4 minute read

Continental Drift

Pangaea Splits

During the formation of Pangaea, the collision of North America and northwestern Africa uplifted a mountain range 621 mi (1,000 km) long and as tall as the Himalayas, the much-eroded roots of which can still be traced from Louisiana to Scandinavia. The Appalachians are remnants of these mountains, the tallest of which centered over today's Atlantic Coastal Plain and over the North American continental shelf. Pangaea's crushing closure shortened the eastern margin of North America by at least 161 mi (260 km).

The internal crunching continued after the formation of Pangaea, but most of the colliding shifted from the east coast of North America to the western edge of the continent. Pangaea drifted northward before it began to break up, and it plowed into the Panthalassa ocean floor The Pangaea supercontinent (top) and its break-up into Laurasia and Gondwanaland (bottom). Contemporary continental outlines are shown in gray. Illustration by Hans & Cassidy. Courtesy of Gale Group. and created some of today's western mountains. The rifting of Pangaea that began 200 million years ago (the end of the Triassic period) forced up most of the mountain ranges from Alaska to southern Chile as North and South America ground west into and over more ocean floor.

The tearing apart of Pangaea produced long valleys that ran roughly parallel to the east coasts of the Americas and the west coasts of Europe and Africa. The floors of these valleys dropped down tremendously in elevation. One of the valleys filled with seawater and became the Atlantic Ocean, which still grows larger every year. Other valleys gradually choked with sediment eroded off the ridges on either side. Today, many of these former low spots lie buried beneath thousands of feet of debris. The formation of the valleys did not occur along the same line as the collision 100 million years before; a chunk of Gondwana now sits below the eastern United States.

Pangaea began to break up around 200 million years ago with the separation of Laurasia from Gondwana, and the continents we know began to take shape in the late Jurassic about 152 million years ago. New oceans began to open up 94 million years ago (the Cretaceous period). India also began to separate from Antarctica, and Australia moved away from the still united South America and Africa. The Atlantic zippered open northward for the next few tens of millions of years until Greenland eventually tore from northern Europe. By about 65 million years ago, all the present continents and oceans had formed and were sliding toward their current locations while India drifted north to smack the south side of Asia.

Current Pangaea research no longer focuses on whether or not it existed, but refines the matching of the continental margins. Studies also center on parts of Earth's crust that are most active to understand both past and future movements along plate boundaries (including earthquakes and volcanic activity) and continuing Continental Drift. For example, the East African Rift Valley is a plate boundary that is opening like a pair of scissors, and, between Africa and Antarctica, new ocean floor is being created, so the two African plates are shifting further from Antarctica. Eventually, 250 to 300 million years in the future, experts theorize that Pangaea will unite all the continents again. In another aspect of the study of Continental Drift, scientists are also trying to better understand the relatively sudden continental shift that occurred 500 million years ago that led to the formation of Pangaea. The distribution of the land mass over the spinning globe may have caused continents to relocate comparatively rapidly and may also have stimulated extraordinary evolutionary changes that produced new and diverse forms of life in the Cambrian period, also about 500 million years ago.

Resources

Books

Hancock, P.L. and B.J. Skinner, eds. The Oxford Companion to the Earth. New York: Oxford University Press, 2000.

Tarbuck, Edward. D., Frederick K. Lutgens, and Tasa Dennis. Earth: An Introduction to Physical Geology. 7th ed. Upper Saddle River, NJ: Prentice Hall, 2002.

Winchester, Simon. The Map That Changed the World: William Smith and the Birth of Modern Geology. New York: Harper Collins, 2001.


Periodicals

Buffett, Bruce A., "Earth's Core and the Geodynamo." Science (June 16, 2000): 2007–2012.

Hellfrich, George, and Wood, Bernard. "The Earth's Mantle." Nature (August 2, 2001): 501–507.


Other

United States Department of the Interior, U.S.Geological Survey. "This Dynamic Earth: The Story of Plate Tectonics." February 21, 2002 (cited February 5, 2003). <http://pubs. usgs.gov/publications/text/dynamic.html>.


Ed Fox

K. Lee Lerner

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Continental Drift theory

—Alfred Wegener's theory that all the continents once formed a giant continent called Pangaea and later shifted to their present positions.

Gondwana (Gondwanaland)

—The southern half of Pangaea that included today's South America, Africa, India, Australia, and Antarctica.

Laurasia

—The northern half of Pangaea that included today's North America, Greenland, Europe, and Asia.

Pangaea (Pangea)

—The supercontinent from approximately 200–300 million years ago, which was composed of all today's landmasses.

Panthalassa

—The ocean covering the opposite site of the globe from Pangaea. Panthalassa means "All Ocean."

Wegener, Alfred

—German meteorologist (1880–1930), developer of the Continental Drift theory.

Additional topics

Science EncyclopediaScience & Philosophy: Condensation to CoshContinental Drift - History Of Wegener's Theory, Evidence Of The Theory, Formation Of Pangaea, Pangaea Splits