2.1 Theory of plate tectonics
11 min read•august 21, 2024
Plate tectonics shapes Earth's surface, driving continental movement and creating diverse landscapes. This theory explains how large-scale geological features form over time, directly impacting and evolution across the globe.
Understanding plate tectonics is crucial for biogeography. It reveals how landmasses have shifted, oceans formed, and mountains risen, influencing climate patterns and creating opportunities for species to diversify, migrate, or face extinction over millions of years.
Fundamentals of plate tectonics
- Plate tectonics forms the foundation for understanding Earth's dynamic surface processes and their influence on global biogeography
- This theory explains how large-scale geological features form and evolve over time, directly impacting species distribution and evolution
Earth's lithosphere structure
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- consists of the crust and uppermost mantle, ranging from 50-280 km thick
- Divided into rigid tectonic plates that float on the partially molten
- Oceanic lithosphere thinner (5-10 km) and denser than continental lithosphere (30-50 km)
- Lithospheric plates move relative to each other, driven by convection currents in the mantle
Types of tectonic plates
- Major plates cover large areas (Pacific, North American, Eurasian)
- Minor plates smaller in size (Caribbean, Scotia, Philippine)
- Oceanic plates composed primarily of basaltic rocks and denser than continental plates
- Continental plates made of lighter granitic rocks, allowing them to "float" higher on the asthenosphere
- Some plates contain both oceanic and continental crust (African, South American)
Plate boundaries and interactions
- Divergent boundaries where plates move apart (Mid-Atlantic Ridge)
- Convergent boundaries where plates collide (Andes Mountains)
- Transform boundaries where plates slide past each other (San Andreas Fault)
- Plate interactions create various geological features
- Mountains
- Oceanic trenches
- Volcanic island arcs
- Boundaries often associated with increased seismic and volcanic activity
Driving forces of plate movement
- Plate tectonics driven by complex interactions of forces within Earth's interior
- Understanding these forces crucial for predicting plate movements and their biogeographical impacts
- Plate motion influences species migration, isolation, and evolution over geological time scales
Convection currents in mantle
- Heat from Earth's core creates convection cells in the mantle
- Upwelling of hot material at divergent boundaries pushes plates apart
- Downwelling of cooler material at convergent boundaries pulls plates together
- Convection currents create a "conveyor belt" effect, driving plate motion
- Mantle plumes may also contribute to localized plate movement and hotspot volcanism (Hawaiian Islands)
Ridge push and slab pull
- Ridge push results from gravitational sliding of newly formed oceanic crust away from mid-ocean ridges
- Elevated topography at ridges creates a downslope force, pushing plates apart
- Slab pull occurs when subducting plates sink into the mantle due to their higher density
- Slab pull considered the dominant force in plate tectonics, accounting for about 80% of plate motion
- Combination of ridge push and slab pull creates a self-sustaining system of plate movement
Gravitational sliding
- Lithospheric plates slide down the gravity gradient from elevated regions to lower areas
- Contributes to the movement of plates away from mid-ocean ridges and towards subduction zones
- Influenced by variations in crustal thickness and density across plate boundaries
- Plays a role in and the breakup of supercontinents (Pangaea)
- Interacts with other forces to determine overall plate motion and velocity
Plate tectonic processes
- Plate tectonic processes shape Earth's surface and create diverse habitats for species
- These processes operate on geological timescales, influencing long-term biogeographical patterns
- Understanding these mechanisms helps explain current and past species distributions
Seafloor spreading
- Occurs at divergent boundaries, particularly mid-ocean ridges
- Magma rises from the mantle, cools, and forms new oceanic crust
- Newly formed crust moves away from the ridge, creating space for more magma to rise
- Process creates a symmetrical pattern of magnetic stripes on the seafloor
- Rate of varies between different ocean basins (fast in the Pacific, slow in the Atlantic)
Subduction zones
- Found at convergent boundaries where denser oceanic plates sink beneath less dense plates
- Oceanic crust descends into the mantle, forming deep oceanic trenches (Mariana Trench)
- Subducting plate experiences increasing pressure and temperature as it descends
- Partial melting of the subducting plate generates magma, leading to volcanic arc formation
- Island arcs (Japan)
- Continental volcanic arcs (Andes Mountains)
- Subduction zones play a crucial role in recycling Earth's crust and driving plate tectonics
Continental drift vs plate tectonics
- Continental drift proposed by in 1912, based on the fit of continents and fossil evidence
