🌾World Biogeography Unit 2 – Plate Tectonics: Earth's Moving Continents

What's the Big Deal?

• Plate tectonics revolutionized our understanding of Earth's dynamic surface and interior processes
• Provides a unifying framework for explaining the distribution of landmasses, oceans, earthquakes, volcanoes, and mountain ranges
• Helps us understand the interconnectedness of Earth's systems (lithosphere, hydrosphere, atmosphere, and biosphere)
• Offers insights into the evolution and distribution of life on Earth over geological timescales
• Enables us to better assess and mitigate risks associated with natural hazards (earthquakes, volcanic eruptions, and tsunamis)
• Plays a crucial role in shaping the Earth's surface and creating diverse landscapes and habitats
• Influences the global carbon cycle and climate by regulating the exchange of carbon dioxide between the Earth's interior and atmosphere

Earth's Building Blocks

• Earth is composed of three main layers: crust, mantle, and core
  • Crust is the thin, outermost layer (oceanic crust ~7 km thick, continental crust ~35 km thick)
  • Mantle is the thick, middle layer (~2,900 km thick) composed of hot, dense rock
  • Core is the innermost layer, consisting of a liquid outer core and a solid inner core
• Lithosphere is the rigid outer layer of the Earth, comprising the crust and uppermost mantle
• Asthenosphere is the partially molten, ductile layer of the upper mantle beneath the lithosphere
• Tectonic plates are large, irregularly shaped slabs of lithosphere that move relative to one another
• Plate boundaries are where two or more plates meet and interact (divergent, convergent, and transform boundaries)
• Convection currents in the mantle drive plate motion, as hot material rises and cool material sinks

Puzzle Pieces: Continental Drift Theory

• Continental drift theory, proposed by Alfred Wegener in 1912, suggested that continents were once joined together in a supercontinent called Pangaea
• Wegener observed that continents fit together like puzzle pieces (South America and Africa) and shared similar geological features and fossil records
• Evidence supporting continental drift included:
  • Matching rock formations and mountain ranges across continents (Appalachian Mountains and Scottish Highlands)
  • Identical plant and animal fossils found on different continents (Glossopteris fern)
  • Glacial deposits and striations in regions that are now in warm climates (India and Australia)
• Wegener's theory was initially rejected due to lack of a plausible mechanism for continental movement
• Plate tectonics later provided the missing mechanism and validated many of Wegener's ideas

Plate Tectonics 101

• Plate tectonics is the scientific theory that describes the large-scale motion and behavior of Earth's lithospheric plates
• Plates move at rates of a few centimeters per year, driven by convection currents in the mantle
• Three main types of plate boundaries:
  • Divergent boundaries where plates move apart and new oceanic crust is formed (mid-ocean ridges)
  • Convergent boundaries where plates collide, resulting in subduction, mountain building, and volcanism
  • Transform boundaries where plates slide past each other, causing earthquakes (San Andreas Fault)
• Hotspots are stationary mantle plumes that create volcanic chains as plates move over them (Hawaiian Islands)
• Plate tectonics explains the formation and distribution of Earth's major surface features (oceans, continents, mountains, and rift valleys)
• The theory unifies concepts from various Earth science disciplines (geology, geophysics, and oceanography)

When Plates Collide

• Convergent plate boundaries are where two plates collide, leading to subduction, mountain building, and volcanism
• Three main types of convergent boundaries:
  • Oceanic-continental convergence: dense oceanic plate subducts beneath the less dense continental plate, creating a subduction zone, volcanic arc, and accretionary wedge (Andes Mountains)
  • Oceanic-oceanic convergence: one oceanic plate subducts beneath another, forming a deep ocean trench and volcanic island arc (Mariana Trench and Islands)
  • Continental-continental convergence: two continental plates collide, resulting in the formation of high mountain ranges and plateaus (Himalayas and Tibetan Plateau)
• Subduction zones are where oceanic lithosphere descends into the mantle, causing earthquakes, volcanism, and metamorphism
• Volcanic arcs form parallel to subduction zones due to the melting of the subducting plate and the overlying mantle wedge (Cascade Range)
• Accretionary wedges are accumulations of sediment and rock scraped off the subducting plate and added to the overriding plate

Shaping Our World

• Plate tectonics plays a crucial role in shaping Earth's surface features and landscapes
• Mid-ocean ridges are underwater mountain ranges formed by divergent plate boundaries, where new oceanic crust is created (East Pacific Rise)
• Rift valleys are elongated depressions formed by the stretching and thinning of continental crust (East African Rift Valley)
• Subduction zones create deep ocean trenches, volcanic arcs, and mountain ranges along convergent plate boundaries (Peru-Chile Trench and Andes Mountains)
• Transform faults produce linear valleys and offset landforms as plates slide past each other (San Andreas Fault and Gulf of California)
• Hotspot volcanism creates volcanic islands, seamounts, and plateaus as plates move over stationary mantle plumes (Hawaiian Islands and Ontong Java Plateau)
• Plate tectonics influences the distribution of natural resources (mineral deposits, geothermal energy, and hydrocarbons)
• The interaction between plate tectonics and Earth's surface processes (erosion, deposition, and climate) creates diverse landscapes and habitats

Life on the Move

• Plate tectonics has a profound impact on the evolution and distribution of life on Earth
• Continental drift has facilitated the dispersal and isolation of species over geological timescales
• The formation and breakup of supercontinents (Pangaea, Gondwana) have influenced global climate patterns and species distribution
• Tectonic uplift and mountain building create new habitats and barriers to species dispersal (Isthmus of Panama)
• Rift valleys and subduction zones can act as biogeographic barriers, promoting speciation and endemism (East African Rift Valley and Galápagos Islands)
• Volcanic islands formed by hotspot volcanism serve as stepping stones for species dispersal and provide opportunities for adaptive radiation (Hawaiian honeycreepers)
• Plate tectonics influences ocean circulation patterns and nutrient distribution, affecting marine biodiversity and productivity
• The long-term effects of plate tectonics on climate and sea level have driven evolutionary adaptations and extinctions

Why Should We Care?

• Understanding plate tectonics is crucial for assessing and mitigating risks associated with natural hazards
• Earthquakes occur primarily along plate boundaries, and understanding their mechanisms can help in developing early warning systems and building codes (San Francisco Bay Area)
• Volcanic eruptions are closely linked to plate tectonic processes, and monitoring volcanic activity can help in evacuation planning and risk assessment (Mount Vesuvius)
• Tsunamis are often generated by large earthquakes at subduction zones, and understanding their propagation can aid in the development of warning systems and coastal protection measures (2011 Tōhoku earthquake and tsunami)
• Plate tectonics influences the distribution of natural resources (mineral deposits, geothermal energy, and hydrocarbons), which has economic and geopolitical implications
• The study of plate tectonics helps us understand the long-term evolution of Earth's climate and its impact on life
• Plate tectonic processes play a role in the global carbon cycle by regulating the exchange of carbon dioxide between the Earth's interior and atmosphere, which has implications for climate change
• Knowledge of plate tectonics is essential for making informed decisions about land use planning, infrastructure development, and resource management in tectonically active regions