Do the continents have a Rubber Soul? Nope, the continents rest on plates made of a layer of the Earth's crust and its mantle, known collectively as the lithosphere. Plates are different sizes, with some plates more than 124 miles (200 km) thick [source: Kious]. Below the lithosphere is a fluid layer of rock called the asthenosphere. The plates are rigid slabs almost floating along in the asthenosphere, but scientists still aren't sure what causes the plates to move. They know it's somehow related to convection currents in the Earth's crust, in which hot materials rise upward as cooler materials flow downward, but they haven't figured out the precise relationship.
Scientists do know how the plates move, though.
- Two plates can move away from each other.
- Two plates can collide.
- One plate can be pushed under another plate.
- Plates can slide past each other sideways.
Now that we know a little bit about how plates move, we can turn again to supercontinents. The oldest supercontinent is known as Rodinia, and it formed about 1 billion years ago [source: Encyclopædia Britannica]. The evidence for all of the supercontinents is limited because the sea floor is always regenerating itself, so Pangaea, the youngest, has the most.
Before Pangaea became a supercontinent, it existed first as separate continents. Three large continental plates came together to form what's now the Northern Hemisphere, and that landmass merged with what is now the Southern Hemisphere. Pangaea existed during the late Paleozoic and Mesozoic eras, or about 200 to 300 million years ago [source: Oreskes].
Pangaea existed for approximately 100 million years before it began to divide into the seven continents we know and love today [source: Williams, Nield]. It first broke into two large landmasses: Laurasia, which was roughly the Northern Hemisphere, and Gondwanaland, which was the Southern Hemisphere. Laurasia split into North America and Eurasia, and Gondwanaland produced Africa, Antarctica, Australia and South America, with some of the pieces rotating slightly as they separated.
The plates continue to move, with the most action these days located at the East African Rift. Some geologists think that if they keep moving, the three plates that meet at the African coastline will separate, causing the Indian Ocean to flood the area and separating the Horn of Africa from the mainland [source: Kious].
How fast does all this happen? The magnetic striping around the places where the sea floor spreads provide a way to measure the continental movement, which, in some places, nears a rate of almost 4 inches (10 centimeters) per year [source: Skinner]. The Mid-Atlantic Ridge moves less than 1 inch (2.5 centimeters) a year, so over millions of years, the Atlantic Ocean has gone from being a tiny inlet to the size we know it today [source: Kious]. Scientists like to compare the speed at which continents move to the speed at which our fingernails grow [source: Reina].
Although the movements are slow, Africa is moving toward southern Europe, and Australia and Southeast Asia will collide [source: Encyclopædia Britannica]. These are the first movements toward another supercontinent. It'll take longer than a hard day's night, though; scientists predict the continents will reconnect in another 250 million years [source: Nield].
More Great Links
- Coney, Peter. "Plate Tectonics." Microsoft Encarta Online Encyclopedia. 2007. (May 2, 2008)http://encarta.msn.com/encyclopedia_761554623/Plate_Tectonics.html
- "Earth." The World Book Student Discovery Encyclopedia. 2005. (May 2, 2008)http://www.nasa.gov/worldbook/wbkids/k_earth.html
- Kious, W. Jacquelyne and Robert I. Tilling. "This Dynamic Earth: The Story of Plate Tectonics." U.S. Department of the Interior/U.S. Geological Survey. 1996.
- Nield, Ted. "Supercontinent: Ten Billion Years in the Life of Our Planet." Harvard University Press. 2007.
- Oreskes, Naomi, ed. "Plate Tectonics." Westview Press. 2001.
- "Pangea." Encyclopædia Britannica Online. 2008. (May 2, 2008)http://www.britannica.com/EBchecked/topic/441211/Pangea
- "Pangaea." Microsoft Encarta Online Encyclopedia. 2007. (May 2, 2008)http://encarta.msn.com/encyclopedia_761586400/Pangaea.html
- Reina, Mary. "Mapping Our Drifting Continents." Faces. November 2005.
- Skinner, Brian J. and Stephen C. Porter. "The Dynamic Earth: An Introduction to Physical Geology, Second Edition." John Wiley & Sons, Inc. 1992.
- Williams, Caroline and Ted Nield. "Pangaea, the comeback." NewScientist. Oct. 20, 2007. (May 6, 2008)http://www.science.org.au/nova/newscientist/104ns_011.htm