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Harmon's View on Plate Tectonics

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Plate Tectonics Predicting the Past

Plate tectonics is a relatively new concept, being introduced by Alfred Wegener in his 1915 publication of Origins of the Continents and Oceans, through his theory of continental drifts and not publicly accepted by the scientific world until the 1960s (Christopherson, 2011, p. 314). While Wegener’s theory wasn’t reputable until 50 years ago, studying plate tectonics can provide geologists a glimpse of Earth’s past by studying materials from Earth’s crust that have been brought to the surface (Harmon, 2011). Plate tectonics include the processes of upwelling of magma through volcanic activity, lithospheric plate movements, sea-floor spreading, subduction, and lithospheric deformation such as folding and faulting (Christopherson, 2011, p. 315). Katherine Harmon’s article in the Scientific American focuses on two geologists’ study of minerals compounded in diamonds that have been upwelled to Earth’s surface from the crust through volcanic activity and how those diamonds give insight to the origins of continental drift and supercontinents like Pangaea (Harmon, 2011).

Harmon uses a study from Steven Shirey, a geologist from the Carnegie Institution of Washington’s Department of Terrestrial Magnetism. Shirey’s study is founded on the idea that volcanoes bring ancient diamonds from hundreds of kilometers beneath Earth’s surface that can be used to provide information about the first continental drifts from lithospheric plates by tracing impurities in the diamonds (Harmon, 2011). Many plate boundaries are located in areas of high volcanic activity, like the “ring of fire” surrounding the Pacific Basin, making it plausible that diamonds and minerals from these areas are credible sources of information about the beginnings of plate tectonics before Pangaea (Christopherson, 2011, p.323). Diamonds used for Shirey’s study were formed under ancient intense pressure within the Earth’s crust and are brought tothe surface via volcanic eruptions. The minerals inside the marred diamonds begin to look different in the diamonds that date back to around 3 billion years ago. These diamonds contain traces of eclogite, a rock that would have been common within shallow melting of basalt, which is common in the mergence of thick, moving continents like the ones we see currently today. In response to these differences, Shirey says, “We are seeing the beginning of a mjor period of slab subduction that is fundamentally different.” Based on this discovery, Shirey and his study partner, Stephen Richardson, predict that continental drift began around 3 billion years ago (Harmon, 2011).

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Specific dates such as “3 billion years ago” can be hard to configure in geological history, and are made even more difficult since continents and seafloors are in a constant state of change because of weathering and plate tectonics. However, there are some old pieces of continents, known as cratons, which have deep mantle roots reaching about 200 kilometers below Earth’s surface. These cratons contain the diamonds used in Shirey’s study and were formed by subsurface high pressures billions of years ago and were kept protected by relatively low temperatures. In order to extract information from these diamonds to come to their conclusion, Shirey and Richardson assembled a collection of diamonds over a 3 year span and scanned them with an electron microscope. After scanning, the diamonds were sliced using a laser to extract tiny particles for analysis using a spectrometer. After particles were extracted, they were compared to radiometric dating samples to arrive at estimates of when the minerals were locked inside of the diamonds, giving them their figure of 3 billion years (Harmon, 2011).

Harmon’s article encompassing Shirey’s study provides information about how the Earth may have appeared prior to Pangaea, which began to break apart around 225 million years ago (Christopherson, 2011, p.314). While predictions are made that Pangaea was not the first or last supercontinent to exist, little is known about the Earth’s geological history or surface composition before Pangaea’s existence. Shirey and his partner aimed to answer this question, “how far can we extend the current knowledge of processes that shaped the surface of the earth (Harmon, 2011)?” Due to our recent studies of tectonic activity and makeup in class, I found the article to provide interesting facts and insight that complimented what I learned from lecture and the text about tectonic activity. Being provided with an example of how scientists are trying to predict the history of Earth’s crust allowed me to understand more thoroughly how scientists make predictions using rock history and radioactive dating as well as how important different components of plate tectonics are to Earth’s history and the future changes that our planet will experience. Since Earth has existed for 4.6 billion years, and Pangaea only represents a portion of that time, it is interesting to have a look at when processes may have began that caused the formation of Pangaea and of our continents today (Christopherson, 2011, p. 320).

Through thorough research completed by credible geologists, Katherine Harmon provided an informative article that was also an interesting read. Also, by giving the reader definitions of terms and an explanation Shirey’s study step-by-step, the article was easy to read and understand. In addition to an in-depth analysis of the study on diamonds, Harmon also gave opinions from other geologists like John Platt, who says that while 3 billion years ago may be a correct estimate for the beginning of continental drift, we cannot be sure because our planet might have different fundamentally at that point in time and we do not have enough data to form a concise opinion. Providing opinions from opposing sides give a fair analysis of the Shirey’s claim in order to not misguide the reader.

Harmon’s article provided me with supplemental knowledge that complimented what has been covered in class about plate tectonics and continental drift. By using a geological study from credible scientists, Harmon gave insight on the origin of continental drift.


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