What causes continental drift? The intriguing geological process of continental drift has fascinated geologists for generations.
It is fascinating to see how it alters Earth’s surface gradually over millions of years. You may have seen examples of this phenomenon in the real world.
But, the question is, “What caused continental drift in the first place?”
Plate tectonics, which moves Earth’s lithosphere, drives continental drift, as they meet, pull apart, and slide past each other on the semi-fluid asthenosphere.
What Causes Continental Drift?
Our planet’s geology, temperature, and species distribution have all been shaped in significant ways by continental drift, the steady shifting of the continents through time.
German scientist Alfred Wegener proposed the concept of continental drift in 1912.
Wegener hypothesized that the continents had previously formed a single landmass known as Pangaea before slowly migrating apart.
It was not until the 1960s that the theory of plate tectonics was developed, allowing scientists to better grasp the causes behind continental drift.
More about Earth’s Lithosphere and Tectonic Plates
The lithosphere includes the crust and the highest part of the mantle and is Earth’s outermost shell.
The thickness of this stiff layer ranges from roughly 5 kilometres in marine regions to about 200 kilometres on land.
Large and small tectonic plates make up the lithosphere and “float” atop the more malleable asthenosphere, which is part of the upper mantle and is formed of partially molten rock.
An Important Consideration
The two main types of tectonic plates are oceanic and continental.
As magma cools and solidifies at mid-ocean ridges to generate basaltic rocks, continental plates feature a wider range of rock types, from granitic to sedimentary.
Fact: The Juan de Fuca Plate covers an area of only a few hundred thousand square kilometers, whereas the Pacific Plate spans over 100 million square kilometers.
The Connection between Plate Tectonics and Continental Drift
As the theory of plate tectonics provides the mechanism responsible for the movement of continents over time, it is impossible to separate the two concepts.
This connection can only be grasped by first familiarizing yourself with the fundamentals of both plate tectonics and continental drift.
The Hypothesis of Continental Drift
The hypothesis proposes that throughout millions of years, the Earth’s continents have moved with respect to one another.
According to the idea of plate tectonics, the lithosphere, the rigid outer layer of Earth, is cracked into a succession of tectonic plates ranging in size from relatively small to relatively enormous.
Earthquakes, volcanic eruptions, and the uplift of mountain ranges are only some of the geological events that can be attributed to the shifting of these tectonic plates.
Because the continents themselves are made up of bigger tectonic plates, plate tectonics and continental drift are intrinsically linked.
What Contributes to Plate Tectonics and Continental Drift?
The continents vary their positions relative to one another over geologic time because the plates that support them are constantly moving.
Many forces are contributing to the overall process of plate tectonics or continental drift, such as:
- Mantle convection
- Ridge push
- Slab pull
Mantle Convection: The Engine Beneath the Surface
The mantle is a critical layer of Earth because it influences the surface and drives the motion of tectonic plates.
To learn more about it, you have to examine the mantle’s:
- Makeup
- Architecture
- Internal processes
The Earth consists of the crust, the mantle, the outer core, and the inner core.
The mantle is the intermediate layer between the crust and the core, and it extends from a surface depth of about 35 km (below the oceanic crust) to a depth of about 2,900 km.
An Important Thing to Know
There are two distinct layers of the mantle, the upper and the lower. From the crust’s underside to a depth of roughly 660 km is the upper mantle.
And from that depth to the core-mantle boundary lies the lower mantle.
Temperature, pressure, and mineral composition all play a role in setting apart these two zones.
Fact: The mantle is formed mostly of solid, ultramafic rock abundant in iron and magnesium silicates and accounts for around 84% of Earth's total volume.
The Mantle Convection and Its Role in Plate Movements
Mantle convection is a critical phenomenon deep within the Earth’s mantle and drives tectonic plate motion.
The movement of the plates is affected by the transmission of heat within the mantle, which causes a circulation of material and the production of forces.
The Role of Pressure and Temperature
Temperature and pressure gradients in the Earth’s mantle cause convection.
There are two main drivers of heat production:
- Radioactive decay
- Retained heat
Because of the increased temperature, the mantle material gradually loses density and rises to the surface.
Loss of heat to the cooler surroundings causes the hot material to contract, grow denser, and sink back into the mantle as it nears the top.
Convection currents in the mantle are generated by this periodic process of rising and sinking.
The Movement of Tectonic Plates
The motion of tectonic plates is driven in large part by these convection currents.
The base of the plates is pulled along by the currents as they rise and expand horizontally beneath the lithosphere.
This force, in addition to others like ridge push and slab pull, is what actually gets the plates moving.
More about the Ridge Push and Continental Drift
An important geophysical mechanism that aids in the motion of tectonic plates and the phenomenon of continental drift is ridge push, also known as gravitational sliding.
New oceanic crust is developed as a result of volcanic activity near mid-ocean ridges, where forces are generated.
The tectonic plates are pushed apart by the gravitational force created as the freshly produced crust moves away from the ridge and cools.
Divergent plate borders, such as those between two tectonic plates that are moving apart, give rise to underwater mountain ranges known as mid-ocean ridges.
Similarly, magma from the Earth’s mantle rises via these crevices and fissures, eventually cooling to form a new oceanic crust.
This ongoing process of magma upwelling and solidifying causes the seabed to spread and the ocean basins to enlarge.
What Contributes to the Continental Drift?
Mid-ocean ridges are where new crust is formed; as this happens, the older crust retreats from the ridge axis and cools.
By contracting and becoming denser as it cools, the crust grows thicker and sinks into the less dense asthenosphere below.
Due to the topographic slope created by this impact, a downslope force is exerted on the tectonic plate as it moves from the higher ridge crest to the deeper ocean basin.
By producing a horizontal force that propels the movement of tectonic plates, ridge push aids in continental drift.
Continents that are part of these plates gradually move over time, which causes land masses to drift with respect to one another.
Fact: The plates are set in motion, away from the mid-ocean ridges, by a horizontal force and other phenomena such as mantle convection and slab pull.
Slab Pull and Its Role in Continental Drift
Slab pull, the force generated by the oceanic plate sinking, is a major factor in driving plate movement and strongly affects the motion of the Earth’s lithosphere.
At a subduction zone, a denser oceanic plate slides beneath a less dense plate, usually a continental plate, and sinks into the mantle.
The subduction of one tectonic plate beneath another is a defining feature of subduction zones, which are found along convergent plate borders.
Here, the denser oceanic plate sinks under the continental plate, which is less dense.
The oceanic plate undergoes partial melting when it subducts and interacts with the Earth’s mantle.
The development of magma as a result of this interaction can result in volcanic activity in the overlying plate.
How Does It Contribute to Continental Drift?
The subducting oceanic plate produces a sinking or pulling force as it sinks into the mantle, and this is where slab pull comes into play in plate movement.
Because of its mass, the rest of the plate is dragged down toward the dense, colder slab.
The entire oceanic plate is pushed in the direction of the subduction zone by this downward force.
Fact: Geological phenomena including earthquakes, volcanic eruptions, and mountain formation are all caused by the tectonic plates moving as a result of these pressures.
Takeaway
What causes continental drift? Plate tectonics is the long geological process that alters Earth’s surface and is what drives continental drift.
Its motion is driven mostly by mantle convection, ridge push, and slab pull. All of these factors combine to cause continental drift.
