Plate Tectonics Quiz

Plate Tectonics: Earth's Lithosphere Movement

• Earth's lithosphere comprises of several tectonic plates that have been moving since 3.4 billion years ago.
• The lithosphere is broken into 7-8 major plates and several minor plates or "platelets."
• The relative motion of the plates determines the type of plate boundary.
• Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries.
• Tectonic plates are composed of oceanic lithosphere and the thicker continental lithosphere.
• The total geoid surface area of the lithosphere remains constant.
• Tectonic plates move because Earth's lithosphere has greater mechanical strength than the underlying asthenosphere.
• Plate movement is driven by the motion of the seafloor away from spreading ridges and density changes in the crust.
• Three types of plate boundaries exist: divergent, convergent, and transform.
• The main driving force behind tectonic plate motions is the excess density of the oceanic lithosphere sinking in subduction zones.
• Mantle convection directly and indirectly relates to plate motion.
• Gravity is invoked as the major driving force, through slab pull along subduction zones.The theory of Plate Tectonics has been developed over 50 years of scientific debate, with the acceptance of the theory itself being a scientific revolution.

Alfred Wegener proposed the idea of continental drift in 1912, which culminated in the modern theory of plate tectonics.

Wegener suggested that continents separated and drifted apart, likening them to "icebergs" of low density sial floating on a sea of denser sima.

Many distinguished scientists of the time were outspoken critics of continental drift, due to a lack of detailed evidence and a reasonable physically supported mechanism.

Paleomagnetism, data on the bathymetry of the deep ocean floors, and the nature of the oceanic crust supported the movement of lithospheric plates.

The theory of plate tectonics was defined in a series of papers between 1965 and 1967, revolutionizing the Earth sciences.

Plate motion is mostly driven by the weight of cold, dense plates sinking into the mantle at trenches, known as slab pull, and recent models indicate that trench suction plays an important role as well.

Driving forces related to Earth rotation, including tidal force, are still highly debated as possible principal driving forces of plate tectonics.

The vector of a plate's motion is a function of all the forces acting on the plate, and the degree to which each process contributes to the overall motion of each tectonic plate is still an active subject of research.

The significance of each process to the overall driving force on the plate varies depending on the geodynamic setting and the properties of each plate.

The history of the theory of plate tectonics involves a lively debate between "drifters" or "mobilists" and "fixists" during the 1920s, 1930s, and 1940s.Plate Tectonics: The Development of the Theory

• Continental drift theory was not initially taken seriously due to a lack of explanation for the mechanism behind it.

• Early geologists believed there were two types of crust, sial and sima, and that a static shell of strata was present under the continents.

• Abnormalities in plumb line deflection led to the concept of mountains having "roots" and the discovery of Wadati-Benioff zones.

• Paleomagnetic data supported the idea of polar wander, with the magnetic pole shifting over time.

• The hypothesis of an expansion of the global crust was proposed but was generally regarded as unsatisfactory.

• Seafloor spreading was confirmed through seismic instruments and the discovery of mid-oceanic ridges and magnetic striping patterns.

• The discovery of magnetic striping led to the seafloor spreading hypothesis and the Vine-Matthews-Morley hypothesis.

• Plate tectonics was quickly accepted in the scientific world, and numerous papers followed that defined the concepts.

• Continental drift theory helps biogeographers explain the disjunct biogeographic distribution of life on different continents.

• Plate reconstruction is used to establish past and future plate configurations and determine ancient supercontinents.

• Current plate boundaries are defined by their seismicity, while past plate boundaries are identified through evidence such as ophiolites.

• Tectonic motion is believed to have begun around 3 to 3.8 billion years ago, and past plate motions are constrained using various types of quantitative and semi-quantitative information.

• The movement of plates has caused the formation and break-up of continents over time, including the formation of supercontinents.Plate Tectonics on Earth and Other Celestial Bodies

• Rodinia was a supercontinent that formed about 1 billion years ago and broke up into eight continents around 600 million years ago.

• The Himalayas were formed by the collision of two major plates, and before uplift, they were covered by the Tethys Ocean.

• There are usually seven or eight "major" plates on Earth: African, Antarctic, Eurasian, North American, South American, Pacific, and Indo-Australian.

• There are dozens of smaller plates, the seven largest of which are the Arabian, Caribbean, Juan de Fuca, Cocos, Nazca, Philippine Sea, and Scotia.

• The current motion of the tectonic plates is determined by remote sensing satellite data sets calibrated with ground station measurements.

• Earth's tectonic activity is due to abundant water, and Venus shows no evidence of active plate tectonics because temperatures are too high for significant water to be present.

• Mars is considerably smaller than Earth and Venus, and there is evidence for ice on its surface and in its crust.

• Some of the satellites of Jupiter have features that may be related to plate-tectonic style deformation, and Europa shows the first sign of subduction activity on another world other than Earth.

• Titan, the largest moon of Saturn, was reported to show tectonic activity in images taken by the Huygens probe.

• Plate tectonics is more likely on Earth-sized planets if there are oceans of water, and it is part of the search for extraterrestrial intelligence and extraterrestrial life.

• Plate tectonics on terrestrial planets is related to planetary mass, with more massive planets than Earth expected to exhibit plate tectonics.

• Earth may be a borderline case, owing its tectonic activity to abundant water.