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Questions and Answers

Which type of weathering involves a chemical change in the rock?

Physical Weathering

Chemical Weathering (correct)

Mechanical Weathering

Erosion

Thermal expansion is a form of chemical weathering.

False

What is the result of carbonation in chemical weathering?

Dissolving of minerals due to weak carbonic acid

The process by which rocks break down into smaller pieces without chemical change is known as _______.

Physical Weathering Signup and view all the answers

Match the weathering processes with their descriptions:

Frost Action = Breakdown due to freezing and expansion of water Hydration = Water combines with minerals Oxidation = Rusting of metallic elements like iron Abrasion = Rocks colliding against each other Signup and view all the answers

Which of the following is NOT a factor that affects the rate of weathering?

Soil Density Signup and view all the answers

Quartz is resistant to chemical weathering.

True Signup and view all the answers

What is radiogenic heat and its source?

Thermal energy from spontaneous nuclear disintegration of radioactive elements Signup and view all the answers

What is the primary agent of metamorphism?

Heat Signup and view all the answers

Is magma created by the melting of rocks due to high pressure alone?

False Signup and view all the answers

Name one process that leads to the formation of magma.

Partial melting Signup and view all the answers

The process of change in form at high temperature and pressure is known as __________.

metamorphism Signup and view all the answers

Match the following terms with their definitions:

Magma = Molten rock beneath the Earth's surface Protolith = The original, unmetamorphosed rock Foliated rock = Rock with visible crystal alignments Non-foliated rock = Rock without visible crystal alignments Signup and view all the answers

Which of the following conditions contributes to the formation of magma?

Addition of volatile substances Signup and view all the answers

High-grade metamorphism results in non-foliated rocks.

False Signup and view all the answers

What type of metamorphism occurs over large areas under high temperature and pressure?

Regional metamorphism Signup and view all the answers

The solidification of magma produces __________ rocks.

igneous Signup and view all the answers

Which of these is a characteristic of low-grade metamorphism?

Non-foliated appearance Signup and view all the answers

Study Notes

Weathering

Process by which rocks are broken down into smaller pieces.
Physical (Mechanical) Weathering involves the breakdown of rocks without any chemical change.
- Frost Action/Wedging, Freeze-Thaw Cycle: Expansion of freezing water within cracks of rocks, causing them to break apart.
- Thermal Expansion: Repeated heating and cooling of rocks causes expansion and contraction, leading to cracks and eventual breakage.
- Exfoliation: Peeling away of outer layers of rock due to unloading (reduced pressure) or fluctuations in temperature.
- Abrasion: Rocks collide and bump against each other, causing wear and tear. Agents of abrasion include wind, liquid water, solid water (ice), and gravity.
- Biological:
  - Plants expand and fracture rocks as their roots grow (Root Action).
  - Lichen and moss secrete acids that chemically break down rocks.
  - Animals, like earthworms, burrow in soil, contributing to weathering.
Chemical Weathering involves a chemical change in the rock.
- Hydration: Water combines with minerals, altering their composition. Example: Feldspar turning into Clay
- Carbonation: Water containing carbonic acid (a weak acid) dissolves minerals like calcite. Example: Formation of stalagmites (ground) and stalactites (ceiling)
- Man Made Acids: Industrial processes release nitric and sulfuric acid, leading to the chemical weathering of structures.
- Oxidation: Oxygen is added to other elements, resulting in the formation of oxides. Example: Magnetite rusting into hematite. Oxidation is common in metallic elements and ores, like Iron (Fe).

Rates of Weathering

Climate: Weathering is faster in warmer temperatures and in the presence of water.
Rock Type: Some rocks, like Quartz, are resistant to chemical weathering.

Earth's Internal Heat

Different Theories:
- Big Bang Theory: The universe began from a single point (singularity), expanding and cooling. Hydrogen and Helium are the primary elements responsible for its formation.
- Stellar Theory: Stars are fundamental building blocks of the universe.
- Super Nova Nucleosynthesis: The explosion of massive stars generates heavier elements.
- Big Crunch Theory: The universe will eventually stop expanding, begin to shrink, and become hotter.
Sources of Heat:
- Primordial Heat: Dissipation of heat during Earth's initial formation (first few million years). This includes Accretion/Accretional Energy (heat generated during the initial formation of the Earth).
- Radiogenic Heat: Thermal energy released from the spontaneous nuclear disintegration of radioactive elements within Earth. Example: Uranium (U) and Thorium (Th)
  - Isotopes: Atoms of the same element with the same number of protons but differing numbers of neutrons.

Magmatism

Magma: Semi-liquid, hot molten rock found beneath the Earth's surface, within the melted rock and oceanic plate. Temperature ranges from 700°C to 1300°C.
Lava: Magma that reaches the Earth's surface.
Igneous Rocks: Rocks that solidify from magma or lava.
Origin: Magma originates in the lower crust and upper mantle.
Oxygen: Most abundant element found in magma.
Magmatism: The process of magma formation and movement beneath the Earth's crust. Occurs in the asthenosphere (upper mantle below the crust) through convection currents.

Formation of Magma (Partial Melting)

Partial Melting: Different minerals melt at different temperatures and pressures.
Conditions:
- Increase in Temperature:
  - Conduction: Heat transfers from hotter rocks to colder rocks, like at convergent boundaries.
- Decrease in Pressure:
  - Convection: Rocks moving upwards experience a decrease in pressure, triggering melting: known as Decompression Melting, and occurs at Mid-Ocean Ridges.
- Addition of Volatiles:
  - Flux Melting: Water or carbon dioxide are added to hot rocks, lowering the melting point: occurs around subduction zones.

Metamorphism

Metamorphism: A process of changing the form of rocks through heat or pressure without melting the rock.
Metamorphic Rocks: Rocks that have undergone metamorphism.
Changes:
- Mineral composition changes.
- Folding and bending of rocks.
- Recrystallization of minerals.
- Chemical reactions result in new minerals stable at higher pressure and temperature.
Agents and Factors:
- Heat: The most important agent. The geothermal gradient (increase in temperature with depth in Earth's crust) plays a key role.
- Pressure: Increases with depth.
  - Confining/Vertical Stress (Lithostatic): Equal pressure in all directions, causing rocks to become smaller and fractured.
  - Directed/Differential Pressure/Stress: Unequal pressure in all directions affecting crystal shape.
- Protolith: The original, unmetamorphosed rock that the metamorphic rock is derived from.
- Low-grade Metamorphism: Non-foliated rocks with no visible crystal alignments, smooth surfaces, and easily break. Example: Slate
- High-grade Metamorphism: Foliated rocks with visible crystal alignments. Example: Schist, Gneiss
- Time: Metamorphism is a slow process taking tens of millions of years.
- Fluid Phase: Open spaces between mineral grains contain a fluid, mostly water (H2O) containing dissolved ions. Speeds up the process by transporting ions.
  - Metasomatism: Chemical alteration of rocks as a result of fluids.
Types of Metamorphism:
- Regional: Large-scale metamorphism affecting extensive areas of the Earth's crust, producing foliated rocks like Gneiss and Schist. Occurs within the continental crust.