who lived in Europe had developed immunities to these
diseases because they had long existed among most populations.
 However, the Native Americans had no such immunities, which
produced catastrophic deaths throughout the Americas.
 In all, between 1492 and 1650, perhaps 90 percent of the first
Americans had died.
 This loss is considered among the largest demographic disasters
in human history.
The Impact
 All this had nothing to do with superiority or inferiority of
ecosystems in any sense. It has to do with environmental
 Native Americans were accustomed to living in one particular
kind of environment, Europeans and Africans in another.
 When the Europeans came to America, they brought with them
all their plants, animals, and bacteria, creating a kind of
environment to which they were already adapted, and so they
increased in number.
 Native Americans had not adapted to European bacteria, and so
their population numbers plunged.
 In turn the Europeans believed they were ordained by God to
inherit the land.