Continental drift
Overview
 
Continental drift is the movement of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius
Abraham Ortelius
thumb|250px|Abraham Ortelius by [[Peter Paul Rubens]]Abraham Ortelius thumb|250px|Abraham Ortelius by [[Peter Paul Rubens]]Abraham Ortelius (Abraham Ortels) thumb|250px|Abraham Ortelius by [[Peter Paul Rubens]]Abraham Ortelius (Abraham Ortels) (April 14, 1527 – June 28,exile in England to take...

 in 1596 and was fully developed by Alfred Wegener
Alfred Wegener
Alfred Lothar Wegener was a German scientist, geophysicist, and meteorologist.He is most notable for his theory of continental drift , proposed in 1912, which hypothesized that the continents were slowly drifting around the Earth...

 in 1912. However, it was not until the development of the theory of plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

 in the 1960s, that a sufficient geological
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

 explanation of that movement was found.
Abraham Ortelius
Abraham Ortelius
thumb|250px|Abraham Ortelius by [[Peter Paul Rubens]]Abraham Ortelius thumb|250px|Abraham Ortelius by [[Peter Paul Rubens]]Abraham Ortelius (Abraham Ortels) thumb|250px|Abraham Ortelius by [[Peter Paul Rubens]]Abraham Ortelius (Abraham Ortels) (April 14, 1527 – June 28,exile in England to take...

  , Theodor Christoph Lilienthal (1756), Alexander von Humboldt
Alexander von Humboldt
Friedrich Wilhelm Heinrich Alexander Freiherr von Humboldt was a German naturalist and explorer, and the younger brother of the Prussian minister, philosopher and linguist Wilhelm von Humboldt...

 (1801 and 1845), Antonio Snider-Pellegrini
Antonio Snider-Pellegrini
Antonio Snider-Pellegrini was a French geographer and scientist who theorized about the possibility of continental drift, anticipating Wegener's theories concerning Pangaea by several decades....

 , and others had noted earlier that the shapes of continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...

s on opposite sides of the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

 (most notably, Africa and South America) seem to fit together.
Encyclopedia
Continental drift is the movement of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius
Abraham Ortelius
thumb|250px|Abraham Ortelius by [[Peter Paul Rubens]]Abraham Ortelius thumb|250px|Abraham Ortelius by [[Peter Paul Rubens]]Abraham Ortelius (Abraham Ortels) thumb|250px|Abraham Ortelius by [[Peter Paul Rubens]]Abraham Ortelius (Abraham Ortels) (April 14, 1527 – June 28,exile in England to take...

 in 1596 and was fully developed by Alfred Wegener
Alfred Wegener
Alfred Lothar Wegener was a German scientist, geophysicist, and meteorologist.He is most notable for his theory of continental drift , proposed in 1912, which hypothesized that the continents were slowly drifting around the Earth...

 in 1912. However, it was not until the development of the theory of plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

 in the 1960s, that a sufficient geological
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

 explanation of that movement was found.

Early history

Abraham Ortelius
Abraham Ortelius
thumb|250px|Abraham Ortelius by [[Peter Paul Rubens]]Abraham Ortelius thumb|250px|Abraham Ortelius by [[Peter Paul Rubens]]Abraham Ortelius (Abraham Ortels) thumb|250px|Abraham Ortelius by [[Peter Paul Rubens]]Abraham Ortelius (Abraham Ortels) (April 14, 1527 – June 28,exile in England to take...

  , Theodor Christoph Lilienthal (1756), Alexander von Humboldt
Alexander von Humboldt
Friedrich Wilhelm Heinrich Alexander Freiherr von Humboldt was a German naturalist and explorer, and the younger brother of the Prussian minister, philosopher and linguist Wilhelm von Humboldt...

 (1801 and 1845), Antonio Snider-Pellegrini
Antonio Snider-Pellegrini
Antonio Snider-Pellegrini was a French geographer and scientist who theorized about the possibility of continental drift, anticipating Wegener's theories concerning Pangaea by several decades....

 , and others had noted earlier that the shapes of continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...

s on opposite sides of the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

 (most notably, Africa and South America) seem to fit together. W. J. Kious described Ortelius' thoughts in this way:

Wegener and his predecessors

The hypothesis that the continents had once formed a single landmass before breaking apart and drifting to their present locations was fully formulated by Alfred Wegener
Alfred Wegener
Alfred Lothar Wegener was a German scientist, geophysicist, and meteorologist.He is most notable for his theory of continental drift , proposed in 1912, which hypothesized that the continents were slowly drifting around the Earth...

 in 1912.
Although Wegener's theory was formed independently and was more complete than those of his predecessors, Wegener later credited a number of past authors with similar ideas:
Franklin Coxworthy (between 1848 and 1890),
Roberto Mantovani
Roberto Mantovani
Roberto Mantovani , was an Italian geologist and violinist.Mantovani was born in Parma. His father, Timoteo, died seven months after his birth. His mother, Luigia Ferrari, directed him to studies, and at the age of 11 he was accepted as a boarder in the Royal School of Music, where he was...

