New Theory Regarding Earth’s Lithospheric Plates
The theory of plate tectonics, proposed by Alfered Wegener, states that Earth’s lithosphere— its solid outer crust—“is separated into plates that move over the asthenosphere, the molten upper portion of the mantle. Oceanic and continental plates come together, spread apart, and interact at boundaries all over the planet” (3). The interaction between tectonic plates and their boundaries results in many of Earth’s landforms, such as volcanoes, mountains, oceanic ridges, and rift valleys. When plates collide, which is called a convergent plate boundary, one plate is either subducted and joins the Earth’s mantle again. When two continental plates collide, a mountain belt is normally formed. When plates diverge from each other, material from the mantle is upwelled, creating more oceanic crust (6). The subduction of old oceanic crust and the formation of new crust means that “very little continental crust remains from Earth’s early days, making it tricky to figure out when active plate tectonics started” (1). Due to this, geologists have had no concrete answer to what led to the creation of tectonic plates.
Dr. Alexander Webb of the University of Hong Kong has proposed that when Earth was a young planet, its outer shell heated up, and the expansion of the rock caused cracks that divided Earth’s lithosphere. Webb and his team have created a spherical model based on simulations tracking the deformation and stress experienced by the lithosphere enlarging (1). This new proposal is based on the abandoned “expanding Earth theory,” where the swelling of our planet is believed to cause major earthquakes and mountain building. The thermal expansion needed can be explained by early volcanic activity. The cooling of ejected magma on Earth’s surface means that the lithosphere’s cooler material left behind would be warmed via conduction of the underlying mantle (4).
Webb’s theory seems to oppose the physical principles of Earth science and call upon discredited ideas. For example, Earth’s main source of internal heat is the decay of radioactive isotopes, and as time goes on, there is less available heat (2). This information more coincides with thermal contraction of the planet rather than expansion. However, Webb’s theory of thermal expansion is slowly becoming more and more accepted by the scientific community, despite its conflict with our modern plate tectonics theory. Geodynamicist Taras Geyas says, “But even if we had a perfect understanding of modern plate tectonics, that wouldn’t necessarily tell us everything about how the process got started… An egg does not look like a chicken… Even if we look at the chicken from a thousand different perspectives, it will not help us imagine an egg” (1).
1. Caperton Morton, M. (2017, May 26). When and how did plate tectonics begin on Earth? Retrieved August 03, 2020, from https://www.earthmagazine.org/article/when-and-how-did-plate-tectonics-begin-earth
2. Choi, C. (2011, July 18). Radioactive Decay Fuels Earth's Inner Fires. Retrieved August 04, 2020, from https://www.livescience.com/15084-radioactive-decay-increases-earths-heat.html
3. Cowan, A. M. (2013, March 05). Plate Tectonics. Retrieved August 03, 2020, from https://www.nationalgeographic.org/media/plate-tectonics/
4. Malewar, A. (2020, July 20). How Earth's outer shell first broke into tectonic plates? Retrieved August 03, 2020, from https://www.techexplorist.com/earth-outer-shell-first-broke-tectonic-plates/33925/
5. O'Neill, M. (2020, July 24). "Breaking" News: How Earth's Outer Shell First Broke Into Tectonic Plates. Retrieved August 03, 2020, from https://scitechdaily.com/breaking-news-how-earths-outer-shell-first-broke-into-tectonic-plates/
6. Tarbuck, E. J., Lutgens, F. K., & Tasa, D. (2015). Earth science. Boston, MA: Pearson.