- Plate tectonics developed in the 1960s, providing a mechanism for continental movement
- Key differences:
- Continental drift focused solely on continent movement, while plate tectonics explains movement of both oceanic and continental crust
- Plate tectonics provides a comprehensive explanation for Earth's geological processes, including mountain building and earthquake activity
- Plate tectonics incorporates continental drift as part of a larger, more complex system of global crustal movement
Evidence supporting plate tectonics
- Multiple lines of evidence from various scientific disciplines support the theory of plate tectonics
- This evidence provides a robust framework for understanding Earth's geological history and its impact on biogeography
- Integrating different types of evidence allows for a comprehensive understanding of plate tectonic processes
Fossil distribution patterns
- Similar fossil organisms found on different continents support past continental connections
- Mesosaurus fossils in South America and Africa indicate these continents were once joined
- Glossopteris flora found across southern continents supports the existence of Gondwana supercontinent
- Fossil evidence helps reconstruct past continental configurations and migration routes for species
- Biogeographical analysis of fossil distributions contributes to understanding of plate tectonic history
Paleomagnetism and seafloor stripes
- Earth's magnetic field periodically reverses polarity, recorded in magnetic minerals in rocks
- Seafloor rocks show symmetrical patterns of magnetic stripes parallel to mid-ocean ridges
- Stripes represent alternating periods of normal and reversed magnetic polarity
- Pattern and width of stripes used to determine seafloor spreading rates and ages
- Paleomagnetism in continental rocks helps reconstruct past latitude positions of continents
Fit of continental margins
- Jigsaw-like fit of continental margins, particularly between South America and Africa
- Fit improves when considering the continental shelf rather than just the coastline
- Geological features match across separated continents (mountain ranges, rock types)
- Bathymetric data reveals submarine features that support continental connections
- Computer models demonstrate how continents can be reassembled into past supercontinents (Pangaea, Rodinia)
Tectonic plate movement rates
- Plate movement rates vary significantly across different plate boundaries and over geological time
- Understanding these rates crucial for reconstructing past continental configurations and predicting future changes
- Plate velocities directly impact the pace of geological processes and biogeographical changes
Measurement techniques
- GPS (Global Positioning System) provides high-precision measurements of current plate motions
- Satellite laser ranging uses orbiting reflectors to measure distances between points on Earth's surface
- VLBI (Very Long Baseline Interferometry) uses radio telescopes to measure plate movement relative to distant quasars
- Seafloor magnetic anomalies used to calculate past plate movement rates
- Geological features (offset river valleys, fault systems) provide evidence of long-term plate motion
Variations in plate velocities
- Plate velocities range from less than 1 cm/year to over 15 cm/year
- Fastest moving plates include the Pacific Plate (~8-10 cm/year)
- Slowest moving plates typically found in plate interiors (North American Plate ~1-2 cm/year)
- Velocity affected by factors such as:
- Plate size and composition
- Length of subducting slab
- Presence of mantle plumes
- Plates can rotate, resulting in different velocities at different points on the plate
Historical plate movements
- Plate movements have varied significantly over geological time
- Supercontinents form and break apart in cycles (Wilson Cycle)
- Pangaea began breaking up ~200 million years ago, leading to current continental configuration
- India's northward movement at ~15-20 cm/year resulted in rapid Himalayan mountain formation
- Atlantic Ocean opening began ~180 million years ago and continues today at ~2-4 cm/year
- Pacific Ocean shrinking due to subduction around its margins
Impact on global geography
- Plate tectonics fundamentally shapes Earth's surface features and landscapes
- These processes create diverse habitats and environmental conditions, influencing species distribution
- Understanding tectonic impacts on geography essential for interpreting biogeographical patterns
Mountain formation processes
- Collision of continental plates creates fold mountains (Himalayas, Alps)
- Subduction of oceanic plates under continental plates forms volcanic mountain ranges (Andes, Cascades)
- Rifting and extension can create fault-block mountains (Basin and Range Province)
- Mountain formation alters regional climates and creates barriers to species migration
- Orogenesis (mountain building) influences erosion rates and sediment distribution
Ocean basin evolution
- Seafloor spreading at mid-ocean ridges creates new oceanic crust
- Subduction at convergent boundaries destroys old oceanic crust
- Ocean basins open, expand, and close over geological time (Atlantic opening, Pacific shrinking)
