Stay up to date with Current Events from WebLessons, updated every Monday morning. Click Here to view the archive of past articles.
As a kid you learned that Earth has continents. American students are taught there are seven continents: Africa, Antarctica, Asia, Australia, Europe, North America, and South America. Students in other countries are taught there are five or six continents. (Which do you think they consider one continent?) One thing we can agree upon: long, long ago, there was but one supercontinent called Pangaea. About 200 million years ago, Pangaea broke into two supercontinents: Laurasia and Gondwana. Later, about 165 million years ago, Laurasia and Gondwana gave way to new continents, the ones we know today. But, scientists have not always agreed on the Gondwana-era position of these new continents.
Knowing how Earth changed millions of years ago is tricky. Millions of years ago, there were no satellite images, video recordings, or newspaper articles recording Earth’s development. Yet, it is important. It may seem as if the continents are separate, fixed land masses with little to do with each other. This is not the case. Continents are constantly changing, we just do not notice it. It is kind of like watching a child grow--you do not notice how much a child grows from day to day, but in a year the mark on the wall that records her height will be higher.
So how do we identify where continents’ were millions of years ago? Sometimes, the borders of continents fit together like pieces in a jigsaw puzzle and easily reveal how they once connected. This can be seen in the coastlines of eastern South America and western Africa. Other times scientists must gather evidence from Earth’s geology. Mountain ranges, mineral deposits, and oil reservoirs help point the way.
Researchers from England and Australia have been gathering geological clues to solve a long-standing debate about the locations of Australia, Antarctica, and India 165 million years ago. Their findings, which have just been published, remind us that understanding continental drift and the history of Earth helps us understand the Earth we live on today.
How Earth Works—
The continents are continually moving--shifting, drifting, sliding. “Why? How?’’ you might ask. The answer lies in plates under the surface of Earth. Plate tectonics explains how the Earth works. The National Oceanic and Atmospheric Administration (NOAA) interactive explains why plate tectonics are fundamental (watch the tab titled Global Impact) and introduces you to the structure of Earth (play the Lesson tab.)
Annenberg Learner’s interactive exhibit, Dynamic Earth, dissects Earth’s structure. Earth’s outermost layer, the lithosphere, is made up of movable plates. Tectonic plates cover Earth’s surface; every landmass and ocean has a tectonic plate under it. The number, size, and motion of the plates changes over time. Right now, there are eight large plates and eight smaller ones. View a map of the plates. Scroll down to read about the three types of plate boundaries, and to see a map of where in the world each type of plate exists. Test your newfound knowledge with a two-part Plates and Boundaries challenge. Return to NOAA for two more challenges: Can you correctly place each plate on a map? Can you locate the plate boundary?
The interaction of these plates slowly transforms the surface of Earth. Collision points create mineral seams. Divergent boundaries often develop oil reservoirs. Transform boundaries slide past each other, often triggering earthquakes. See how the movement of the plates affects Earth’s geography and natural disasters in the section titled, Slip, Slide, and Collide. Then face the Plate Interactions challenge.
A New Theory—
Sometimes, commonly held scientific beliefs turn out to be incorrect. Cases in point: the Earth is flat, the Sun revolves around the Earth. Like Copernicus, who was mocked for proposing that the Sun is at the center of the solar system, Alfred Wegener faced skepticism when he first proposed his theory of continental drift. Visit the Smithsonian Museum’s interactive exhibit, The Dynamic Earth. Open the tab titled Plate Tectonics, and then click on the chapter titled Geological Revolution. Explore Wegener’s theory, Harry Hess’ discovery, and the evidence for continental drift. Use the menu pop-up in the bottom left corner to see all the exhibits in this section.
Billions of Years Ago—
Plate tectonics helps scientists understand how and where earthquakes and volcanoes form, and how the continents came to be in their current formation. However, it also reveals how the continents formed. Return to the Plate Tectonics tab at the Smithsonian Museum site. This time select the Ancient Continents section. Explore the three exhibits in this section to discover how continents were born, how the surface of Earth has changed over the eons, and how these changes affect our natural resources.
A Slow Motion Ballet—
Earth is a dynamic system. Key to its continual transformation are the plates that drift slowly upon the lithosphere, sliding, separating, and spreading. Plate tectonics is key to the Earth as a whole system. For a final view of how important their movement is, visit the Orientation Theater (found in the Plate Tectonics tab) and watch the movie, The World’s Most Magnificent Show. Then revisit Annenberg Learner’s site for a final challenge about our Dynamic Earth.