Mechanism Involved in Plate Motion
Mechanism Involved in Plate Motion
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Continental Drift Theory
The Continental Drift Theory proposes that Earth’s continents were once joined together as a single large landmass and have slowly moved apart over millions of years. This idea was introduced in 1912 by the German scientist Alfred Wegener. Wegener suggested that the continents were originally part of a supercontinent called Pangaea, which later broke apart and drifted to their current positions.
Wegener supported his theory using several types of evidence, such as the matching shapes of continental coastlines, similar fossils found on widely separated continents, and comparable rock formations and ancient climate evidence. For example, the coastlines of South America and Africa appear to fit together like puzzle pieces.
https://education.nationalgeographic.org/resource/continental-drift/
However, when the theory was first proposed, many scientists rejected it because Wegener could not explain how the continents were able to move across the ocean floor. At that time, there was no known mechanism strong enough to move entire continents. Because of this missing explanation, the continental drift theory was widely criticized and not fully accepted by the scientific community.
Mechanism involved in Plate Motion
Convection Current
The splitting apart of large slabs of Earth's lithosphere, known as tectonic plates, is a geologic process called seafloor spreading or seafloor spreading theory. This process, along with other tectonic activities, is caused by mantle convection, which is the slow, churning motion of Earth’s mantle. Heat is transferred from the lower mantle and core to the lithosphere by convection currents. Additionally, these currents facilitate the "recycling" of lithospheric materials back to the mantle.
At divergent plate boundaries, seafloor spreading takes place as tectonic plates gradually move apart. The heat from convection currents in the mantle causes the crust to become more malleable and less dense.
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The less dense material rises, often creating a mountain or elevated area on the seafloor. Over time, the crust fractures, allowing hot magma, driven by mantle convection (convection current), to rise and fill these cracks before spilling onto the crust. This magma is then cooled by cold seawater, forming igneous rock. This rock, known as basalt, becomes a new component of Earth's crust.
Ridge Push and Slab Pull
https://giphy.com/gifs/plate-tectonics-ridge-push-slab-pull-7vAR1jVqfyovyW4fuq
The motion of oceanic plates is believed to be predominantly driven by 'Ridge Push' and 'Slab Pull'. Ridge push originates from the potential energy gradient created by the high elevation of the ridges. It describes the process by which new oceanic lithosphere (the rigid outer layer of the Earth) forms at mid- ocean ridges and then slides down the flanks of the ridge due to gravitational forces. Meanwhile, slab pull results from the negative buoyancy of the subducting plate. It is the process by which the sinking of a dense, oceanic lithospheric plate into the mantle at a subduction zone pulls the rest of the plate along with it. This force is considered to be one of the most significant in the movement and deformation of Earth’s lithosphere.
Plate Tectonic Theory as a Unifying Theory
The development of plate tectonic theory is a landmark in the history of geology, evolving over several centuries through a series of crucial observations, hypotheses, and technological advancements. In the 16th century, early observers like Abraham Ortelius suggested that continents might have once been joined. This idea gained scientific footing in the early 20th century with Alfred Wegener's hypothesis of continental drift, which posited that continents were part of a supercontinent (Pangaea) that fragmented and drifted apart. Despite compelling evidence, such as the matching coastlines of South America and Africa and similar fossil records across continents, Wegener's theory was initially dismissed due to the lack of a plausible mechanism for continental movement. The mid-20th century brought significant advances in oceanography, particularly through the work of Marie Tharp and Bruce Heezen, who mapped the ocean floor and revealed the existence of mid-ocean ridges and deep-sea trenches. This, combined with Harry Hess's theory of seafloor spreading, provided a mechanism for the movement of oceanic crust. Paleomagnetic studies further bolstered the theory by showing symmetrical magnetic stripes on the ocean floor, indicating periodic reversals of Earth's magnetic field and confirming seafloor spreading. The unification of these ideas into the modern plate tectonic theory came in the late 1960.
The plate tectonic theory is a scientific theory that describes the Earth's lithosphere (the outermost layer of the Earth) as being divided into several large and small plates that float on the semi-fluid asthenosphere below. It is regarded as a "unifying theory" in geology because it integrates the work and theories of the majority of other geological disciplines. Plate motions explain how mountains, deep-sea trenches, volcano chains, island arcs, and rift valleys form. Plate tectonic theory combines the concepts of seafloor spreading, subduction, and mantle convection.
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