 (between 1889 and 1909), William Henry Pickering
William Henry Pickering
William Henry Pickering was an American astronomer, brother of Edward Charles Pickering. He was elected a Fellow of the American Academy of Arts and Sciences in 1883.-Work:...

 (1907)
and Frank Bursley Taylor
Frank Bursley Taylor
Frank Bursley Taylor was an American geologist, the son of a lawyer in Fort Wayne, Indiana. He was a Harvard dropout who studied privately financed in large part by his wealthy father...

 (1908). John Perry
John Perry (engineer)
John Perry was a pioneering engineer and mathematician from Ireland. He was born on February 14, 1850 at Garvagh, County Londonderry, the second son of Samuel Perry and a Scottish-born wife....

 had written an 1895 paper proposing that the earth's interior was fluid, and disagreeing with Lord Kelvin on the age of the earth.

For example: the similarity of southern continent geological formations had led Roberto Mantovani
Roberto Mantovani
Roberto Mantovani , was an Italian geologist and violinist.Mantovani was born in Parma. His father, Timoteo, died seven months after his birth. His mother, Luigia Ferrari, directed him to studies, and at the age of 11 he was accepted as a boarder in the Royal School of Music, where he was...

 to conjecture in 1889 and 1909 that all the continents had once been joined into a supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...

 (now known as Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....

); Wegener noted the similarity of Mantovani's and his own maps of the former positions of the southern continents. Through volcanic
Volcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....

 activity due to thermal expansion
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...

 this continent broke and the new continents drifted away from each other because of further expansion of the rip-zones, where the oceans now lie. This led Mantovani to propose an Expanding Earth theory which has since been shown to be incorrect.

Some sort of continental drift without expansion was proposed by Frank Bursley Taylor
Frank Bursley Taylor
Frank Bursley Taylor was an American geologist, the son of a lawyer in Fort Wayne, Indiana. He was a Harvard dropout who studied privately financed in large part by his wealthy father...

, who suggested in 1908 (published in 1910) that the continents were dragged towards the equator by increased lunar gravity during the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

, thus forming the Himalayas and Alps on the southern faces. Wegener said that of all those theories, Taylor's, although not fully developed, had the most similarities to his own.

Wegener was the first to use the phrase "continental drift" (1912, 1915) (in German "die Verschiebung der Kontinente" – translated into English in 1922) and formally publish the hypothesis that the continents had somehow "drifted" apart. Although he presented much evidence for continental drift, he was unable to provide a convincing explanation for the physical processes which might have caused this drift. His suggestion that the continents had been pulled apart by the centrifugal pseudoforce (Polflucht) of the Earth's rotation or by a small component of astronomical precession
Precession
Precession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...

 was rejected as calculations showed that the force was not sufficient. The Polflucht
Polflucht
Polflucht is a geophysical concept invoked 1915 by Alfred Wegener to explain his ideas of Continental drift...

 hypothesis was also studied by Paul Sophus Epstein
Paul Sophus Epstein
Paul Sophus Epstein was a Russian-American mathematical physicist...

 in 1920 and found to be implausible.

Evidence that continents 'drift'

Evidence for continental drift is now extensive. Similar plant and animal fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s are found around different continent shores, suggesting that they were once joined. The fossils of Mesosaurus
Mesosaurus
Mesosaurus is an extinct genus of reptile from the Early Permian of southern Africa and South America. Along with the genus Stereosternum, it is a member of the family Mesosauridae and the order Mesosauria. Mesosaurus was one of the first marine reptiles, and had many adaptations to a fully...

, a freshwater reptile rather like a small crocodile, found both in Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

 and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

, are one example; another is the discovery of fossils of the land reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

 Lystrosaurus
Lystrosaurus
Lystrosaurus was a genus of Late Permian and Early Triassic Period dicynodont therapsids, which lived around 250 million years ago in what is now Antarctica, India, and South Africa...

from rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

s of the same age from locations in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

, Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

, and Antarctica. There is also living evidence — the same animals being found on two continents. Some earthworm
Earthworm
Earthworm is the common name for the largest members of Oligochaeta in the phylum Annelida. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female...

 families (e.g.: Ocnerodrilidae, Acanthodrilidae, Octochaetidae) are found in South America and Africa, for instance.

