Editing Archean Eon (section)

== Plate Tectonics ==
The timing for the onset of plate tectonics is debated, but there is a consensus that some form of '''tectonic activity''' was occurring by at least 3.0 GYA, with some evidence suggesting it could have started as early as 4.0 GYA. Early tectonic activity would have been more akin to gradual movements or proto-plate tectonics, influenced by thermal gradients in the young Earth's mantle. Some of the earliest evidence for plate tectonics comes from '''greenstone belts''' and other rock assemblages, suggesting subduction-like processes were occurring. 

No later than 3 GYA, as plate tectonics had become a dominant Earth process, featuring the '''recycling''' of crustal material through subduction and the addition of new material from volcanic activity contributed to the growth of continental nuclei or '''cratons'''. These cratons are characterized by their thick '''lithosphere''' and old, rigid rock formations that have remained largely unchanged by tectonic processes for billions of years. The process by which these early crustal blocks became cratons is known as '''cratonization''', which involves the thickening of the lithosphere, often through tectonic processes such as the collision of crustal blocks, volcanic activity, and the accretion of sediments and other materials. Some of the rocks within are dated as early as 3.8 to 3.6 GYA.  

Today, cratons can be found at the core of all modern continents, including such well-known examples as the Canadian Shield in North America, the Baltic Shield in Europe, and the Kaapvaal Craton in southern Africa. 

Subduction zones not only generate new crustal material but also recycle older, denser crust back into the mantle. This recycling process is essential for the dynamic evolution of the Earth's surface. The movement of tectonic plates plays a crucial role in the formation and assembly of continents. Collisions between plates can lead to the formation of mountain ranges and the thickening of the crust, which contributes to the stability of continental regions.  

Several theories attempt to explain how plate tectonics started: 

* <u>Gravitational Sliding</u>: the cooling of the Earth's surface could have led to the formation of a rigid lithosphere that started to move over the more ductile asthenosphere beneath due to gravitational forces.
* <u>Mantle Convection</u>: as Earth cooled, convection currents within the mantle could have started to drag and break apart the crust into plates. The sinking of cooler, denser crust into the mantle at subduction zones and the rise of hot mantle material at mid-ocean ridges are key drivers of plate movements.
* <u>Incremental Assembly</u>: the process may have begun with smaller, proto-plates engaging in early subduction and accretion activities, gradually leading to the development of larger plates and more active tectonics.
While there was certainly movement and activity, the global-scale continental drift associated with the breakup and formation of supercontinents was not yet a feature of this early period. The interactions between proto-continents or cratons were more localized, without the extensive, ocean-spanning movements observed in later periods.