Earth Structure and Composition Quiz

Earth Structure

• The Earth’s structure comprises various spherical layers, categorized by chemical/elemental composition and mechanical/physical properties.

Compositional (Chemical) Layers of Earth

• Layers are defined based on their chemical or elemental makeup.

Crust

• Composed of elements like oxygen, silicon, aluminum, iron, calcium, sodium, potassium and magnesium
• 3 to 5 miles thick under the ocean, 25 miles thick under continents.

Types of Crust

• Oceanic Crust (Basaltic)
  • Formed from magma that erupts on the seafloor creating basalt lava flows or cools deeper to form igneous rock gabbro.
  • Covered by sediments, thicker near the shore.
• Continental Crust (Granitic)
  • Made up of various types of rocks.
  • Average composition is granite, less dense than oceanic crust.
  • Thicker part of the crust.

Mantle

• Layer beneath the crust, comprises 82% of the Earth’s volume.
• About 1,800 miles deep.
• Mostly made of silicate rocks rich in magnesium and iron.
• Heat causes rocks to rise.

Conduction

• Heat transfer through rapid collisions of atoms, happening in solids.
• Heat flows from warmer to cooler areas until they reach the same temperature.

Convection

• Process of material capable of movement and flow that develops convection currents.

Core

• The Earth's center, made of 85% iron metal and 15% nickel.

Plate Tectonics

• Scientific theory explaining the large-scale motion of seven major plates and numerous smaller plates.
• Began 3.3 to 3.5 billion years ago.
• Average tectonic plate thickness in the lithosphere is about 100 km.

7 Major Tectonic Plates:

• Pacific Plate (103,300,000 sq km)
• North American Plate (75,900,000 sq km)
• Eurasian Plate (67,800,000 sq km)
• African Plate (61,300,000 sq km)
• Antarctic Plate (60,900,000 sq km)
• Indo-Australian Plate (58,900,000 sq km)
• South American Plate (43,600,000 sq km)

Types of Tectonic Plates:

• Oceanic Plates: Composed of oceanic crust, mostly magnesium and silicon minerals.
• Continental Plates: Composed of continental crust, mainly aluminum and silicon materials.

Boundaries of Tectonic Plates

• Transform Boundary: Plates move past each other by sliding. Minimal damage occurs. Called faults.
• Divergent Boundary: Plates slide apart, moving in opposite directions. Often occurs in seafloors, creating new ocean floor. Volcanic activity produces mid-ocean ridges and small earthquakes.
• Convergent Boundary: Plates move against each other, one plate going underneath the other. Volcanoes and mountains are formed at these boundaries.

Movement of Tectonic Plates

• Mantle convection drives plate tectonics:
  • Hot mantle rises at the ridge axis, creating new ocean crust.
  • Top of the convection cell moves horizontally away from the ridge crest as does the new seafloor.
  • Outer limbs of the convection cells plunge into deeper mantle, dragging oceanic crust at deep-sea trenches.
  • Material sinks to the core and moves horizontally.
  • Material heats up and rises again.

Landforms and Earth Processes

• Dynamic actions within or on the Earth's surface.
• Constructive Processes: Build up earth material or landforms (e.g., erosion, transportation of sediments).
• Destructive Processes: Break down Earth material or destroy landforms (e.g., decomposition).
• Decomposition: Process of breaking down mineral constituents to form new components due to chemical action of physical agents.
• Denudation: Earth’s surface is worn away by chemical and mechanical actions of physical agents, exposing lower layers.

Processes of Weathering

• Physical Weathering: Physical breakdown of rock masses under the attack of atmospheric agents.
  • Rocks are broken into smaller irregular fragments and particles.
  • Most active in cold, dry, and higher areas.
  • Caused by temperature variations.
• Exfoliation: Curved plates of rock are stripped (onion-skin weathering).
  • Forms dome-shaped hills or dome rocks.
  • Occurs along planes of parting called joints.
  • Caused by unequal expansion and contraction due to temperature variations.
• Freeze-Thaw Weathering: Water enters rock cracks, freezes, expands, and melts, repeating until the rock splits.
• Chemical Weathering: Chemical decomposition of rock, altering mineral structure by adding or removing elements through chemical reactions between the atmosphere and rocks.
  • Occurs with water dissolving active gases from the atmosphere.
• Spheroidal Weathering: Chemical weathering caused by water penetration at joints/fractures, attacking from all sides. Concentric or spherical shells of decayed rock are loosened and separated.

Earth Process by Wind

• Erosion: Wearing away of rock along the coastline caused by destructive waves.
  • Deflation: Wind removing loose material from flat, dry areas (deserts, dry lake beds, floodplains, glacial washout plains).
  • Abrasion: Scraping of rock surfaces by friction between rocks and moving particles.
• Transportation: Wind carries sediments:
  • Bed Load: Larger and heavier particles moved by wind, not lifted higher than 30-60 cm above the surface.
  • Suspended Load: Finer particles lifted by wind hundreds of meters above the surface.
• Deposition: Wind-blown sediments are dropped and deposited forming Aeolian deposits.
  • Sand Dunes: Huge heaps of sand formed by wind deposition in recognizable shapes.
  • Barchans (Crescent-Shape Dunes): Triangular in section.
    • Steep side faces the wind.
    • Gentle side lies on the windward side.
  • Transverse Dunes: Similar to Barchans, but longer axis lies transverse to the prevailing wind direction.
  • Longitudinal Dunes: Elongated sand ridges with the longer axis parallel to the prevailing wind direction.
• Aquifuge: Neither porous nor permeable geological formation. No interconnected openings. Cannot transmit or absorb water. Suitable for groundwater occurrence.

Earthquake

• Sudden shaking of the ground caused by seismic waves passing through the Earth's rocks, most often along geologic faults.
• Release of sudden and extreme energy caused by shifting in the Earth's crust.

Seismology

• The study of earthquakes and seismic waves.

Faults

• Narrow zones where rock masses move in relation to each other.
• A planar or gently curved fracture in the Earth's crust, where compression or tensional forces cause relative displacement of rocks on opposite sides.

Classification of Faults:

• Normal Slip Fault: Crust is pulled apart. The hanging-wall block moves down relative to the footwall block.
• Reverse Slip Fault: Crust is compressed. The hanging-wall block moves up and over the footwall block.
• Strike Slip Fault: Crustal blocks move sideways past each other, usually along nearly-vertical faults.
  • Sinistral Strike Slip: Far side moves to the left.
  • Dextral Strike Slip: Far side moves to the right.

Earthquake Terminology:

• Focus: The exact spot beneath the Earth's surface where an earthquake originates.
• Epicenter: Point on the Earth's surface directly above the earthquake's focus.
• Intensity: Severity of earthquake shaking, based on its effects on people, the environment, and the Earth's surface. Determined by total energy released.
• Magnitude: Quantitative measure of the earthquake's size at its source. Based on total energy released.
  • Modified Mercalli Intensity Scale: Measures earthquake intensity based on observational effects.
  • Richter Magnitude Scale: Measures earthquake energy released using a seismograph, assigns values between 1 and 10.