Continental drift is the theory, originating in the early 20th century, that Earth's continents move or drift relative to each other over geologic time. The theory of continental drift has since been validated and incorporated into the science of plate tectonics, which studies the movement of the continents as they ride on plates of the Earth's lithosphere.
Plate tectonics is the scientific theory that Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. Plate tectonics came to be accepted by geoscientists after seafloor spreading was validated in the mid-to-late 1960s.
Seafloor spreading, or seafloor spread, 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.
A lithosphere is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time scales of up to thousands of years or more. The crust and upper mantle are distinguished on the basis of chemistry and mineralogy.
Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second plate, the heavier plate dives beneath the other and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with rates of convergence as high as 11 cm/year.
Isostasy or isostatic equilibrium is the state of gravitational equilibrium between Earth's crust and mantle such that the crust "floats" at an elevation that depends on its thickness and density. This concept is invoked to explain how different topographic heights can exist at Earth's surface. Although originally defined in terms of continental crust and mantle, it has subsequently been interpreted in terms of lithosphere and asthenosphere, particularly with respect to oceanic island volcanoes, such as the Hawaiian Islands.
Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle along the subduction zone. They are the principal way by which continental growth is achieved.
Harry Hammond Hess was an American geologist and a United States Navy officer in World War II who is considered one of the "founding fathers" of the unifying theory of plate tectonics. He published theories on sea floor spreading, specifically on relationships between island arcs, seafloor gravity anomalies, and serpentinized peridotite, suggesting that the convection in the Earth's mantle is the driving force behind this process.
Continental crust is the layer of igneous, metamorphic, and sedimentary rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its bulk composition is richer in aluminium silicates (Al-Si) and has a lower density compared to the oceanic crust, called sima which is richer in magnesium silicate (Mg-Si) minerals. Changes in seismic wave velocities have shown that at a certain depth, there is a reasonably sharp contrast between the more felsic upper continental crust and the lower continental crust, which is more mafic in character.
Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the rigid uppermost layer of the mantle. The crust and the rigid upper mantle layer together constitute oceanic lithosphere.
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about 2,600 meters (8,500 ft) and rises about 2,000 meters (6,600 ft) above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a divergent plate boundary. The rate of seafloor spreading determines the morphology of the crest of the mid-ocean ridge and its width in an ocean basin.
The expanding Earth or growing Earth was a hypothesis attempting to explain the position and relative movement of continents by increase in the volume of Earth. With the recognition of plate tectonics in 20th century, the idea has been abandoned.
Pangaea or Pangea was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million years ago, and began to break apart about 200 million years ago, at the end of the Triassic and beginning of the Jurassic. Pangaea was C-shaped, with the bulk of its mass stretching between Earth's northern and southern polar regions and surrounded by the superocean Panthalassa and the Paleo-Tethys and subsequent Tethys Oceans. Pangaea is the most recent supercontinent to have existed and the first to be reconstructed by geologists.
Plate reconstruction is the process of reconstructing the positions of tectonic plates relative to each other or to other reference frames, such as the Earth's magnetic field or groups of hotspots, in the geological past. This helps determine the shape and make-up of ancient supercontinents and provides a basis for paleogeographic reconstructions.
The evolution of tectonophysics is closely linked to the history of the continental drift and plate tectonics hypotheses. The continental drift/ Airy-Heiskanen isostasy hypothesis had many flaws and scarce data. The fixist/ Pratt-Hayford isostasy, the contracting Earth and the expanding Earth concepts had many flaws as well.
Warren B. Hamilton was an American geologist known for integrating observed geology and geophysics into planetary-scale syntheses describing the dynamic and petrologic evolution of Earth's crust and mantle. His primary career (1952–1995) was as a research scientist with the US Geological Survey (USGS) in geologic, then geophysical, branches. After retirement, he became a Distinguished Senior Scientist in the Department of Geophysics, Colorado School of Mines (CSM). He was a member of the National Academy of Sciences, and a holder of the Penrose Medal, highest honor of the Geological Society of America (GSA). Hamilton served in the US Navy from 1943 to 1946, completed a bachelor's degree at the University of California, Los Angeles (UCLA) in a Navy training program in 1945, and was a commissioned officer on the aircraft carrier USS Tarawa. After returning to civilian life, he earned an MSc in geology from the University of Southern California in 1949, and a PhD in geology from UCLA in 1951. He married Alicita V. Koenig (1926–2015) in 1947. Hamilton died in October 2018 at the age of 93; until the last few weeks he was working on new research. His final paper, "Toward a myth-free geodynamic history of Earth and its neighbors," was published posthumously (2019) in Earth-Science Reviews. In 2022 the Geological Society of America published an edited volume in his honor, with 33 papers: In the Footsteps of Warren B. Hamilton: New Ideas in Earth Science. The first chapter of this book describes how Hamilton's last paper was written; the second applies Thomas Kuhn's model of scientific change to interpreting Hamilton's career.
The Plate Tectonics Revolution was the scientific and cultural change which developed from the acceptance of the plate tectonics theory. The event was a paradigm shift and scientific revolution.
Ridge push is a proposed driving force for plate motion in plate tectonics that occurs at mid-ocean ridges as the result of the rigid lithosphere sliding down the hot, raised asthenosphere below mid-ocean ridges. Although it is called ridge push, the term is somewhat misleading; it is actually a body force that acts throughout an ocean plate, not just at the ridge, as a result of gravitational pull. The name comes from earlier models of plate tectonics in which ridge push was primarily ascribed to upwelling magma at mid-ocean ridges pushing or wedging the plates apart.
Kevin C. A. Burke was a geologist known for his contributions in the theory of plate tectonics. In the course of his life, Burke held multiple professorships, most recent of which (1983-2018) was the position of professor of geology and tectonics at the Department of Earth and Atmospheric Science, University of Houston. His studies on plate tectonics, deep mantle processes, sedimentology, erosion, soil formation and other topics extended over several decades and influenced multiple generations of geologists and geophysicists around the world.
Otto Ampferer was an Austrian alpinist and geologist. To explain the complex processes of Orogeny, he developed his "theory of undercurrent" with the idea of a partially plastic deep Earth's crust (asthenosphere). He became – even before Alfred Wegener – the pioneer of the modern view of continental drift.
