Geo

Age of the Universe: Approximately $13.8\,\text{billion years old}$ .
Origin Theory: The Big Bang Theory.
Age of the Solar System: Approximately $4.6\,\text{billion years old}$ .
Formation Mechanism: Formed from a rotating cloud of gas and dust known as the solar nebula.
Age of Earth: Approximately $4.54\,\text{billion years old}$ .

Crust: Thin, outermost solid layer of Earth.
Mantle: Intermediate layer located between the crust and core; composed mainly of silicate rock rich in iron and magnesium.
Core: Dense central region of Earth; composed primarily of metallic iron ( $\text{Fe}$ ) and nickel ( $\text{Ni}$ ).

Lithosphere: Rigid, brittle outer layer consisting of the crust and uppermost mantle; divided into moving tectonic plates.
Asthenosphere: Weak, ductile/plastic region of the upper mantle beneath the lithosphere that permits tectonic plate movement.
Mesosphere: Stronger, rigid lower mantle located beneath the asthenosphere.
Outer Core: Liquid metallic layer surrounding the inner core.
Inner Core: Solid metallic sphere at Earth's center, maintained in a solid state due to immense pressure despite extreme temperatures.

Mantle Volume: Comprises approximately $82\%$ of Earth's total volume.
Core Volume: Comprises approximately $16\%$ of Earth's total volume.
Percentage Formula:
$\text{Percentage} = \left(\frac{\text{Part}}{\text{Whole}}\right) \times 100$

Moho (Mohorovičić Discontinuity): The boundary separating the crust from the mantle, identified by a sharp increase in seismic wave velocity.
Oceanic Crust vs. Continental Crust:
- Oceanic Crust: Thinner, denser, composed primarily of basalt, and geologically younger.
- Continental Crust: Thicker, less dense, composed primarily of granite, and geologically older.

Active Continental Margin: Coastal margin located adjacent to an active plate boundary; associated with frequent earthquakes, volcanism, and mountain building.
Passive Continental Margin: Coastal margin situated far from active plate boundaries (e.g., the Atlantic Coast of North America).

Plate Tectonics Theory: Unifying framework stating that Earth's rigid lithosphere is broken into plates moving over the asthenosphere.
Continental Drift: Proposed by Alfred Wegener; supported by:
- Jigsaw-like fit of matching continents (e.g., South America and Africa).
- Identical fossil species distributed across widely separated oceans.
- Continuous mountain belts across oceanic gaps.
- Paleoclimatic evidence, such as ancient glacial striations in tropical locations.
Seafloor Spreading: Proposed by Harry Hess; supported by:
- Formation of new oceanic crust at mid-ocean ridges.
- Seafloor age increasing systematically with distance from ridges.
- Symmetrical patterns of magnetic polarity reversals parallel to ridges.
- Sediment thickness increasing farther away from ridge crests.

Movement Rate: Tectonic plates move at average rates of a few centimeters per year ( $\text{cm/yr}$ ).
Kinematic Formulas:
$\text{Distance} = \text{Rate} \times \text{Time}$
$\text{Age} = \frac{\text{Distance}}{\text{Rate}}$
Sample Calculation: Calculate the age of crust located $100\,\text{km}$ from a ridge spreading at $5\,\text{cm/yr}$ :
- Convert distance: $100\,\text{km} = 10,000,000\,\text{cm}$
- Calculate age:
  $\text{Age} = \frac{10,000,000\,\text{cm}}{5\,\text{cm/yr}} = 2,000,000\,\text{years}$

Divergent Boundaries: Plates move apart; new crust is generated.
- Oceanic: Mid-ocean ridges (e.g., Mid-Atlantic Ridge).
- Continental: Rift valleys.
Convergent Boundaries: Plates move toward each other; subduction or collision occurs.
- Oceanic–Continental: Dense oceanic plate subducts beneath continental plate, forming a deep ocean trench and continental volcanic arc (e.g., Andes Mountains).
- Oceanic–Oceanic: Older, denser oceanic plate subducts, forming a deep ocean trench and volcanic island arc (e.g., Aleutian Islands).
- Continental–Continental: Intense collision of buoyant continental crust, producing major mountain ranges without subduction (e.g., Himalayas).
Transform Boundaries: Plates slide past each other horizontally; crust is neither created nor destroyed, generating frequent shallow earthquakes (e.g., San Andreas Fault).
Pangaea: The supercontinent that assembled approximately $250\,\text{million years ago}$ .

Definition of a Mineral: A naturally occurring, inorganic, solid substance with a definite chemical composition and an ordered internal atomic structure.
Diagnostic Physical Properties:
- Color: Visible hue; unreliable due to impurities.
- Luster: Manner in which light reflects from the surface (metallic vs. nonmetallic).
- Streak: Color of the mineral in fine powder form.
- Hardness: Resistance to abrasion or scratching.
- Cleavage: Breakage along smooth, parallel planes of weak atomic bonds.
- Fracture: Irregular breakage pattern (e.g., shell-like conchoidal fracture in quartz).
- Special Properties: Acid reaction ( $\text{HCl}$ reaction with calcite), magnetism (magnetite), taste (halite).

Silicates: Most abundant mineral group in Earth's crust; built from silicon and oxygen.
Silicon-Oxygen Tetrahedron: Basic structural block with formula $\text{SiO}_4^{4-}$ , consisting of $1$ central silicon atom bonded to $4$ surrounding oxygen atoms.
Silicate Structural Configurations:
- Isolated Tetrahedra: Olivine
- Single-Chain: Pyroxene
- Double-Chain: Amphibole
- 2-D Sheet Structure: Mica
- 3-D Framework: Quartz and Feldspar
Non-Silicate Groups:
- Oxides: Oxygen bonded with metallic elements (e.g., Hematite, Magnetite).
- Sulfates: Contain the sulfate complex unit $\text{SO}_4^{2-}$ (e.g., Gypsum).
- Sulfides: Contain sulfur bonded to metals without oxygen $\text{S}^{2-}$ (e.g., Pyrite).
- Halides: Contain halogen ions like chloride or fluoride (e.g., Halite).
- Carbonates: Contain the carbonate complex unit $\text{CO}_3^{2-}$ (e.g., Calcite).
- Native Elements: Composed entirely of a single element (e.g., Gold, Copper, Silver).
Polymorphs: Minerals sharing the same chemical formula but possessing distinct crystalline structures (e.g., Diamond and Graphite, both pure Carbon).