Download 7th Grade Science Notes

6th Grade Science Notes
April 18, 2006
Alfred Wegener
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A German scientist named Alfred Wegener was studying ancient climates in 1910 when he
observed that many of the continents seemed to fit together like a puzzle.
Wegener formed an hypothesis that the continents had once been joined together in a giant
landmass he called “Pangea” meaning “all lands”. He also thought that they had drifted into
their present position so his theory became known as the “Continental Drift Theory”.
Wegener spent many years searching for evidence to support his theory and he published it in a
book in 1915 called “The Origin of Continents and Oceans”
Most scientists ignored or ridiculed Wegener’s theory because he could not prove how the
continents moved. At that time, the “apple theory” was popular which said that the earth was
cooling and shrinking so that the outer crust was wrinkling over the smaller core. Wegener
proposed that the continental plates plowed through the crust like ships. Neither theory was
considered a good explanation for the formation of landforms on the planet.
Alfred Wegener died during a research expedition in Greenland in 1930. His theory was finally
proven correct when a mechanism for continental drift was discovered in the 1960’s.
The evidence
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Landforms such as mountain ranges in North America and Europe, South Africa and Argentina,
and West Africa and Brazil are the same age, formed in the same way and contain the same
mineral deposits.
Fossils of plants such as Glossopteris and animals such as Mesosaurus were found on widely
separated continents: Africa, South America, India, Australia, and Antarctica. Did these
organisms develop independently, or did they somehow move across the ocean?
The ancient climate of many of the continents had changed drastically over the past 300 million
years. Glaciers once covered the warm lands of Africa, India , Australia and South America and
lands far to the north showed evidence of a tropical climate 300 million years ago. Did the Earth’s
climate change that radically or were the continents in different positions 300 million years ago?
Pangea
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The Theory of Continental Drift states that all the continents were once joined together in a single
landmass called Pangea. Pangea broke apart and the continents drifted slowly to their present
locations. They are still moving today.
Pangea existed about 300 mya.
About 200 mya Pangea began to break apart along the plate boundaries. It first formed two large
landmasses called Laurasia to the north and Gondwana to the south.
About 65 mya ( around the time dinosaurs became extinct) the continents broke up and began to
move to their present locations.