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Plate tectonics (from Latin tectonicus, from Ancient Greek τεκτονικός (tektonikós) 'pertaining to building') 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.

Plate tectonics came to be accepted by geoscientists after seafloor spreading was validated in the mid- to late 1960s. The processes that result in plates and shape Earth's crust are called tectonics. Earth's lithosphere, the rigid outer shell of the planet including the crust and upper mantle, is fractured into seven or eight major plates (depending on how they are defined) and many minor plates or "platelets". Where the plates meet, their relative motion determines the type of plate boundary (or fault): convergent, divergent, or transform. Tectonic plates are composed of the oceanic lithosphere and the thicker continental lithosphere, each topped by its own kind of crust. Along convergent plate boundaries, the process of subduction carries the edge of one plate down under the other plate and into the mantle. The lost surface is balanced by the formation of new oceanic crust along divergent margins by seafloor spreading, keeping the total surface area constant in a tectonic "conveyor belt". While Earth is the only planet known to currently have active plate tectonics, evidence suggests that other planets and moons have experienced or exhibit forms of tectonic activity. Jupiter's moon Europa shows signs of ice crustal plates moving and interacting, similar to Earth's plate tectonics. Mars and Venus are thought to have had tectonic activity in the past, though not of the same form as Earth. At a seafloor spreading ridge, plates move away from the ridge, which is a topographic high, and the newly formed crust cools as it moves away, increasing its density and contributing to the motion. At a subduction zone, the relatively cold, dense oceanic crust sinks down into the mantle, forming the downward convecting limb of a mantle cell, which is the strongest driver of plate motion.

However, in the plate tectonics context (accepted since the seafloor spreading proposals of Heezen, Hess, Dietz, Morley, Vine, and Matthews (see below) during the early 1960s), the oceanic crust is suggested to be in motion with the continents, which caused the proposals related to Earth rotation to be reconsidered.

The other forces are only used in global geodynamic models not using plate tectonics concepts (therefore beyond the discussions treated in this section) or proposed as minor modulations within the overall plate tectonics model.

One method of dealing with this problem is to consider the relative rate at which each plate is moving as well as the evidence related to the significance of each process to the overall driving force on the plate.

After all these considerations, plate tectonics (or, as it was initially called "New Global Tectonics") became quickly accepted and numerous papers followed that defined the concepts:

According to a hypothesis proposed by Robert Stern and Taras Gerya, plate tectonics are a necessary criterion for a planet to be able to sustain complex life because of the role plate tectonics plays in regulating the carbon cycle.

Modern plate tectonics are suggested to have emerged by at least 2.2 billion years ago with the formation of the first recognised supercontinent Columbia, though some authors have suggested that modern-style plate tectonics did not appear until 800 million years ago based on the late appearance of rock types like blueschist which require cold subducted material.

The appearance of plate tectonics on terrestrial planets is related to planetary mass, with more massive planets than Earth expected to exhibit plate tectonics.

However, in 2007, two independent teams of researchers came to opposing conclusions about the likelihood of plate tectonics on larger super-Earths with one team saying that plate tectonics would be episodic or stagnant and the other team saying that plate tectonics is very likely on super-earths even if the planet is dry.

Quick Facts

• Along convergent plate boundaries, the process of subduction carries the edge of one plate down under the other plate and into the mantle.
• While Earth is the only planet known to currently have active plate tectonics, evidence suggests that other planets and moons have experienced or exhibit forms of tectonic activity.
• The processes that result in plates and shape Earth's crust are called tectonics.
• Jupiter's moon Europa shows signs of ice crustal plates moving and interacting, similar to Earth's plate tectonics.
• Plate tectonics came to be accepted by geoscientists after seafloor spreading was validated in the mid- to late 1960s.

Source material: Wikipedia - "Plate tectonics". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.