Plate Tectonics

Plate tectonic theory is a shared understanding that encapsulates our current understanding of geologic processes. 

  • Plate tectonic processes serve as the major driver of the transformations of rock materials represented in the traditional rock cycle. Plate tectonics drive the evolution of Earth’s surface features and materials by fractionating material by chemical, mineralogical, and physical properties (ES.7 a). 

  • Earth’s interior is in constant motion through the process of convection (ES.7 a).  Earth consists of a solid, mostly iron inner core; a liquid, mostly iron outer core; a crystalline but largely plastic mantle; and a rocky, brittle crust (ES.7 a).  

  • Earth's geomagnetic field is thought to be created as a result of electric currents generated by convection of molten iron and nickel in the outer core. Heat flow, Earth’s rotation, and the existence of a solid inner core influence the convection driven dynamo (ES.7 a).  

  • The geomagnetic field imprints a magnetic signature in crystallizing igneous rock, thus leaving information that can be used to determine the motion and latitude of the Earth’s crust over time. Scientific evidence shows that Earth's geomagnetic field reverses itself periodically (a). The large-scale plate tectonic processes (e.g., subduction, island arc formation, continental collisions, and orogeny) occurring at and near plate boundaries are responsible for significant transformations of Earth materials (ES.5 d).



The cycling of energy and matter in Earth’s interior occurs through the process of convection and has important consequences for Earth’s surface.

  • Plate motion occurs due to convection in Earth’s mantle, including upwelling of material from the deep mantle in rift zones, the lateral movement of tectonic plates, and the pull of sinking dense, old plates at subduction zones (ES.7 b).

  • Earth’s tectonic plates consist of the rocky crust and uppermost mantle and move slowly in respect to one another (ES.7 b). 

  • Earth’s lithosphere is divided into plates that are in motion with respect to one another. The lithosphere is composed of the crust and upper portion of the mantle. There are two different types of lithospheres—oceanic and continental— that have very different physical and mineralogical characteristics. The ocean lithosphere is relatively thin, young, and dense. The continental lithosphere is relatively thick, old, and less dense (ES.7 b).



The cycling of energy and matter in Earth’s interior occurs through the process of convection and has important consequences for ocean topography. 

  • The topography of the seafloor is at least as variable as that on the continents. Features of the seafloor that are related to plate tectonic processes include mid-ocean ridges and trenches (ES.10 d).


  • Most large scale, high-energy events of geologic activity (e.g., earthquakes, volcanoes, and mountain building) occur as a result of relative motion along plate boundaries (ES.7 c). 

  • Relative plate motions and plate boundaries are convergent (subduction and continental collision), divergent (seafloor spreading), or transform. Major features of convergent boundaries include collision zones (folded and thrust faulted mountains) and subduction zones (volcanoes and trenches). Major features of divergent boundaries include mid-ocean ridges, rift valleys, fissure volcanoes, and flood lavas. Major features of transform boundaries include strike-slip faults (ES.7 c).

  • All plate boundaries show earthquake activity of varying energy levels and depths (ES.7 c).

  • A volcano is an opening where magma erupts onto Earth’s surface as lava and/or other extrusive material. Most volcanic activity is associated with plate boundaries: subduction, rifting, or seafloor spreading. Hot spot volcanic activity, such as the volcanic islands of Hawaii, is exceptional in that it is not related to plate boundaries. A hot spot is thought to be derived from a deep, localized heat source known as a mantle plume, though there is some scientific debate on this (ES.7 c).

  •  A fault is a break or crack in Earth’s crust along which movement has occurred (ES.7 c).  

  • Topographic maps and satellite imagery are 2-D models that provide information defining 3-D landforms. They contain extensive information related to geographic as well as human structures and changes to the land surface and are useful in understanding geologic processes (ES.7 c).


Earth’s atmosphere is comprised of interacting and interdependent elements that are subject to change in response to inputs and outflows of energy and matter.  

  • Earth’s atmosphere is 21 percent oxygen, 78 percent nitrogen, and one percent trace gases. The composition of the atmosphere can change due to human, biologic, and geologic activity (ES.11 a).  



The cycling of energy and matter through various natural and manmade processes have led to changes in the composition of Earth’s atmosphere.  

  • Evolution, including the origination and extinction of species, has altered the composition of gases in the atmosphere (ES.11 b).  

