By Clare Sherman —
The National Parks talk series hosted an event on Tuesday, September 23rd, to discuss the geological processes that have shaped the Earth in its current state. The Zoom event, presented by Dr. Tammie L. Gerke from 4:30 to 6:30, included topics such as the history of plate tectonic theory, the different types of plate boundaries, a guided look at the Earth’s surface through geological time, and the predicted future movement of Earth’s surface.
Dr. Gerke began with the idea that plate tectonics is a recently accepted and still developing theory, honing in on two individuals whose research most heavily contributed to our modern understanding of these processes. The Continental Drift Theory was proposed around 1917 and suggested simply that Earth’s continents had at some point moved apart. Meteorologist Alfred Wegener supported this theory by examining evidence related to continental shapes, paleontological data, and mountain chains. The evidence from continental shapes was described as puzzle pieces. On a map, South America and Africa look like puzzle pieces that could fit together. Wegener’s paleontological data included nearly identical land-dwelling fossils found on differing continents, while his mountain chain evidence similarly described mountains with related structures and rocks existing on separate continents. Regardless of how many lines of evidence Wegener presented to the scientific community, he could not determine a plausible explanation for the mechanisms that moved these continents. Plate tectonics remained a mystery until the late 20th century.
Crediting Harry Hess with the more developed plate tectonic theory, Dr. Gerke explained that World War II provided the evidence needed to understand the process behind continental movement. Lost war submarines led to the mapping of the ocean floor, and evidence from paleomagnetic data, seafloor sediments, and mantle plumes ultimately revealed that convection currents in Earth’s mantle drive seafloor spreading, which in turn pushes tectonic plates apart.
Having laid the foundation for the development of plate tectonic theory, Dr. Gerke thoroughly clarified the different types of plate boundaries responsible for shaping Earth’s surface and creating volcanoes, mountains, and earthquakes.
Divergent boundaries are commonly present on the ocean floor, where plates move apart to create crust through the formation of mid-oceanic ridges. A subtype of divergent boundaries, continental rifting occurs when plates diverge on land. This creates rift valleys that can eventually evolve into ocean basins. Convergent boundaries are defined by plates colliding, effectively recycling crust back into Earth’s mantle. There are three distinct types of convergent boundaries: oceanic-continental convergent boundaries, which create volcanic arcs through the melting of oceanic crust; oceanic-oceanic convergent boundaries, which create a type of volcanic arc on oceanic crust called a volcanic island arc; and continental-continental convergent boundaries, which create mountain ranges through the piling up of materials, or obduction. The third type, transform boundaries, occurs when plates slide past one another, connecting divergent boundaries or creating powerful earthquakes.
After viewers reviewed the basics of plate boundary types, Dr. Gerke then presented several maps illustrating plate movement through geological time, starting with the Rodinia supercontinent, which began forming between 2.1 and 1.8 billion years ago. She then worked through the landmass’s gradual breakup and into the creation of the Pangea supercontinent, which eventually formed the continents that exist today.
The event concluded with compelling projections of Earth’s future surface movement. In the next 50 million years, gradual plate movement will create drastic geological changes, such as the collision of Australia and Asia and the closing of the Mediterranean and Red Sea. After 250 million years of plate movement, the supercontinent of Pangea is predicted to reform, with the Pacific Ocean widening to encircle half of Earth.
The National Parks Talk Series holds an informational meeting once a month, educating participants on geology-related topics. Readers who are interested in joining Dr. Gerke for future events can do so on Tuesday, October 21st, at 4:30 p.m. to learn about the formation of the Great Lakes, or on Tuesday, November 18th, at 4:30 p.m., to discuss the novel The Death and Life of the Great Lakes by Dan Egan, though reading is not required. Please visit the Harvey-Gardner Library Events Calendar to learn more about event details.