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2: Plate Tectonics

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    Revolution is a word usually reserved for significant political or social changes. Several of these idea revolutions forced scientists to re-examine their entire field, triggering a paradigm shift that shook up their conventionally held knowledge. Charles Darwin’s book on evolution, On the Origin of Species, published in 1859; Gregor Mendel’s discovery of the genetic principles of inheritance in 1866; and James Watson, Francis Crick, and Rosalind Franklin’s model for the structure of DNA in 1953 did that for biology. Albert Einstein’s relativity and quantum mechanics concepts in the early twentieth century did the same for Newtonian physics.

    The concept of plate tectonics was just as revolutionary for geology. The theory of plate tectonics attributes the movement of massive sections of the Earth’s outer layers with creating earthquakes, mountains, and volcanoes. Many earth processes make more sense when viewed through the lens of plate tectonics. Because it is so important in understanding how the world works, plate tectonics is the first topic of discussion in this textbook.

    The map shows types of plate boundaries around the world and movement direction,
    Figure \(\PageIndex{1}\): Detailed map of all known plates, their boundaries, and movements.

    • 2.1: Alfred Wegener’s Continental Drift Hypothesis
      Alfred Wegener (1880-1930) was a German scientist who specialized in meteorology and climatology. His knack for questioning accepted ideas started in 1910 when he disagreed with the explanation on how the land bridge that connects Alaska and Asia formed. After reviewing the scientific literature, he published a hypothesis stating the continents were originally connected and then drifted apart.
    • 2.2: Layers of the Earth
      In order to understand the details of plate tectonics, it is essential to first understand the layers of the earth. In general, the Earth can be divided into layers based on chemical composition and physical characteristics.
    • 2.3: Convergent Boundaries
      Convergent boundaries, also called destructive boundaries, are places where two or more plates move toward each other. Convergent boundary movement is divided into two types, subduction and collision, depending on the density of the involved plates. Subduction involves an oceanic plate diving down into the mantle and producing a melt. Collision involves continental crust smashing into other continental crust.
    • 2.4: Divergent Boundaries
      At divergent boundaries, sometimes called constructive boundaries, lithospheric plates move away from each other. There are two types of divergent boundaries, categorized by where they occur: continental rift zones and mid-ocean ridges. Continental rift zones occur in weak spots in the continental plate. A mid-ocean ridge usually originates in a continental plate that expands to the point of splitting the plate apart, with seawater filling in the gap.
    • 2.5: Transform Boudaries
      A transform boundary is where the lithospheric plates slide past each other in the horizontal plane. This movement is described based on the perspective of an observer standing on one of the plates, looking across the boundary at the opposing plate. The plate moves either left or right relative to the one the observer is standing on.
    • 2.6: Hotspots
      To analyze plate movement, scientists study hotspots. A hotspot is an area in the lithospheric plate where molten magma breaks through and creates a volcanic center, islands in the ocean and mountains on land.

    Summary

    Plate tectonics is a unifying theory; it explains nearly all of the major geologic processes on Earth. Since its early inception in the 1950s and 1960s, geologists have been guided by this revolutionary perception of the world. The theory of plate tectonics states the surface layer of the Earth is broken into a network of solid, relatively brittle plates. Underneath the plates is a much hotter and more ductile layer that contains zones of convective upwelling generated by the interior heat of Earth. These convection currents move the surface plates around—bringing them together, pulling them apart, and shearing them side-by-side. Earthquakes and volcanoes form at the boundaries where the plates interact, with the exception of volcanic hotspots, which are not caused by plate movement.

    Thumbnail: Pangea map, with names of the continents. (CC-BA-SA 3.0; LucasVB).

    This page titled 2: Plate Tectonics is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Chris Johnson, Matthew D. Affolter, Paul Inkenbrandt, & Cam Mosher (OpenGeology) via source content that was edited to the style and standards of the LibreTexts platform.