- Basin evolution affects ocean currents, climate patterns, and marine species distribution
- Bathymetric features (mid-ocean ridges, trenches) create diverse marine habitats
Continental fragmentation and assembly
- Supercontinents break apart due to rifting and seafloor spreading
- Smaller continental fragments (terranes) can accrete onto larger landmasses
- Continental collisions form new landmasses and mountain ranges
- Fragmentation and assembly cycles influence:
- Global climate patterns
- Sea level changes
- Species migration and isolation events
- Current configuration of continents result of long-term fragmentation and assembly processes
Plate tectonics and biogeography
- Plate tectonics plays a crucial role in shaping global biodiversity patterns
- Tectonic processes create and modify habitats, influencing species distribution and evolution
- Understanding plate tectonic history essential for interpreting current biogeographical patterns
Vicariance vs dispersal
- Vicariance occurs when populations are separated by geological events (continental breakup)
- Dispersal involves species moving across barriers to colonize new areas
- Plate tectonics can create both vicariance events and dispersal opportunities
- Vicariance explains similar species on different continents (marsupials in Australia and South America)
- Dispersal important for island biogeography and long-distance colonization events
Allopatric speciation
- Occurs when populations become geographically isolated
- Plate tectonic processes can create physical barriers leading to isolation
- Isolated populations may evolve independently, potentially forming new species
- Examples of allopatric speciation driven by tectonics:
- Galapagos finches
- Madagascar's unique fauna
- Understanding past tectonic events helps explain current species distributions and evolutionary relationships
Biodiversity hotspots and tectonics
- Many biodiversity hotspots associated with tectonically active regions
- Plate boundaries often create diverse landscapes and environmental gradients
- Mountain building processes increase habitat diversity and promote speciation
- Examples of tectonic-influenced biodiversity hotspots:
- Tropical Andes
- Mediterranean Basin
- California Floristic Province
- Tectonic activity can both create and destroy habitats, influencing long-term biodiversity patterns
Major tectonic events
- Significant tectonic events throughout Earth's history have profoundly impacted global biogeography
- These events create opportunities for species diversification, migration, and extinction
- Understanding major tectonic events crucial for interpreting current and past species distributions
Pangaea breakup
- Began ~200 million years ago during the Triassic period
- Initial rifting separated Laurasia (northern continents) from Gondwana (southern continents)
- Breakup occurred in stages, with different continents separating at different times
- Created new ocean basins (Atlantic, Indian) and altered global climate patterns
- Pangaea breakup led to:
- Increased biodiversity through isolation and adaptation
- Development of unique flora and fauna on different continents
- Long-term changes in global climate and ocean circulation
Formation of current continents
- North America separated from Eurasia ~60-65 million years ago
- India collided with Asia ~50 million years ago, forming the Himalayas
- Australia separated from Antarctica ~35 million years ago
- Formation of the Isthmus of Panama ~3 million years ago connected North and South America
- These events resulted in:
- Isolation of certain species groups (Australian marsupials)
- Creation of new migration routes (Great American Biotic Interchange)
- Development of new climatic zones and habitats
Future tectonic predictions
- Atlantic Ocean expected to continue widening for millions of years
- Mediterranean Sea likely to close as Africa collides with Europe
- Australia projected to move northward, potentially colliding with Southeast Asia
- Formation of a new supercontinent (Pangaea Ultima) predicted in ~250 million years
- Potential impacts on future biogeography:
- Creation of new mountain ranges and biodiversity hotspots
- Alteration of global climate patterns
- Changes in ocean circulation and marine ecosystems
Plate tectonics and climate
- Plate tectonic processes significantly influence global and regional climate patterns
- Changes in continental configurations and topography affect atmospheric and oceanic circulation
- Understanding tectonic-climate interactions crucial for interpreting past and present biogeographical patterns
Oceanic circulation patterns
- Plate tectonics alters the size, shape, and connectivity of ocean basins
- Changes in ocean circulation affect heat distribution and global climate patterns
- Opening and closing of oceanic gateways impact thermohaline circulation
- Panama Isthmus closure strengthened Gulf Stream
- Drake Passage opening led to Antarctic Circumpolar Current formation
- Ocean currents influence nutrient distribution and marine productivity
- Changes in oceanic circulation can lead to regional climate shifts and impact species distributions
Mountain range effects
