EARTH SCI Q2 ROCKS HEAT EARTH

Earth’s Internal Heat Source

Crust
- The outermost layer, approximately 5–70 km thick, divided into two types: continental crust (thicker and less dense) and oceanic crust (thinner and denser).
- Broken into tectonic plates that float on the mantle, these plates constantly move, driven by the heat from below.
Mantle
- Extends down to about 2,890 km; composed of very hot, dense rock that flows slowly over geological time.
- This layer is responsible for the movement of tectonic plates through convection currents formed by heat from the Earth's core.
Outer Core
- A liquid layer composed mainly of molten nickel and iron, about 2,250 km thick.
- This motion of molten metal creates the Earth's magnetic field, which plays a crucial role in protecting the planet from solar radiation.
Inner Core
- A solid sphere due to the extreme pressure that overcomes temperature, with temperatures reaching up to 9,000°F (5,000°C).
- Composed primarily of iron and nickel, it is believed to rotate at a slightly different rate than the rest of the Earth, contributing to the magnetic field.

Primordial Heat
- Heat remaining from the Earth’s formation (4.6 billion years ago), generated from the kinetic energy of colliding particles during accretion.
- This heat is gradually transported towards the surface through convective and conductive processes, influencing geological activity.
Frictional Heating
- Generated by the movement of denser materials sinking towards the Earth’s center, creating heat through friction as these materials interact under pressure.
- This process is vital for driving plate tectonics, which in turn affects earthquake and volcanic activity.
Radioactive Decay
- The decay of heavy isotopes such as Potassium-40, Uranium-235, Uranium-238, and Thorium-232 significantly contributes to the Earth's internal heat.
- The energy released from these decays generates substantial heat, which impacts mantle dynamics and geothermal gradients.

Magma forms under specific conditions deep within the crust or upper mantle, primarily due to:
- Increase in temperature: Attributed to depth and proximity to molten rock.
- Decrease in pressure: Occurring when rock ascends towards the surface, which can trigger melting.
- Addition of water: Water lowers the melting point of rocks, facilitating magma creation.

Decompression Melting
- Occurs when rock ascends towards the surface, reducing pressure and allowing the material to melt.
Flux Melting
- Involves the introduction of volatiles (such as water) into hot rock, which lowers its melting point, enabling magma production.

Intrusion
- Magma can move into the crust without erupting at the surface, leading to the growth of a volcano from the inside as it cools and solidifies.
Extrusion
- When magma erupts at the surface, it is called lava, which can lead to the formation of volcanoes, with different characteristics depending on the composition of the magma.

Subduction Zone: Occurs when oceanic crust collides with continental crust, resulting in melting facilitated by heat from descending plates and the release of fluids from subducted materials.
Hot-Spot Volcanism: Involves magma forming from localized heat sources within the mantle, enabling it to rise through the lithosphere, forming volcanic islands like those in Hawaii.
Rift Zones: Characterized by tectonic plates pulling apart, which allows magma to reach the surface through fissures, leading to volcanic activity, seen in places like the East African Rift.

Metamorphism is the geological process that alters rocks in form and composition due to intense heat and pressure without melting.

Temperature: Ranges typically from 350-850°C, induced by burial depth or contact with magma.
Pressure: Varies in tectonic settings, influencing the type and extent of metamorphic changes.

Regional Metamorphism
- Occurs over large areas, typically associated with mountain building (orogeny) under high pressure and temperature conditions.
Contact Metamorphism
- Happens when surrounding rocks are heated by intruding magma, leading to localized changes.
Shock Metamorphism
- Caused by impact events such as meteor strikes, generating extreme conditions over short periods.
Burial Metamorphism
- Low-grade metamorphism occurring due to the pressures and temperatures associated with layers of sedimentary material being buried.

Deformation is the process where stress or heat forces impact rocks, altering their shape, size, or volume.

Tensional Stress: Rocks are pulled apart, typically at divergent boundaries.
Compressional Stress: Rocks are pushed together, common at convergent boundaries.
Shear Stress: Rocks slip past each other, characteristic of transform boundaries.

Elastic Deformation: Temporary changes in shape that return to the original form post-stress.
Ductile Deformation: Permanent changes without fracturing occur when rocks are subjected to significant heat and pressure.

Faults are categorized into three types based on the movement of rock during deformation:
- Normal Faults: Result from tensional forces.
- Reverse Faults: Form under compressional forces.
- Strike-Slip Faults: Occur from shear stress, where rocks slide past each other.

The Philippine Fault Zone (PFZ) is a prominent strike-slip fault with significant earthquake risk.
The West Valley Fault (WVF) produces major earthquakes that can be devastating, with recorded events up to a magnitude of 7.2.