Pangea
Hypothetical protocontinent proposed by Alfred Wegener in 1912 as part of his theory of continental drift.
Pangea (from Greek: pangaia, “all earth”) supposedly covered about half the Earth and was completely surrounded by a world ocean called Panthalassa.
Early in the Jurassic Period (approximately 200 million to 146 million years ago), Pangea began to break apart. Its segments, Laurasia (composed of all the present-day northern continents) and Gondwana (the present-day southern continents) gradually receded, resulting in the formation of the Atlantic and Indian oceans.
Gondwana
Hypothetical former supercontinent in the Southern Hemisphere, which included modern South America, Africa, southern Europe, India, Australia, and much of the Middle East and Antarctica.
The concept that the continents were at one time joined was first set forth in detail by Alfred Wegener in 1912.
He envisioned a single great landmass, Pangea, which supposedly began to separate early in the Jurassic Period (approximately 200 million to 146 million years ago). Subsequent workers distinguished between a southern landmass, Gondwana, and Laurasia to the north. See also continental drift.
born Nov. 1, 1880, Berlin, Ger.
died Nov. 1930, Greenland
died Nov. 1930, Greenland
German meteorologist and geophysicist.
After earning a Ph.D. in astronomy (1905), he became interested in paleoclimatology and traveled to Greenland to research polar air circulation.
He formulated the first complete statement of the continental drift hypothesis, which he presented in The Origin of Continents and Oceans (1915). His theory won some adherents, but by 1930 most geologists had rejected it because of the implausibility of his postulations for the driving force behind the continents' movement. It was resurrected in the 1960s as part of the theory of plate tectonics. Wegener died during his fourth expedition to Greenland.
Plate Tectonics
The theory revolutionized the geological sciences in the 1960s by combining the earlier idea of continental drift and the new concept of seafloor spreading into a coherent whole.
Each plate consists of rigid rock created by upwelling magma at oceanic ridges, where plates diverge.
Where two plates converge, a subduction zone forms, in which one plate is forced under another and into the Earth's mantle.
The majority of the earthquakes and volcanoes on the Earth's surface occur along the margins of tectonic plates. The interior of a plate moves as a rigid body, with only minor flexing, few earthquakes, and relatively little volcanic activity.
Continential Drift
Large-scale movements of continents over the course of geologic time.
Art:The theory of continental drift is based on the concept that the continental and oceanic crusts are …
* The theory of continental drift is based on the concept that the continental and oceanic crusts are …
The first complete theory of continental drift was proposed in 1912 by Alfred Wegener, who postulated that a single supercontinent, which he called Pangea, fragmented late in the Triassic Period (approximately 250–200 million years ago) and that the parts began to move away from one another. He pointed to the similarity of rock strata in the Americas and Africa as evidence to support his hypothesis. Wegener's ideas received support from the concepts of seafloor spreading and plate tectonics beginning in the 1960s. The modern theory states that the Americas were joined with Europe and Africa until c. 190 million years ago, when they split apart along what is now the Mid-Atlantic Ridge. Subsequent tectonic plate movements took the continents to their present positions.
Seafloor Spreading
Theory that oceanic crust forms along submarine mountain zones, known collectively as the oceanic ridge system, and spreads out laterally away from them.
This idea, proposed by U.S. geophysicist Harry H. Hess (1906–1969) in 1960, was pivotal in the development of the theory of plate tectonics.
