Plate tectonics is defined as gliding over of tectonic plates of earth’s crust over its semi fluid asthenosphere. This movement of plates accounts for the formation of biogeography of earth with mountains, earthquakes, volcanoes, and the distribution of continents and oceans over millions of years.
Of late tectonic plates movements and the impact on biogeography is researched with unprecedented significance. Tectonic plates and their movement have pivotal role in the evolution of species including mankind. How?
The planet earth has tectonic plates over its surface and which are in constant motion. Their movement and collisions are associated with significant transformations in earth’s geological and oceanographic structures.
What are tectonic plates?
Tectonic plates are large, fragmented sections of Earth’s upper mantle and crust that cover the entire globe.These tectonic plates are in continuous movement and the movements and collisions lead to formation of huge mountains, and ocean trenches and various other geological features. These activity of tectonic plate happens at different intervals reshaping global geography over millions of years.
The term plate tectonics is derived from Latin word tectonicus or from Ancient Greek word tektonikos meaning ‘pertaining to building’
The tectonic plates on the surface of Earth on Lithosphere have been slowly moving since 3–4 billion years ago.Earth’s lithosphere, the rigid outer shell including the crust and upper mantle, is fractured into seven or eight major plates and many minor plates or “platelets”. The relative movement of the plates typically ranges from zero to 10 cm annually.
Tectonic plates are composed of the oceanic lithosphere and the thicker continental lithosphere, each topped by its own kind of crust.
What are plate boundaries?
Plate boundaries are formed by movement of different types of tectonic plates relative to each other. Tectonic plate movement range from 10 to 40 millimetres per year (0.4 to 1.6 in/year). Where the plates meet, their relative motion determines the type of plate boundary as convergent, divergent, or transform.
Three types of plate boundaries exist, characterized by the way the plates move relative to each other.
They are associated with different types of geomorphological changes& climate change.
1.Divergent boundaries (constructive boundaries or extensional boundaries).
These are boundaries where two plates slide apart from each other. This rifting may lead to the formation of new ocean basin.
At zones of ocean-to-ocean rifting, divergent boundaries form by seafloor spreading, allowing for the formation of new ocean basin.
2.Convergent boundaries (destructive boundaries or active margins)
These boundaries occur where two plates slide toward each other. The convergent boundaries may form either a subduction zone (one plate moving underneath the other) or a continental collision.
Subduction zones :
1.ocean-to-continent subduction, where the dense oceanic lithosphere plunges beneath the less dense continent plate.
2. ocean to ocean subduction
here older denser oceanic crust slips beneath less dense ocean
associated with subduction zones, and the basins that develop along the active boundary are often called “foreland basins”.
At zones of ocean-to-ocean subduction a deep trench forms in an arc shape. The upper mantle of the subducted plate then heats and magma rises to form curving chains of volcanic islands e.g. the Aleutian Islands, the Mariana Islands, the Japanese island arc.
At zones of ocean-to-continent subduction mountain ranges form, e.g. the Andes, the Cascade Range.
Continental collision zones:
At continental collision zones two masses of continental lithospheres are converging. As they are of similar density, neither is subducted.
The plate edges are compressed, folded, and uplifted forming mountain ranges, e.g. Himalayas and Alps. Closure of ocean basins can occur at continent-to-continent boundaries.
3.Transform boundary
Transform boundaries (conservative boundaries or strike-slip boundaries) occur where plates are neither created nor destroyed. Instead, two plates slide, or precisely they grind past each other, along transform faults.
Strong earthquakes may happen along a fault. The San Andreas Fault in California is an example of a transform boundary exhibiting dextral motion.
In addition to these three boundaries other plate boundary zones occur where the effects of the interactions are not very clear.
Geomorphological consequences of tectonic plate movements
It is intriguing to understand that plate tectonics affects climate patterns, ocean currents, and the evolution of species.
The boundaries where tectonic plates interact are risky zones of increased volcanic and seismic activity. Volcanic eruptions and earthquakes are common in these zones.
Earthquakes do occur when tectonic plates slip past each other, while volcanoes form where plates collide and one dives under the other (subduction), or where plates pull apart (divergent movement).
Along convergent plate boundaries,as the process of subduction carries the edge of one plate down under the other plate and into the mantle there is reduction in the total surface area (crust) of Earth. The lost surface at one boundary is balanced by the formation of new oceanic crust along divergent margins by seafloor spreading[ divergence] and thus keeping the total surface area constant in a tectonic “conveyor belt”.
The mankind has always amazed at the formation of huge mountain ranges since time immemorial. Study of tectonic plate movements unraveled this mystery to man a few decades ago. The tectonic plates can collide with each other and the forceful collision cause the land to be forced upward, creating mountain ranges. Similarly, divergence when happens on oceanic plates it leads to formation of new ocean basin. ocean-to-ocean subduction leads to the formation of deep marine trenches typically.
Impact of plate tectonics on global climate
Over millions of years, the continents have drifted apart and have come together, creating new oceans and continents.
These movements of tectonic plates affect global climate by influencing ocean currents, which distribute heat around the planet. Mountains formed by tectonics can also affect regional climates and function as important sinks for carbon dioxide.
Impact of tectonic plate movement on evolution
The separation and collision of continents compel species to adapt to new environments created.
This can lead to new evolutionary paths or extinctions.
Impact on marine environment
The formation of new ocean ridges may happen from plate tectonics. The subsequent cooling and sinking of oceanic crust can displace seawater, causing global sea levels to rise.
Beyond earthquakes and volcanoes, plate tectonics can contribute to tsunamis and landslides.
According to a hypothesis proposed by Robert Stern and Taras Gerya, plate tectonics are a necessary criterion for a planet to be able to sustain complex life as they play a key role in regulating the carbon cycle.
Continental drift theory helps biogeographers to explain the disjunct biogeographic distribution of present-day life found on different continents.
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