Getting the Continental Drift

Getting the Continental Drift

Earthquakes and volcanos serve as important reminders of the phenomenal forces at work underneath Earth’s surface. The shape and arrangements of the continents change as the massive tectonic plates float across the more fluid upper mantle. This tectonic activity changed the initial, water-covered state of Earth, covering roughly 30% of the planet with continents. Additionally, it replaces continental landmass lost to erosion.

Every few hundred million years all the continents group together to form supercontinents such as Pangaea and Rodinia. Eventually, these supercontinents split up and start a new cycle of continental drift that eventually forms a new supercontinent.

While an abundance of geological data records the motions of the continents over time, scientists have struggled to model such behavior in the lab. However, two New York University scientists have recently built a model that demonstrates cyclic behavior analogous to the recorded continental drift. Their model includes a high-viscosity glycerin/water mixture with heavier-than-water plastic beads (which play the role of continents). The model is heated and cooled in a way reflective of processes operating inside Earth.

When the model was heated and cooled in the absence of the beads, the glycerin/water mixture flowed in a circle for long periods of time without change. Upon adding the beads, the circulation pattern reversed directions every few hours. Thus, they conclude that the continents play a critical role in the cyclic building of supercontinents. The thermal mass associated with the continents affects the flow of rock in the underlying mantle, causing it to change directions periodically. Previous thinking assumed that continents simply rode along on the flow of mantle rock.

Without the flow reversal, the supercontinent would never split apart to begin a new cycle and plate tectonics would eventually grind to a halt. While this change would eliminate earthquakes, the loss of tectonic activity would also rapidly (on geological timescales) lead to an uninhabitable Earth. This research provides scientists with another tool for exploring how well-designed Earth’s interior processes support life.