Plate Tectonic Theory

Plate Tectonic Theory

• Describes the lithosphere's large-scale motion and its fragmentation into tectonic plates
• Tectonic plates constantly move and interact at their boundaries

Significance

• Explains the distribution of continents and oceans
• Contributes to the formation of mountains, volcanoes, and earthquakes
• Plays a role in the creation and destruction of Earth's crust
• Influences the distribution of mineral resources
• Shapes the evolution of landscapes and ecosystems over geological time

Key Concepts

• Lithosphere comprises the crust and uppermost mantle, averaging 100 km (60 miles) thick
• Tectonic Plates consist of irregularly shaped slabs of solid rock
• Asthenosphere is a semi-molten layer beneath the lithosphere
• Plate Boundaries denote zones of significant geological activity where tectonic plates interact

Driving Force

• Convection in Earth's mantle is the primary force behind plate tectonics and the circulation of hot, less dense material with cooler, denser material

Ridge Push

• Gravity causes elevated lithosphere at mid-ocean ridges to slide down, pushing plates apart

Slab Pull

• At subduction zones, denser oceanic lithosphere sinks, pulling the plate along and is considered the strongest driving force

Divergent Boundaries

• Plates move apart, magma fills the gap, creating new oceanic crust
• Features include Mid-Atlantic Ridge, rift valleys such as the East African Rift System, and volcanic activity

Transform Boundaries

• Plates slide horizontally past each other
• Crust is neither created nor destroyed
• Features include fault zones and frequent earthquakes, like the San Andreas Fault in California

Convergent Boundaries

• Tectonic plates collide, potentially leading to subduction or deformation, forming mountains and geological features

Types of Collisions

• Oceanic-Oceanic involves one plate subducting, creating deep-sea trenches and volcanic island arcs like Japan and the Philippines
• Oceanic-Continental sees the denser oceanic plate subducting, forming deep-sea trenches and mountain ranges like the Andes
• Continental-Continental occurs when two plates collide, crumpling and folding to form mountain ranges such as the Himalayas

Earth's Layers

• Crust is the outermost, rigid layer divided into thinner, denser oceanic crust (basalt) and thicker, less dense continental crust (granite)
• Mantle is the thickest layer beneath the crust, mostly solid but with a partially molten asthenosphere, rich in iron and magnesium silicates
• Outer Core is a liquid layer of iron and nickel, generating Earth's magnetic field
• Inner Core is a solid sphere of iron and nickel, kept solid by immense pressure

Evidence Supporting Plate Tectonics

• Fit of Continents like South America and Africa
• Fossil Evidence of similar species across separated continents
• Rock Type and Structural Similarities across joined continents
• Paleoclimate Evidence indicates past climates and continental movement
• Seafloor Spreading including mid-ocean ridges and magnetic patterns
• Earthquake and Volcano Distribution concentrated along plate boundaries
• GPS Measurements showing current tectonic plate movement

Electromagnetic Spectrum: Radio Waves

• These possess low frequency and energy
• They can travel extensively and penetrate various obstacles
• They are easily generated through oscillating electric charges (antennas)
• Uses: AM/FM radio, TV, mobile, satellite communication, Wi-Fi, Bluetooth, GPS
• High-intensity generate heat, while long-term exposure effects are under investigation
• Potential environmental impact from antenna arrays on wildlife

Microwaves

• Higher frequency and energy than radio waves
• They aree absorbed by water, fats, and sugars
• Can transmit through the atmosphere, but are affected by moisture
• Used in satellite communication, radar, microwave ovens, and mobile networks
• Primary hazard is thermal effects, with potential non-thermal effects under investigation
• Can interfere with sensitive electronic equipment

Infrared (IR) Radiation

• Have higher frequency and energy than microwaves
• Objects emit IR based on temperature
• Some IR wavelengths are absorbed by the atmosphere, contributing to the greenhouse effect
• Used for heating, thermal imaging, remote controls, and short-range communication
• High-intensity exposure causes burns
• Certain wavelengths absorbed by greenhouse gases contribute to global warming

Visible Light

• The portion of the EM spectrum detectable to the human eye
• Different wavelengths manifest as different colors
• Can be refracted, reflected, and absorbed
• Allows us to see, and used in photography, optics, illumination, communication, medicine, energy, and agriculture

Ultraviolet (UV) Radiation

• Has a higher frequency and energy than visible light
• Classified into UVA, UVB, and UVC, it can cause chemical reactions in materials
• Most UV radiation is absorbed by the Earth's ozone layer
• Used for sterilization, medical treatments, industrial processes, security, and astronomy
• UVB and some UVA cause DNA damage, aging, and increase cancer risk
• Stimulates vitamin D production
• Ozone depletion increases the amount of harmful UV, and UV can degrade materials

X-Rays

• They have high frequency and energy
• They penetrate soft tissues but are absorbed by denser materials
• Ionizing radiation removes electrons from atoms
• Application in medical imaging, cancer therapy, security, and astronomy
• Can damage DNA and increase cancer risk
• Carefully controlled to minimize adverse effects

Gamma Rays

• Possess extremely high frequency and energy
• Are highly penetrating and cause ionizing radiation
• Produced by nuclear reactions and radioactive decay
• Used for cancer therapy, medical imaging, sterilization, industrial processes, and astronomy
• Can cause significant damage to DNA and cells
• Hazardous in nuclear accidents or improper handling of radioactive materials

Light

• Form of electromagnetic radiation visible to the human eye, exhibiting wave-particle duality
• Travels in straight lines (rays)
• Its vacuum speed is approximately 299,792,458 meters per second
• It slows down in transparent materials

Reflection

• It is the bouncing of light off a surface
• Specular Reflection occus onr smooth, polished surfaces (mirrors) and creates a clear image
• Diffuse Reflection occusr on rough surfaces forming no clear image

Law of Reflection

• Includes the incident ray, reflected ray, and normal which lie in the same plane
• The Angle of Incidence is equal to the Angle of Reflection

Refraction

• It is the bending of light passing from one medium to another with different optical density
• Light slows and bends towards the normal as it enters a denser medium
• Light speeds up and bends away entering a less dense medium

Key Terms

• The Incident ray strikes the boundary between two media
• The Refracted Ray passes through the boundary and bent
• Normal is an imaginary line perpendicular at the point of incidence
• Angles of Incidence and Refraction describes a relationship between incident and refracted rays

Snell's Law

• This describes the relationship between angles of incidence, refraction, and refractive indices: n₁ sin(∠i) = n₂ sin(∠r)

Applications

• Lenses focus or diverge light to form images
• Prisms disperse white light into its spectrum
• Optical fibers use total internal reflection for data transmission
• Mirages and apparent depth are caused by refraction through layers of air with different temperatures and densities

Image Formation in Mirrors and Lenses

• Real images are inverted
• Real image are located between the center of curvature and the focal point, smaller than the object
• Magnification is less than 1