Earth's Layers and Plate Tectonics

• The Earth is divided into layers with distinct properties.

Crust

• Outermost layer with a thickness of 5–70 km.
• Made of solid rock, mainly silicate minerals.
• Divided into continental crust (thicker, less dense, mostly granite) and oceanic crust (thinner, denser, mostly basalt).
• The lithosphere includes the crust and the uppermost part of the mantle, broken into tectonic plates.

Mantle

• Approximately 2,900 km thick and contains silicate minerals rich in iron and magnesium.
• The upper mantle is solid, while the asthenosphere is semi-fluid, facilitating plate movement.
• Mantle convection, where hot material rises, cools, and sinks, drives plate tectonics.

Outer Core

• About 2,200 km thick, composed of molten iron and nickel.
• Convection currents of liquid metal generate Earth’s magnetic field.

Inner Core

• About 1,220 km thick, composed of solid iron and nickel.
• Extremely hot, around 5,000–6,000°C, but remains solid due to immense pressure.

Plate Tectonics

• Plate Tectonics explains how the Earth's lithosphere is divided into plates that move over the asthenosphere because of mantle convection.

Continental Drift

• Proposed in 1912 by Alfred Wegener.
• Continents were once part of a supercontinent called Pangaea, which broke apart.
• Fossil evidence includes similar fossils on different continents, such as Mesosaurus in South America and Africa.
• Geological evidence includes similar rock formations on distant continents.
• Climatic evidence includes coal deposits in Antarctica, suggesting a warmer past.

Seafloor Spreading

• Proposed by Harry Hess to explain new oceanic crust formation at mid-ocean ridges.
• Magma rises from the mantle at ridges, cools to form new crust.
• Older crust is pushed outward, moving plates apart.
• Older crust sinks back into the mantle at subduction zones.
• Evidence includes magnetic striping, showing Earth's past reversals.
• The age of oceanic crust is younger near mid-ocean ridges and older near trenches.

Plate Boundaries

• Divergent boundaries occur where plates move apart such as at the Mid-Atlantic Ridge.
• Convergent boundaries occur where plates collide forming mountains or subduction zones for example the Himalayas or Mariana Trench.
• Transform boundaries occur where plates slide past each other, causing earthquakes like the San Andreas Fault.

Earthquakes

• Earthquakes occur due to the release of energy from stress in the Earth's crust.

Causes of Earthquakes

• Tectonic activity involves plates moving at faults.
• Volcanic activity involves magma movement causing ground shaking.
• Human-induced activities like mining or reservoir-induced seismicity (dam failures).

Seismic Waves

• P-waves (Primary) are the fastest, travel through solids and liquids, and have compressional movement.
• S-waves (Secondary) are slower, travel only through solids, and have shear movement.
• Surface waves move along Earth's surface and are the most destructive.

Measuring Earthquakes

• The Richter Scale measures magnitude on a logarithmic scale, increasing by a factor of 10 per unit.
• The Mercalli Scale measures intensity based on observed effects.

Risk Reduction and Preparedness

• Preparation involves securing objects, having emergency kits, and conducting earthquake drills.
• During use the "drop, cover, and hold on" method, and staying away from windows.
• After, check for injuries, avoid damaged buildings, and prepare for aftershocks.

Minerals

• Minerals are naturally occurring, inorganic, solid with a definite chemical composition and crystalline structure.
• Examples of minerals include quartz, feldspar, mica, and calcite.

Properties of Minerals

• Color varies; some minerals exhibit multiple colors.
• Streak is the color of a mineral in powdered form, for example, hematite has a red streak.
• Luster is either metallic (shiny) or non-metallic (dull, glassy, pearly).
• Hardness is measured using the Mohs scale, ranging from 1 (talc) to 10 (diamond).
• Cleavage refers to smooth breaks, while fracture refers to rough breaks.

Types of Rocks

Igneous Rocks

• Formed from cooled magma or lava.
• Intrusive rocks cool slowly underground, such as granite.
• Extrusive rocks cool quickly on the surface, such as basalt.

Sedimentary Rocks

• Formed from compressed sediments.
• Clastic rocks are formed from rock fragments, such as sandstone.
• Chemical rocks are precipitated from solution, such as limestone.
• Organic rocks are formed from plant or animal remains, such as coal.

Metamorphic Rocks

• Formed from existing rocks under heat and pressure.
• Foliated rocks have layers, such as slate and schist.
• Non-foliated rocks lack layers, such as marble and quartzite.

Soil Structure and Profiling

• Soil consists of a mix of minerals, organic material, water, and air.

Soil Horizons (OAECBR)

• O-Horizon (Organic Layer) contains decomposing plant/animal material.
• A-Horizon (Topsoil) is rich in nutrients and best for plant growth.
• E-Horizon (Eluviation Layer) has minerals leached from A, leaving sand/silt.
• C-Horizon (Parent Material) contains weathered rock fragments.
• B-Horizon (Subsoil) accumulates leached minerals like iron and clay.
• R-Horizon (Bedrock) is the solid rock base.

Soil Formation Factors

• Parent Material is the type of rock weathered.
• Climate, including temperature and precipitation, affects soil formation.
• Organisms such as microbes, plants, and animals contribute organic matter.
• Topography, or slope, affects erosion and soil depth.
• Time: older soils develop more layers.