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CONTINENTAL DRIFT es/outreach/sumatra/pangaea.mov

The Theory of Continental Drift

Continental Drift First evidence: The jigsaw fit of the outline of the continental margins. Frances Bacon (1620): while reviewing the first maps of the coastlines of Africa and South America noted that the outlines of the continents appear as if they could fit together.

This “jigsaw” fit of continental margins is best when the outline is the edges of the continental shelves.

Frances Placet (1668) was the first to suggest that the continents were actually fixed together as suggested by their outlines. Suggested that the continents had been torn apart by the biblical flood.

Alfred L. Wegener  Geologist Alfred Wegener noticed similar rocks & fossil remains were found on continents which seemed to fit together  He called this “super” continent Pangaea  In 1912 Wegener published the first version & died defending his theory  Geologist Alfred Wegener noticed similar rocks & fossil remains were found on continents which seemed to fit together  He called this “super” continent Pangaea  In 1912 Wegener published the first version & died defending his theory

PANGAEA the large landmass that included all of Earth’s present day continents

Support for Continental Drift 1. SHAPE OF THE CONTINENTS Continents fit together like puzzle pieces 1. SHAPE OF THE CONTINENTS Continents fit together like puzzle pieces

Support for Continental Drift  Wegener was not the only one to notice the fit of the continents.  1858: Antonio Pelligrini depicted Africa and South America connected.  He was one of the first scientists to publish maps depicting the apparent fit of the continents.  Wegener was not the only one to notice the fit of the continents.  1858: Antonio Pelligrini depicted Africa and South America connected.  He was one of the first scientists to publish maps depicting the apparent fit of the continents. 1. SHAPE OF THE CONTINENTS

Mesosaurus was incapable of swimming across a large ocean. Seeds of glosopteris could not have been blown in by the wind or carried on ocean currents. 2. FOSSIL EVIDENCE SAME FOSSILS: DIFFERENT CONTINENTS Support for Continental Drift

3. ROCK EVIDENCE – Mountain ranges Support for Continental Drift  SAME ROCK: DIFFERENT RANGE Existing mountain ranges separated by vast oceans contain rocks of identical mineral content.  A prime example are the Appalachian Mountains in the eastern U.S and the Caledonian Mountains in the British Isles.  SAME ROCK: DIFFERENT RANGE Existing mountain ranges separated by vast oceans contain rocks of identical mineral content.  A prime example are the Appalachian Mountains in the eastern U.S and the Caledonian Mountains in the British Isles.

Sequence of Rocks  Same rock patterns found in South America, India, Africa, Antarctica and Australia

SAME SCARS: DIFFERENT CONTINENTS Support for Continental Drift 4. GLACIAL SCARS

5. LOCATION OF COAL DEPOSITS Coal deposits have been found in temperate and polar regions; however, coal is formed in tropical regions. Support for Continental Drift

Paleoclimate evidence In the modern world glaciers are found near the north and south poles. Deserts are largely found in bands that are parallel to the equator. Extensive reef complexes lie along the equator.

Desert deposits and reefs that are several hundred million years old are found in bands that suggest the equator was oriented as shown on the left. If we assume that the poles and equator are fixed, the continents must have been in different positions as shown on the left.

Ancient “cratons” within continents match up when they are brought together like a jigsaw puzzle. A Craton is an old and stable part of the Continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates.

CONTINENTAL DRIFT IN DOUBT Why didn’t people believe in continental drift?  People couldn’t image how the earth could be millions of years old  People couldn’t image a force great enough to move the continents BUT by the 1960’s evidence would prove continental drift is TRUE and…. The story continues (as does all good science!) Why didn’t people believe in continental drift?  People couldn’t image how the earth could be millions of years old  People couldn’t image a force great enough to move the continents BUT by the 1960’s evidence would prove continental drift is TRUE and…. The story continues (as does all good science!)