What Triggers the Movement of Tectonic Plates?

It's the driving force behind the creation of mountains, volcanic eruptions, and the drifting of continents. So, what drives the movement of tectonic plates? Dive into the origins of the continental drift theory and understand how scientists unravel these geological mysteries.

Origins of Continental Drift

In 1911, German meteorologist and geophysicist Alfred Wegener was conducting research in a university library when he came across a scientific paper that described ancient fossils of the same plants and animals discovered on both sides of the Atlantic Ocean.

This discovery sparked Wegener's curiosity about how identical organisms could have evolved in two places separated by vast stretches of ocean.

Some scientists proposed that land bridges once connected these regions. However, Wegener, after examining maps of Africa and South America's coastlines, came up with a different hypothesis: what if these continents were once connected and then drifted apart, a process still occurring today?

Inspired by this idea, Wegener developed his theory of continental drift, which was initially dismissed as absurd.

By the 1950s and 1960s, however, scientists began to reconsider Wegener's ideas, coming to believe that he was onto something significant. They recognized that pieces of the Earth's crust are gradually shifting—a phenomenon that not only helps explain many of the planet's features but may also play a crucial role in making life on Earth possible.

The Theory of Plate Tectonics

The concept of plate tectonics asserts that the Earth's crust and upper mantle consist of multiple major and minor plates. These plates fit together seamlessly, yet they are constantly shifting, sometimes colliding with one another, and other times drifting apart.

Tectonic Shift

The shifting of tectonic plates, also known as plate motion or tectonic shift, has been ongoing for billions of years. A study conducted by researchers at Johns Hopkins University and published in the August 2019 edition of the journal Nature suggests that plate tectonics began around 2.5 billion years ago and has been evolving ever since.

Mantle Convection

"The Earth operates as a massive heat engine," says Ray Russo, an associate professor of geology at the University of Florida and a plate tectonics expert, in an email.

"The heat that remains from planetary formation, gravitational compression, and radioactive decay is trapped within Earth's interior. Since heat naturally flows from warmer regions to cooler ones, this heat from the interior tends to move toward the colder surface. Convection is the most efficient process for transferring this heat from the deep interior to the Earth's surface. Thus, on a large scale, hot mantle material rises and replaces cooler material formed at Earth's surface."

"The cold material in question is essentially the Earth's rigid plates," Russo elaborates. "As these plates cool, they become denser and eventually sink into the mantle, aiding in the cooling of the planet and causing mantle movements on a global scale. That is, in essence, plate tectonics."

How does the heat energy lead to the movement of entire plates? One explanation is slab pull. When dense oceanic plates sink beneath less-dense continental plates, they drag the rest of the plate with them, a phenomenon known as slab pull.

The movement of the plates occurs at an extremely slow rate — the average speed is just 0.6 inches (1.5 centimeters) annually, although scientists hold differing opinions on whether the pace of movement is accelerating or decelerating.

How Plates Move

The plates interact along their edges in three distinct ways.

Divergent Boundaries

A divergent boundary exists where two plates move away from one another, creating a zone where earthquakes are frequent and hot magma, or molten rock, rises from the mantle to the surface, forming new crust.

Convergent Boundaries

On the other hand, when two plates collide, a convergent boundary forms. The collision can cause the edges of the plates to buckle and rise, forming mountain ranges, or bend to create deep ocean trenches.

Chains of volcanoes frequently form along these boundaries. Convergent boundaries produce continental crust but also destroy crust from the ocean floor.

Transform Plate Boundaries

In a transform plate boundary, two plates slide past each other. The crust along this boundary will be cracked and broken, but unlike other types of boundaries, it does not create new crust. Earthquakes are common along these faults.

The Formation of Volcanoes

As Russo points out, plate tectonics have a profound impact on the entire planet and its natural processes. One key reason is that the movement of plates leads to the formation of volcanoes — essentially fractures in the crust that act as vents for heat and lava — and their eruptions continuously renew the ocean basins, which cover 72 percent of the Earth's surface.

Equally important, volcanic activity driven by tectonic plate movement causes lighter, less dense minerals to separate from the denser ones in the Earth's mantle. "The accumulation of these lighter minerals contributes to the formation and growth of continents, where we reside," Russo explains.

Plate Movement and the Ocean

The movement of tectonic plates has played a crucial role in creating the conditions that make life on Earth viable. It has facilitated interactions between hot volcanic rocks and ocean water, with the leaching of ions from these rocks influencing the salinity of the oceans.

"Life originated in the oceans, bathed in this ion-rich water, and humans, for instance, have blood salinity that mirrors the salinity of seawater as a direct result of this," says Russo.

Furthermore, volcanic activity triggered by tectonic movements has also contributed to the formation of fertile soils, supporting plant growth, food production, and the oxygen necessary for sustaining human life and large animals, according to Russo.

Plate Tectonics and Climate

By altering the arrangement of continents and ocean basins, plate tectonics affects the planet's climate. As Russo explains, "The current layout of ocean basins ensures the continuous movement of warm equatorial waters toward polar regions, preventing extreme temperature differences between the equator and the poles."

Mountains created by tectonic forces are also crucial carbon dioxide sinks, helping to reduce atmospheric CO2 levels by forming new minerals. This process fluctuates in response to temperature changes, allowing mountains to function as large-scale thermostats.

Plate Tectonics and Evolution

The gradual movement of the continents has also been pivotal in the process of biological evolution. As Russo clarifies, "Speciation — the emergence of new species — occurs when a single population of plants or animals is split into two isolated groups, often as a result of a supercontinent breaking apart and the formation of new ocean basins between its fragments."

This chain of events might bring a sense of validation to Alfred Wegener, who, tragically, passed away in 1930 after disappearing in a blizzard during an expedition in Greenland.