- Orogenesis (mountain building) creates rain shadow effects and alters regional climates
- Mountain ranges act as barriers to atmospheric circulation and moisture transport
- Uplift of the Tibetan Plateau intensified the Asian monsoon system
- Andes Mountains create distinct climate zones along western South America
- Mountain formation can lead to:
- Increased regional biodiversity through habitat diversification
- Creation of isolated ecosystems and endemic species
- Alterations in precipitation patterns and river systems
Continental position influence
- Distribution of landmasses affects global heat distribution and climate patterns
- Polar continents (Antarctica) can lead to ice sheet formation and global cooling
- Equatorial land bridges can disrupt ocean circulation and heat transport
- Continental configurations influence:
- Monsoon systems and precipitation patterns
- Formation and intensity of ocean currents
- Global temperature gradients and climate zones
- Past continental positions explain historical climate events (Cretaceous warm period, Pleistocene ice ages)
Tectonic hazards
- Plate tectonic processes create various natural hazards that impact ecosystems and human societies
- Understanding these hazards crucial for predicting and mitigating their effects on biogeography
- Tectonic events can cause rapid changes in habitats and species distributions
Earthquakes and fault lines
- Occur due to sudden release of energy along fault lines between tectonic plates
- Most common at plate boundaries, particularly transform and convergent boundaries
- Magnitude measured on Richter scale, ranging from micro-earthquakes to mega-thrust events
- Earthquakes can cause:
- Ground rupture and displacement
- Landslides and soil liquefaction
- Tsunamis in coastal and marine environments
- Ecological impacts include habitat destruction and creation of new colonization opportunities
Volcanic activity at plate boundaries
- Most volcanoes occur at convergent and divergent plate boundaries
- Subduction zones produce explosive stratovolcanoes (Mount Fuji, Mount Vesuvius)
- Mid-ocean ridges feature effusive basaltic eruptions
- Hotspot volcanism occurs within plates, often creating island chains (Hawaii)
- Volcanic activity impacts ecosystems through:
- Ash fall and lava flows destroying habitats
- Creation of new land and substrates for colonization
- Release of gases and particulates affecting global climate
Tsunami formation and propagation
- Generated by sudden displacement of water, often due to undersea earthquakes
- Can also be caused by landslides, volcanic eruptions, or meteorite impacts
- Tsunamis travel at high speeds in deep water, slowing and increasing in height near shore
- Impacts on coastal ecosystems include:
- Erosion and sedimentation of shorelines
- Saltwater intrusion into freshwater habitats
- Destruction and recolonization of coastal vegetation
- Tsunami events can lead to long-term changes in coastal biogeography and species composition
Key Terms to Review (18)
Alfred Wegener: Alfred Wegener was a German meteorologist and geophysicist who is best known for proposing the theory of continental drift in the early 20th century. His ideas laid the groundwork for understanding the formation and breakup of supercontinents like Pangaea, influencing later developments in the theory of plate tectonics, including how plates interact at boundaries and how ancient biogeographical patterns emerged as a result of these processes.
Asthenosphere: The asthenosphere is a semi-fluid layer of the Earth's mantle located beneath the lithosphere, characterized by its ability to flow slowly over time. This layer plays a crucial role in the movement of tectonic plates, as it provides a malleable foundation that allows the rigid lithospheric plates to glide and interact with one another. The asthenosphere's properties are key to understanding the dynamics of plate tectonics and the various interactions at plate boundaries.
Biogeographical barrier: A biogeographical barrier is a physical feature that prevents or restricts the movement of species, leading to isolation and divergence in populations over time. These barriers can be natural, such as mountains, rivers, and oceans, or man-made, like highways and urban developments. They play a critical role in shaping the distribution of organisms and influencing evolutionary processes by limiting gene flow between populations.
Continental drift: Continental drift is the theory that the Earth's continents have moved over geological time, shifting positions relative to one another. This movement is primarily due to the processes associated with plate tectonics, leading to significant changes in climate, sea levels, and the distribution of species across the globe.
Divergent boundary: A divergent boundary is a tectonic plate boundary where two plates move away from each other, leading to the creation of new oceanic crust as magma rises to the surface. This process occurs primarily along mid-ocean ridges, where seafloor spreading takes place, and can also be found in continental rift zones. Divergent boundaries are crucial for understanding how the Earth's lithosphere is recycled and reshaped over time.