  • The composition of Earth’s atmosphere has changed over geologic time. Earth’s atmosphere is unique in the solar system in that it contains substantial oxygen (ES.11 b).  

  • Earth’s most primitive atmosphere may have been comprised of mainly helium and hydrogen.; however, it is unclear whether Earth had an atmosphere at its formation due to radiation from the young sun. Scientific evidence suggests that Earth’s early atmosphere contained mostly CO2, CO, nitrogen, SO2, and water vapor, resulting from volcanic outgassing. This atmosphere was then modified by early photosynthetic life (ES.11 b).

  • The atmospheres of Earth, Mars, and Venus apparently had very different paths toward the evolution of their current conditions. Many factors may have influenced this, including distance from the sun, planetary mass, the nature of the planets’ interiors, the presence of a large moon, and the origin and nature of each planet’s early atmosphere (ES.11 b).  

  • Early photosynthetic life such as cyanobacteria (blue-green algae) consumed carbon dioxide and generated oxygen. It was only after early photosynthetic life generated oxygen that animal life became possible (ES.11 b).


Earth’s rocks and fossils document the existence, diversity, extinction, and change of many life forms and their environment through Earth’s history.  

  • The history of Earth and the ages of rocks can be investigated and understood by studying rocks and fossils (ES.9 a).  

  • Evidence of ancient, often extinct life is preserved in many sedimentary rocks. A fossil is the remains, impression, or other evidence preserved in rock of the former existence of life. Fossil evidence indicates that life forms have changed and become more complex over geologic time. Some ways in which fossils can be preserved are molds, casts, and original bone or shell (ES.9 a). 



Technological advances, breakthroughs in interpretation, and new observations continuously refine our understanding of Earth.

  • Relative time places events in a sequence without assigning any numerical ages. Fossils, superposition, and cross-cutting relations are used to determine the relative ages of rocks (ES.9 b).  

  • Absolute time places a numerical age on an event. Radiometric dating is used to determine the absolute age of rocks by measuring the products of radioactive decay of certain elements (ES.9 c). 



Explanations of stability and change in natural systems can be constructed by examining changes over time. Evidence, in the form of rocks and fossils from different geologic periods and epochs, has been found in Virginia. 

  • In Virginia, fossils are found mainly in the Coastal Plain, Valley and Ridge, and Appalachian Plateau provinces. Most Virginia fossils are of marine organisms. This indicates that large areas of the state have been periodically covered by seawater (ES.9 d).  

  • Paleozoic, Mesozoic, and Cenozoic fossils are found in Virginia (ES.9 d).




Basic Study Guide

  • Plate Tectonic Theory: Understanding geological processes driving changes in Earth's surface features.
      - Driving Forces: Plate tectonic processes drive the rock cycle through fractionation by chemical, mineralogical, and physical properties.
      - Earth's Interior:
        - Composed of a solid inner core, molten outer core, plastic mantle, and brittle crust.
        - Motion due to convection affects geological activity.
      - Geomagnetic Field:
        - Generated by convection currents in the outer core of molten iron/nickel.
        - Influenced by heat flow, Earth’s rotation, and the inner core.
        - Records magnetic signatures in igneous rock aiding in determining historical crust movement.
        - Field experiences periodic reversals.
      - Plate Movement:
        - Caused by convection in the mantle, plate interactions (subduction, rifting), and the descent of old plates.
        - Lithosphere consists of the crust and upper mantle, divided into oceanic (thin, dense) and continental (thick, less dense) plates.
      - Seafloor Topography:
        - Comparable variability to continental features (e.g. ridges and trenches).
      - Geologic Activity:
        - Major geological events like earthquakes and volcanic activity arise from plate boundary interactions.
        - Types of boundaries:
          - Convergent: Subduction and continental collision (mountains, volcanoes).
          - Divergent: Seafloor spreading (mid-ocean ridges, rift valleys).
          - Transform: Strike-slip faults.
      - Volcanic Activity:
        - Associated with plate boundaries, sometimes from hot spots (e.g., Hawaii).
      - Faults:
        - Breaks/cracks in the crust where movement occurs.
        - Topographic maps (2-D models) help define 3-D landforms and monitor changes.
      - Atmospheric Composition:
        - 21% oxygen, 78% nitrogen, and trace gases; changing due to various activities.
      - Evolution of Atmosphere:
        - Ancient atmosphere likely made of helium and hydrogen; volcanic outgassing contributed CO2, CO, nitrogen, SO2, and water vapor.