Earth's Layers: Chemical and Mechanical

• Science relies on observation and experimentation to systematically understand the natural world
• Science seeks to build knowledge through testing hypotheses and theories

Layers of the Earth

• Earth consists of multiple layers
• These layers are categorized by chemical composition and mechanical properties

Chemical Layers

• Crust: The Earth’s solid outermost layer, is divided into continental and oceanic types
• Continental crust exhibits greater thickness and lower density compared to oceanic crust
• Mantle: A predominantly solid layer extending approximately 2,900 km deep
• The mantle composes the majority of Earth's volume
• Silicate rocks rich in iron and magnesium are the primary components
• Core: The Earth’s innermost layer with a liquid outer core and a solid inner core
• Outer core: Liquid iron and nickel predominate
• Inner core: Solid iron and nickel exist due to immense pressure

Mechanical Layers

• Lithosphere: A rigid outer layer that includes the crust and a portion of the upper mantle
• The lithosphere is divided into tectonic plates
• Asthenosphere: A partially molten, ductile layer beneath the lithosphere in the mantle
• Lithospheric movement is facilitated by the asthenosphere
• Mesosphere: A stronger and more rigid section of the mantle below the asthenosphere
• Outer core: A liquid layer responsible for Earth’s magnetic field
• Inner core: A solid and dense sphere

Types of Plate Boundaries

• Plate boundaries mark the meeting points of two tectonic plates
• Three primary types exist
• Divergent
• Convergent
• Transform

Divergent Boundaries

• Two plates move away from each other
• Magma rises from the mantle to fill the gap, forming new crust
• Typically found at mid-ocean ridges
• Example: The Mid-Atlantic Ridge
• Rift valleys can form on continents
• Example: The East African Rift Valley
• Volcanic activity and shallow earthquakes are characteristic

Convergent Boundaries

• Two plates move toward each other
• The outcome depends on the types of plates involved
• Oceanic-Continental Convergence:
• The denser oceanic plate subducts beneath the continental plate
• This forms oceanic trenches, volcanic arcs, and mountain ranges
• Example: The Andes Mountains along the western coast of South America
• Intense volcanic and seismic activity are typical
• Oceanic-Oceanic Convergence:
• One oceanic plate subducts beneath another
• This process leads to the creation of oceanic trenches and volcanic island arcs
• Example: The Mariana Islands in the western Pacific Ocean
• Strong earthquakes and volcanic eruptions often occur
• Continental-Continental Convergence:
• Two continental plates collide
• Neither plate subducts significantly due to similar buoyancy
• Large mountain ranges form as a result
• Example: The Himalayan Mountains, resulting from the collision of the Indian and Eurasian plates
• Characterized by intense folding, faulting, and seismic activity

Transform Boundaries

• Two plates slide past each other horizontally
• Crust is neither created nor destroyed
• Commonly found on the ocean floor, offsetting mid-ocean ridges
• Can also occur on continents
• Example: The San Andreas Fault in California
• Frequent earthquakes are common

Movements of the Earth

• Various processes shape Earth's surface and cause geological events
• Plate tectonics and internal heat drive these movements

Plate Tectonics

• The lithosphere is divided into plates that move relative to each other
• Convection currents in the mantle drive this movement
• Plate movement causes events such as
• Earthquakes
• Volcanoes
• Mountain building

Convection Currents

• The primary driving force behind plate tectonics
• Hotter, less dense material rises from the Earth's core and mantle
• Cooler, denser material sinks
• Circular flow in the asthenosphere drags the lithospheric plates

Types of Plate Movements

• Divergence: Plates move apart at mid-ocean ridges and rift valleys
• This result in seafloor spreading and new crust formation
• Convergence: Plates collide at subduction zones or continental collision zones
• This results in crust destruction, mountain formation, and volcanoes
• Transform Motion: Plates slide past each other horizontally along transform faults
• This results in earthquakes as stress is released

Earthquakes

• Occur from sudden energy releases in the lithosphere that create seismic waves
• Most occur along plate boundaries
• Earthquakes are caused by rupture and displacement of rocks along a fault

Seismic Waves

• Energy waves travel through the Earth
• Generated by earthquakes, volcanic eruptions, and explosions
• Types of seismic waves include:
• P-waves: Primary waves, compressional, travel through solids and liquids
• S-waves: Secondary waves, shear, travel only through solids
• Surface waves: Travel along the Earth’s surface, causing the most damage

Volcanoes

• Geological features where magma erupts onto the surface
• Often found at convergent and divergent plate boundaries
• Also occur at hotspots, caused by plumes of hot mantle material rising to the surface
• Example: The Hawaiian Islands
• Eruptions vary from effusive lava flows to explosive ash and gas eruptions