Earth Structure and Continental Drift

Earth Structure

• Earth has three main layers: crust, mantle, core
• Crust: Lithosphere, varies in thickness, cool, mostly granite (SIAL) and basalt (SIMA) rocks, solid rocks
• Mantle: Mesosphere, 2900km thick, over 2000°C, semi-liquid (molten)
• Core: Core-baryshpere, outer ~2175km thick, about 5500°C, iron and nickel collectively called NiFe, inner core is solid due to pressure from other layers

The Crust

• Makes up continents and ocean floors

• Composed of two parts: continental (granite, sial, 35-70km thick), oceanic (basalt, sima, 6-10km thick)

• Continental crust: older, lighter, lots of granite

• Oceanic crust: younger, heavier, mostly basalt

Continental Drift Theory

• Proposed by Alfred Wegener in 1912
• Suggested that 300 million years ago all continents were one supercontinent called Pangaea
• Later split into Laurasia (northern) and Gondwanaland (southern)

Evidence supporting continental drift theory

• Matching coastlines
• Similar rock types and structures
• Similar fossils on different continents

Plate Tectonic Theory

• Earth's crust consists of plates (continental and oceanic)
• Plates are constantly in motion, moving towards each other (convergent/collision) or away from each other (divergent/spreading)
• Movement caused by convection currents in the mantle
• 10 major plates

Types of Plate Margins

• Constructive (divergent): plates move apart, mid-ocean ridges form, volcanic activity
• Destructive (convergent): plates collide, trenches and fold mountains form, associated volcanic activity
• Conservative (transform): plates slide past each other, earthquakes are common

Folding

• Bending of rocks due to plate movement (compression)
• Folds include:
  • Simple folds
  • Asymmetrical folds
  • Overfolds
  • Overthrust/thrust faults

Formation of Fold Mountains

• Continental-oceanic and continental-continental collisions (convergence)

Characteristics of Fold Mountains

• Steep slopes, great vertical heights, several peaks, valleys, parallel ranges, lakes, and ice caps
• Usually forested

Difference between old/young fold mountains

• Old fold mountains are lower and have broad peaks, gentle slopes, and shallow valleys, while young fold mountains are higher with sharp/narrow peaks, steep slopes, and deep valleys

Positive Impacts of Fold Mountains on Human Activities

• Tourism, mining, lumbering, agriculture, and pastoral farming

Other Impacts of Fold Mountains

• Windbreaks, defense, barriers to communication, cold temperatures, thin soils in steep areas

Faulting

• Fracture of earth crust due to compressional, tensional, and lateral forces
• Types of faults include:
  • Normal fault
  • Reverse fault
  • Tear fault

Formation of Rift Valleys

• Two theories: compressional and tensional forces
• Features of great rift valley: parallel faults, steep slopes, 7200km length, 30-100km width, presence of lakes and rivers.

Impacts of Rift Valleys on Human Activities

• Positive: scenic beauty, water sources for irrigation, arable farming, lumbering, mining, tourism
• Negative: soil erosion, barrier to construction

Volcanicity

• Magma, ash, and gases forced to the surface
  • Types include flowing lava, volcanic bombs, fragments of rocks, ash, and dust
  • Magma reaches the surface through a vent.

Types of Volcanoes

• Lava cones
• Composite cones
• Ash and cinder cones

Stages of Volcanoes

• Active, Dormant, Extinct

Impacts of Volcanoes

• Positive: fertile volcanic soils, scenic beauty, mineral presence, water supply, fishing, irrigation
• Negative: danger/destruction to human life during eruptions, cold temperatures, thin-soil, environmental pollution, destruction of natural vegetation and animal habitats and property losses.

Detecting Earthquakes

• Intensity: effort produced/strength of the earthquake; detected via seismograph.
• Magnitude (size): total energy produced measured on the Richter scale.

Why interiors of continents often do not experience earthquakes

• Distance from plate boundaries
• Stable plates/rigid plates.

Explore the fascinating layers of the Earth including the crust, mantle, and core. Delve into the concept of Continental Drift proposed by Alfred Wegener, which explains how continents have moved over geological time. This quiz covers the composition, thickness, and characteristics of Earth’s layers and provides insights into the evidence supporting the theory of continental drift.