Plate Tectonics and Continent Formation

Theory of Plate Tectonics and the Formation of Continents

• Plate tectonics proposes that Earth's outer layer consists of large and small plates that float and move on a more flexible layer called the asthenosphere

Theories Behind Plate Tectonics

• Raisin Theory: James Dwight Dana proposed Earth cooled and contracted like a grape turning into a raisin shape after the Big Bang
• Isostasy Theory: Clarence Edward Dutton describes isostasy as the gravitational equilibrium where Earth's crust "floats" on the denser mantle below
• Tectonic Plates Theory: Earth's outer layer is divided into different sizes of solid plates called lithospheric or tectonic plates which fit together like a jigsaw puzzle and move at rates of less than 1 to 15 cm per year

Tectonics Origin

• The Greek word "Tekton" means carpenter or builder
• Tectonic plates or lithospheric plates are massive, irregular slabs of solid rock

Theatrum Orbis Terrarum

• Abraham Ortelius noted the similarities between the coastlines of Africa, Europe, and America, suggesting that they were once connected

Continental Drift Theory

• Alfred Wegener (1915) suggested continents were once part of a single supercontinent named Pangaea
• Pangaea later broke apart into two smaller supercontinents, Laurasia and Gondwanaland.

Major Tectonic Plates

• African Plate
• South American Plate
• Indo-Australian Plate
• Antarctic Plate
• North American Plate
• Pacific Plate
• Eurasian Plate
• Nazca Plate

Earth's Mechanism of Plate Tectonics

• Modern Techniques: Scientists use various geodetic techniques, such as Satellite Laser Ranging (SLR) and the Global Positioning System (GPS)
• Seismic Tomography involves inverting seismological data to create a three-dimensional image of anomalies in seismic wave velocities within the Earth's interior
• Mantle Convection Theory: Arthur Holmes in 1929 suggests that the mantle becomes heated, its density decreases and eventually rises up
• When the mantle material cooled, it would sink exhibiting a circling behavior that he described like a conveyor belt.
• Slab Pull Theory suggests gravity and the plates themselves are responsible through the subduction process

Evidence of Plate Movement

• Lystrosaurus ("shovel reptile"): A herbivore of approximately one meter in length, dominant on land during the early Triassic period (250 million years ago)
• Lystrosaurus lacked the swimming capability to traverse oceans, suggesting these landmasses were once joined.
• Cynognathus ("dog jaw"): A mammal-like reptile of similar size to a modern wolf, lived during the Triassic period (250 million years ago)
• Cynognathus was a land-dwelling species and could not have migrated across the Atlantic Ocean
• Mesosaurus: A reptile similar to modern crocodiles, living during the early Permian period (286 to 258 million years ago)
• Mesosaurus was a coastal animal and could not have crossed the vast Atlantic Ocean
• Glossopteris: A large genus of woody, seed-bearing trees with tongue-shaped leaves, dominant during the early Permian period (299 million years ago)
• The widespread distribution of Glossopteris supports the idea of connected landmasses
• Evidence from Glaciation: Glacial deposits in regions at different latitudes suggests that these continents were once closer to the poles
• Paleoclimatology supports the theory of plate tectonics and examines the Earth's climate over geologic time scales
• Evidence from Structure and Rock Type: Coastlines and rock formations provide further evidence of plate movement, noting that the coastlines of continents, particularly Africa and South America, fit together like puzzle pieces

Plate Boundaries

• Seafloor Spreading Theory: Harry Hess' hypothesis, coined by Robert S. Dietz stating that the seafloor was formed by mid-ocean ridges that spread in both directions
• Magnetic Reversal: The process by which the North pole transforms into a South pole and vice versa

Types of Lithospheres

• Lithosphere has 2 kinds that forms different types of land/sea forms when colliding: Oceanic and Continental lithosphere
• Two continental lithospheres colliding form mountains and mountain ranges
• When two oceanic lithospheres collide forms subduction zones and chains of volcanic islands known as island arcs
• Oceanic lithosphere colliding with a continental lithosphere results in deep ocean trenches

Boundaries

• Convergent Boundary (Colliding): Also known as the destructive boundary, occurs when two plates collide
• Divergent Boundary (Spreading): Also known as the constructive boundary. Occurs when two plates move apart. Marked by mid-ocean ridges
• Transform Fault (Lateral): Also known as the conservative boundary, occurs when lithospheric plates slide past each other and where the crust is neither destroyed nor formed.
• Triple Junction is the point where the boundaries of three tectonic plates meet. At the triple junction each of the three boundaries will be one of three types a ridge, a transform, or a fault

The Internal Structure of Earth

• Rheology is the branch of physics that studies the flow of liquid matter and solid material deformation

Earth's Layers

• Lithosphere: The planet's outer layer, including the crust and upper mantle, where the thinnest layer called CRUST is found
• Asthenosphere: A highly viscous, hotter, and ductile region of the upper mantle involved in plate tectonic movement
• This is also where the lithosphere 'sits' and 'floats."
• Mantle: About 80% of the planet's mass is concentrated here, where the earth's internal heat is located and where the volcanoes' magma chamber is found
• Outer Core: Can be thought of as a ball of extremely liquid hot metals, composed of iron, nickel, and around 10% sulfur and oxygen
• Temperature is 5,000°C, so it remains liquid
• Inner Core: Has a temperature higher than the sun's surface, contrary to the outer core, inner core is solid
• The Temperature of 5,000 to 6,000 Celsius moves in a rotational pattern and believed to be the source of the Earth's magnetic field (Dynamo effect)
• Geomagnetic Field: Protects us from the harmful rays emitted by the sun
• Solar Flares: Cosmic ray event can temporarily affect field communication systems, hasten ozone layer depletion, and generate aurora phenomenon

