Introduction to Plate Tectonics Alfred Wegener & Continental Drift

QOD How do scientific theories develop?

What is a Theory? Fundamental paradigm Synthesizes a body of evidence Testable statement about how nature operates. Can be replicated Can take years and decades to be accepted THEORIES EXPLAIN SCIENTIFIC LAWS

What is a Scientific Law? Mathematical statement F=ma E=mc2 Empirical data Confined to a set of conditions E=mc2 , where c is the speed of light in a vacuum

Well-established laws and theories must ... be internally consistent and compatible with the best available evidence be successfully tested against a wide range of applicable phenomena and evidence possess appropriately broad and demonstrable effectiveness in further research.

Plate Tectonics Not “just a theory” Extensive data sets gathered over decades Evolutionary & Revolutionary!

Early Thoughts on the Motion of Continents 1596 -- Abraham Ortelius a Dutch map-maker in Thesaurus Geographicus. the Americas were "torn away from Europe and Africa . . . by earthquakes and floods" "The vestiges of the rupture reveal themselves, if someone brings forward a map of the world and considers carefully the coasts of the three [continents].“

1858-- Antonio Snider-Pellegrini Geographer Maps show his version of how the American and African continents may once have fit together, then later separated. Left: The formerly joined continents before their separation. Right: The continents after the separation. (Reproductions of the original maps courtesy of University of California, Berkeley.)

Continental Drift 1912 – the full-blown scientific theory of Continental Drift Alfred Lothar Wegener -- a 32-year-old German meteorologist Studied evidence from all the Earth Sciences Proposed the supercontinent Pangaea Supporter: Alexander Du Toit, Professor of Geology at Johannesburg University Named Laurasia and Gondwanaland

Activity Finish analyzing the evidence that Alfred Wegener compiled

Pangaea -- a supercontinent began to split up 200 million years ago. Pangaea first broke into two large continental landmasses 1) Laurasia in the northern hemisphere 2) Gondwanaland in the southern hemisphere. Laurasia and Gondwanaland continued to break apart into the various smaller continents that exist today.

Wegener's Evidence fit of the South American and African continents unusual geologic structures on both continents plant and animal fossils found on the matching coastlines of South America and Africa. it was physically impossible for most of these organisms to have swum or have been transported across the vast oceans. the presence of identical fossil species along the coastal parts of Africa and South America was the most compelling evidence that the two continents were once joined.

A Explanation for many Observations The break-up of Pangaea also explained the evidence of dramatic climate changes on some continents. fossils of tropical plants in coal deposits in Antarctica distinctive fossil ferns (Glossopteris) discovered in now-polar regions glacial deposits in present-day arid Africa, such as the Vaal River valley of South Africa.

Convincing Others The scientific community firmly believed the continents and oceans to be permanent features on the Earth's surface. Wegener’s proposal was not well received

The Fatal Weakness There was no explanation for the kind of forces that would be strong enough to move such large masses of solid rock over such great distances. Wegener -- continents plowed through the ocean floor Harold Jeffreys, a noted English geophysicist, disagreed: it was physically impossible for a large mass of solid rock to plow through the ocean floor without breaking up.

Wegener’s Death He devoted the rest of his life to find additional evidence to defend his theory. He froze to death in 1930 during an expedition crossing the Greenland ice cap After his death, new evidence from ocean floor exploration and other studies rekindled interest in Wegener's theory, ultimately leading to the development of the theory of plate tectonics.