Earthquake generation: Earthquake generation refers to the process by which stress builds up in the Earth's crust and is eventually released in the form of seismic waves, resulting in an earthquake. This phenomenon is closely tied to the movement of tectonic plates, where the interactions at plate boundaries create the conditions for stress accumulation. As tectonic plates shift, they can become locked due to friction, leading to a gradual build-up of energy that, once released, manifests as an earthquake.
Harry Hess: Harry Hess was a prominent American geologist known for his work in the mid-20th century that significantly advanced our understanding of plate tectonics and oceanography. He proposed the theory of seafloor spreading, which provided a mechanism for continental drift, and laid the groundwork for the modern theory of plate tectonics by explaining how new oceanic crust is formed at mid-ocean ridges and pushes older crust away. His research also helped to establish the concept of plate boundaries and interactions.
Himalayan Orogeny: The Himalayan Orogeny refers to the mountain-building event that led to the formation of the Himalayas, which began around 50 million years ago and continues to shape the region today. This orogeny is primarily a result of the collision between the Indian Plate and the Eurasian Plate, resulting in significant geological changes and diverse ecosystems across the area. The ongoing tectonic activity has also created a variety of landscapes and influenced climate patterns in South Asia.
Isostasy: Isostasy refers to the gravitational equilibrium between Earth's crust and the denser underlying mantle. This concept explains how the crust 'floats' on the mantle, adjusting its height and density in response to changes in surface loads, like ice sheets or mountain ranges. Isostasy is crucial for understanding the stability of landforms and the processes that shape Earth's surface over geological time.
Lithosphere: The lithosphere is the rigid outer layer of the Earth, comprising the crust and the uppermost part of the mantle. This layer plays a crucial role in the movement of tectonic plates, which are large sections of the lithosphere that float on the semi-fluid asthenosphere beneath. The interactions between these plates lead to geological phenomena such as earthquakes, volcanic activity, and mountain formation.
Mantle convection: Mantle convection is the slow, churning motion of Earth's mantle caused by heat from the core that leads to the movement of tectonic plates on the surface. This process is crucial for understanding how heat and material circulate within the Earth, driving the dynamics of plate tectonics, influencing continental drift, and shaping interactions at plate boundaries.
Mid-ocean ridge: A mid-ocean ridge is an underwater mountain range formed by tectonic plates diverging and new oceanic crust being created through volcanic activity. These ridges are significant features of the ocean floor, serving as sites of seafloor spreading where magma rises to create new crust and drive the movement of tectonic plates, connecting to larger geological processes and plate interactions.
Ring of Fire: The Ring of Fire is a horseshoe-shaped area in the Pacific Ocean basin known for its high levels of seismic activity, including earthquakes and volcanic eruptions. This region is a direct result of tectonic plate movements, where numerous plates interact along their boundaries, leading to the formation of various geological features such as volcanic arcs and oceanic trenches.
Seafloor Spreading: Seafloor spreading is the geological process through which new oceanic crust is formed at mid-ocean ridges and slowly moves away from the ridge, driven by tectonic forces. This phenomenon provides crucial evidence for the theory of plate tectonics and explains how continents can drift over geological time, reshaping Earth's surface.
Species distribution: Species distribution refers to the natural range and arrangement of different species across geographical areas. It encompasses the patterns and processes that determine where species are found, how abundant they are in those locations, and the environmental factors that influence their presence. Understanding species distribution is crucial because it connects ecological dynamics, evolutionary processes, and biogeographic patterns shaped by various factors, including tectonic movements, climate conditions, and regional biodiversity.
Subduction Zone: A subduction zone is a region of the Earth's crust where one tectonic plate moves under another, causing the denser oceanic plate to sink into the mantle beneath a lighter continental plate or another oceanic plate. This process leads to significant geological activity, including earthquakes, volcanic eruptions, and the formation of mountain ranges, making subduction zones crucial components of the theory of plate tectonics.
Transform Boundary: A transform boundary is a type of tectonic plate boundary where two plates slide past each other horizontally. This movement creates significant geological features and can lead to earthquakes, as the friction between the sliding plates can cause stress to build up until it's released suddenly. Transform boundaries are essential for understanding how tectonic plates interact and shape the Earth's surface.
Volcano: A volcano is an opening in the Earth's crust where molten rock, gases, and ash can escape from beneath the surface. These geological structures play a crucial role in shaping landscapes and are primarily formed at tectonic plate boundaries or over hotspots, contributing to various geological phenomena and the distribution of biomes across the globe.