Landforms and Processes

• Landforms are natural physical features formed by natural forces such as water, wind, ice, and tectonic plates
• Aeolian Landforms are derived from the Greek god of the wind, Aeolus, created by wind's chemical and mechanical action, in wind-dominated areas such as dunes, loess, and mushroom rocks
• Dunes are mounds or small hills made up of sand
• Loess is silt-sized, created by the accumulation of windblown dust
• Mushroom rocks are formed from earthquakes or glacial action and known as rock pedestal
• Erosional Landforms are created exclusively from erosional and weathering activities such as mesas, buttes, and canyons
• Mesas (table mountains) are elevated areas of land with flat top and steep cliffs
• Butte is similar to mesa, but covers a smaller area
• Canyons are a deep ravine between cliffs, carved from the landscape by a river, wind, or glacier
• Mountainous Landforms rise higher than the rest of their surroundings, examples are hills, volcanoes, valley or dale
• Glacial Landforms result from the actions of glaciers which are huge, slow-moving bodies of ice
• Fluvial Landforms that went sedimentation, erosion, or deposition on the river bed
• Coastal Landforms Shaped by wave refraction over thousands of years
• Delta: A low-lying triangular area at river mouths, rich in soil deposited by water
• Peninsula: A landmass bordered by water on three sides and connected to the mainland
• Meander: A bend in a river formed by erosion on the outer banks
• Sea Cliffs: High rocky coasts that plunge to the edge of the sea as results of erosional actions
• Plains: Flat and broad land areas without great changes in elevation
• Plateaus: Elevated flat-topped landforms formed by geologic uplifts, volcanic eruptions, or weathering, covering about 45% of Earth's land surface
• Mountain Ranges are large, elevated landforms with steep sides and peaks, formed by tectonic forces or volcanism through orogenesis
• The Himalayas (highest) is the highest and youngest mountain range called "House of Snow"
• Andes (longest) is considered the longest mountain chain
• The Appalachian (oldest) is the primary mountain system of the eastern part of northern America

The Dynamic Earth

• Volcanoes: A rupture in the crust of a planetary-mass object, allowing hot lava, volcanic ash, and gases to escape from a magma chamber below the surface
• Volcanism is the process and phenomena associated with the superficial discharge of molten rocks and other materials into the Earths surface
• Earthquakes: A natural phenomenon by the sudden, violent shifting of massive plates underneath Earth's surface
• Wave energy: Forms of wave energy transmitted through bedrock
• Hypocenter (Focus): The point within Earth along the geological faults where the earthquake originates
• Shallow Focus: The focus is near the surface from 0-70 km
• Deep Focus: Produced if focus is intermediate, between 70-700 km
• Epicenter: The point on the Earth's surface directly above the focus
• Fault: A crack across which the rock has been offset
• Fault Plane: The area where the fault occurs
• Fault Trace: A line that may or may not be visible
• Hanging Wall: The block of crust above the fault
• Foot Wall: The block of crust below the fault

Classification of Faults

• Normal Fault: The hanging wall moves down relative to the footwall due to extension
• Reverse Fault: (Thrust Fault) The hanging wall moves up relative to the footwall
• Strike-Slip Fault: Two blocks of crust slide past each other horizontally

Seismic Waves

• P Waves (Primary Waves): Sounds heard from the ground during earthquakes
• S Waves (Secondary Waves): Travel at 2.5 - 4 km/s and can only travel through solid materials
• Surface Waves: Arrive after P and S waves and confined to the outer layer of Earth
• Love Waves: Cause the most damage to buildings and other structures
• Rayleigh Waves: (Ground roll) Cause rock particles to move multiple ways

Electromagnetic Waves

• Electromagnetic Wave: An electrical and magnetic disturbance that moves through space at the speed of light
• Transverse Waves: The oscillating electric and magnetic fields that are perpendicular to the direction of wave propagation
• Oscillation: Represents the regular change in strength and direction of the wave
• Electromagnetic Waves do not require a medium to travel, hence they can travel to a vacuum
• Transverse Waves: Compared to water waves
• EM waves are arranged based on their frequency (f), wavelength (λ), and photon energy (E)
• Frequency: How many times the waves go up and down in one second and is measured in hertz (Hz)

Electromagnetic Spectrum

• Electromagnetic Spectrum is the full range of all possible frequencies of EM waves, from very low to very high
• Radio Waves: Have the longest wavelengths and lowest frequencies, used to broadcast radio and television
• Microwaves: Have shorter wavelengths and higher frequencies, used in cooking, radar, telephone, and other signals
• Infrared Waves: Emitted by anything that can produce heat.
• Visible Light: Makes things visible
• Ultraviolet Light: Emitted by the sun, too much exposure can sunburn
• X-Rays: Used in medical imaging
• Gamma Rays: Used to target and destroy cancerous cells in radiation therapy