When Did Plate Tectonics Begin?
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Earth is the only planet with plate tectonics http://www.ucmp.berkeley.edu/geology/tectonics.html , and it is controversial why and when this began. Some argue that plate tectonics already operated in Archean times (>2.5 billion years ago, or Ga) whereas others argue for a much later beginning. The thermal history of the cooling Earth must be important. Numerical experiments show that the thermal boundary layer of the Earth, the lithosphere, controls mantle convection today. We now understand that the sinking of dense lithosphere in subduction zones is responsible for plate motions and seafloor spreading and is the principal way that Earth cools. The hotter early Earth may have had a weaker and less dense lithosphere and so had a different style of mantle convection. This theoretical background is essential to provide context for empirical (field and lab analyses) results. Demonstrating that plate tectonics operated at any given time requires evidence for subduction and for independent plate motions and rotations. Therefore, understanding when plate tectonics began depends on determining when the present mode of subduction and independent plate motions and rotations began.

Understanding when and why plate tectonics began is one of the most important unresolved problems in our understanding of the Earth, and progress towards resolving it will require a creative, interdisciplinary, and international effort. This requires exploring both theoretical and empirical constraints on when the modern regime of plate tectonics began on Earth. Theoretical considerations include modelling Earth's thermal history, understanding what powers the plates and evaluating how earth's cooling affected these forces. Empirical considerations should focus on identifying what are the best ways to recognize plate tectonics in the geologic record. Proxies for plate motion or operation of subduction zones and ocean ridges, including paleomagnetism, isotopic and trace element compositions of igneous rocks, styles of deformation, the temporal distribution of hallmarks of subduction (ophiolites, blueschists, eclogites and diamond- and coesite-bearing ultra-high pressure assemblages) and secular distribution of associations diagnostic of plate tectonics such as passive margin sequences and arc magmatic assemblages.

 From June 14 to 18, 2006 a Geological Society of America Penrose Conference was held in Lander, Wyoming addressing these questions of when plate tectonics began in Earth history (http://www.geosociety.org/penrose/06-tectonicsBegin.htm ;Nature Article; GSA Today Article). The presentations on this website are from that meeting. They are listed below in the order they were given. Some of these presentations are very short, because only a few minutes were available for presentations. Interested parties should contact presenters directly if they have questions. For questions or comments about the content of this website, please contact R.J. Stern rjstern@utdallas.edu ; to notify us of problems with the website, please contact Mr. Dean Tuck utdrockjock@gmail.com .


Last Update: 10/4/2006