The complementary arrangement of the facing sides of South America and Africa is obvious, but is a temporary coincidence. In millions of years, slab pull
Slab pull
The Slab pull force is a tectonic plate force due to subduction. Plate motion is partly driven by the weight of cold, dense plates sinking into the mantle at trenches. This force and the slab suction force account for most of the overall force acting on plate tectonics, and the ridge push force...

 and ridge-push
Ridge-push
Ridge push or sliding plate force is a proposed mechanism for plate motion in plate tectonics. Because mid-ocean ridges lie at a higher elevation than the rest of the ocean floor, gravity causes the ridge to push on the lithosphere that lies farther from the ridge.As molten magma rises at a...

, and other forces of tectonophysics
Tectonophysics
Tectonophysics, a branch of geophysics, is the study of the physical processes that underlie tectonic deformation. The field encompasses the spatial patterns of stress, strain, and differing rheologies in the lithosphere and asthenosphere of the Earth; and the relationships between these patterns...

 will further separate and rotate those two continents. It was this temporary feature which inspired Wegener to study what he defined as continental drift, although he did not live to see his hypothesis become generally accepted.

Widespread distribution of Permo-Carboniferous
Permo-Carboniferous
The Permo-Carboniferous refers to the time period including the latter parts of the Carboniferous and early part of the Permian period. Permo-Carboniferous rocks are in places not differentiated because of the presence of transitional fossils, and also where no conspicuous stratigraphic break is...

 glacial sediments in South America, Africa, Madagascar, Arabia, India, Antarctica and Australia was one of the major pieces of evidence for the theory of continental drift. The continuity of glaciers, inferred from oriented glacial striations and deposits called tillites, suggested the existence of the supercontinent of Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...

, which became a central element of the concept of continental drift. Striations indicated glacial flow away from the equator and toward the poles, in modern coordinates, and supported the idea that the southern continents had previously been in dramatically different locations, as well as contiguous with each other.

Rejection of Wegener's theory, and subsequent vindication

While it is now accepted that the continents do move across the Earth's surface – though more in a driven mode than the aimlessness suggested by "drift" – as a theory, continental drift was not accepted for many years. One problem was that a plausible driving force was missing. And it did not help that Wegener was not a geologist.

The British geologist Arthur Holmes
Arthur Holmes
Arthur Holmes was a British geologist. As a child he lived in Low Fell, Gateshead and attended the Gateshead Higher Grade School .-Age of the earth:...

 championed the theory of continental drift at a time when it was deeply unfashionable. He proposed that the Earth's mantle contained convection cells that dissipated radioactive heat and moved the crust at the surface. His Principles of Physical Geology, ending with a chapter on continental drift, was published in 1944.

As late as 1953 – just five years before Carey
Samuel Warren Carey
Samuel Warren Carey AO was an Australian geologist who was an early advocate of the theory of continental drift. His work on plate tectonics reconstructions led him to develop the Expanding Earth hypothesis.- Biography :Carey was born in New South Wales and grew up on a farm three miles from...

 introduced the theory of plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

 – the theory of continental drift was rejected by the physicist Scheiddiger on the following grounds.
  • First, it had been shown that floating masses on a rotating geoid would collect at the equator, and stay there. This would explain one, but only one, mountain building episode between any pair of continents; it failed to account for earlier orogenic episodes.
  • Second, masses floating freely in a fluid substratum, like icebergs in the ocean, should be in isostatic equilibrium (where the forces of gravity and buoyancy are in balance). Gravitational measurements were showing that many areas are not in isostatic equilibrium.
  • Third, there was the problem of why some parts of the Earth's surface (crust) should have solidifed while other parts were still fluid. Various attempts to explain this foundered on other difficulties.


Geophysicist Jack Oliver is credited with providing seismologic evidence supporting plate tectonics which encompassed and superseded continental drift with “Seismology and the New Global Tectonics,” published in 1968, using data collected from seismologic stations, including those he set up in the South Pacific.

It is now known that there are two kinds of crust, continental crust
Continental crust
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...

 and oceanic crust
Oceanic crust
Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...

. Continental crust is inherently lighter and of a different composition to oceanic crust, but both kinds reside above a much deeper fluid mantle. Oceanic crust is created at spreading centers
Seafloor spreading
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics....

, and this, along with subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

, drives the system of plates in a chaotic manner, resulting in continuous orogeny
Orogeny
Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...

 and areas of isostatic imbalance. The theory of plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

explains all this, including the movement of the continents, better than Wegener's theory.

External links

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