You cannot download interactives. These tectonic plates rest upon the convecting mantle, which causes them to move. The movements of these plates can account for noticeable geologic events such as earthquakes, volcanic eruptions, and more subtle yet sublime events, like the building of mountains.
Teach your students about plate tectonics using these classroom resources. Continental drift describes one of the earliest ways geologists thought continents moved over time. Today, the theory of continental drift has been replaced by the science of plate tectonics.
The theory of plate tectonics revolutionized the earth sciences by explaining how the movement of geologic plates causes mountain building, volcanoes, and earthquakes. In , after decades of tediously collecting and mapping ocean sonar data, scientists began to see a fairly accurate picture of the seafloor emerge. The Tharp-Heezen map illustrated the geological features that characterize the seafloor and became a crucial factor in the acceptance of the theories of plate tectonics and continental drift.
Today, these theories serve as the foundation upon which we understand the geologic processes that shape the Earth. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image Alfred Wegener in Greenland Plate tectonics is the theory that Earth's land masses are in constant motion.
Photograph from Pictoral Press. Twitter Facebook Pinterest Google Classroom. Article Vocabulary. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
Media If a media asset is downloadable, a download button appears in the corner of the media viewer. Text Text on this page is printable and can be used according to our Terms of Service. Interactives Any interactives on this page can only be played while you are visiting our website. Related Resources. Wegener said little. He just sat smoking his pipe and listening.
His attitude seems to have mirrored that of Galileo who, forced to recant Copernicus' theory that the Earth moves around the sun, is said to have murmured, "Nevertheless, it moves! His major problem was finding a force or forces that could make the continents "plow around in the mantle," as one critic put it. Wegener tentatively suggested two candidates: centrifugal force caused by the rotation of the Earth, and tidal-type waves in the Earth itself generated by the gravitational pull of the sun and moon.
He realized these forces were inadequate. Continental drift, faults and compressions, earthquakes, volcanicity, [ocean] transgression cycles and [apparent] polar wandering are undoubtedly connected on a grand scale.
Wegener's final revison cited supporting evidence from many fields, including testimonials from scientists who found his hypothesis resolved difficulties in their disciplines much better than the old theories.
Climatology was one such discipline. Fossils and geologic evidence show that most of the continents used to have startlingly different climates than they do today. This theory is called catastrophism, according to the USGS. Plate tectonics is now the widely accepted theory that Earth's crust is fractured into rigid, moving plates.
In the s, scientists discovered the plate edges through magnetic surveys of the ocean floor and through the seismic listening networks built to monitor nuclear testing, according to Encyclopedia Britannica.
Alternating patterns of magnetic anomalies on the ocean floor indicated seafloor spreading , where new plate material is born. Magnetic minerals aligned in ancient rocks on continents also showed that the continents have shifted relative to one another. A map of the continents inspired Wegener's quest to explain Earth's geologic history. Trained as a meteorologist, he was intrigued by the interlocking fit of Africa's and South America's shorelines.
Wegener then assembled an impressive amount of evidence to show that Earth's continents were once connected in a single supercontinent. Wegener knew that fossil plants and animals such as mesosaurs , a freshwater reptile found only South America and Africa during the Permian period, could be found on many continents. He also matched up rocks on either side of the Atlantic Ocean like puzzle pieces.
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