Geology Board Review Practice Flashcards

General Earth Science and Physical Principles

Geology as a formal science involves the study of the Earth, its history, and its physical processes. Scientific investigations in this field rely on the collection of facts through observation and measurement, alongside the development of models and theories. A scientific model is defined as a physical, visual, or mathematical simulation of a scientific idea that has limited evidence and requires further investigation. The Father of Modern Geology is recognized as James Hutton, while George Cuvier was known for advocating Catastrophism. Significant historical milestones include the famous "Earthrise" photograph taken by Apollo 8.

The physical characteristics of the Earth include a total density of $5.51\,g/cc$. The Earth is tilted on its axis by approximately $23.5^{\circ}$, a value also referred to as the Earth's obliquity. The Earth is the densest planet in the solar system, while Saturn is noted as the least dense planet. Our current understanding of the universe's origin is based on the Big Bang Theory, proposed by Georges Lemaitre, while the formation of the Solar System is explained by the Nebular Theory.

Atmospheric and Meteorological Phenomena

The Earth's atmosphere is organized into distinct layers, each with unique thermal and physical properties. The troposphere is the lowest layer where trade winds—easterly surface winds—are found within the tropics (from $0^{\circ}$ to $30^{\circ}$ latitude). The stratosphere contains the ozone layer, which protects the Earth from harmful radiation. The mesosphere is considered the coldest layer of the atmosphere, reaching temperatures of about $-85$ to $-90\,^{\circ}\text{C}$. Maintenance of the atmosphere is attributed to the Outer Core (via the magnetosphere), gravity, and the magnetosphere itself, but not the thermosphere.

Meteorological events like rainbows are produced when light refracts, reflects, and disperses when passing through water droplets. On a larger scale, whirling tropical cyclones in the western Pacific, which can exceed wind speeds of $300\,km/h$, are known as Typhoons. Factors such as the Coriolis effect influence moving masses in a rotating system, creating a force perpendicular to the direction of motion. Global wind patterns are further categorized into cells, with the Polar Cell being the smallest and weakest, and the Hadley Cell characterized by air rising at the equator and sinking at medium latitudes (approx. $30^{\circ}$ N/S).

Hydrology and Glaciology

Hydrology covers the movement and distribution of water across the Earth. Precipitation flowing over the surface is known as runoff. Headwater refers to the source of water for river systems. Rivers transport materials through various loads: the suspended load consists of silt- and clay-sized materials, while the removal of blocks from the channel bed by current is called quarrying. Alluvial channels form in sediments previously deposited in a valley. Characteristic river patterns include dendritic (uniform lithology), trellis (folded terrane), rectangular (fractured/faulted areas), and annular (domes with varying resistance).

Groundwater is stored in the saturated zone (phreatic zone), with the vadose zone being the area between the land surface and the top of the phreatic zone where water is at atmospheric pressure. Capillary fringes are subsurface layers where groundwater seeps up due to tension saturation. Aquifers are permeable strata that transmit water freely, whereas aquicludes/aquitards hinder movement. Geomorphic features in caverns include speleothems: stalactites (ceiling), stalagmites (floor), and columns (joined). Springs occur where the water table intersects the land surface.

Glaciology studies thick ice masses formed over thousands of years. Glacial erosion involves plucking (meltwater freezing in bedrock cracks) and abrasion. Characteristic landforms include fjords (narrow, steep-sided inlets), eskers (winding ridges of stratified sand/gravel), kames, and drumlins. A tarn is a small lake in a cirque, and pater noster lakes are water-filled depressions created by plucking. Ice shelves are large, flat masses of floating ice attached to the coast. Permafrost refers to permanently frozen ground found in tundra climates.

Geomorphology and Surficial Processes

Geomorphology deals with landforms and their development. Key erosional and depositional features include:

• Aeolian Environment: Blowouts (shallow depressions from deflation), Yardargs (sharp irregular ridges of consolidated sediments), and various dunes (Star, Parabolic, Seif/Longitudinal). Barchan dunes are crescent-shaped, while star dunes result from complex wind patterns. A Dreikanter is a ventifact with a pyramidal shape and three wind-abraded facets.
• Desert Landscapes: Inselbergs are isolated residual hills. A bajada is a term for coalescing fans from adjacent canyons. The world's largest non-polar desert is the Sahara in Africa, and the smallest is the Carcross Desert.
• Mass Wasting: Gravity-driven movement of rock and soil. Sliding occurs along a distinct zone of weakness. Rock slides are considered the most catastrophic. Solifluction involves the flow of a saturated surface layer over impermeable ground (common in permafrost). Creep is the slow, gradual downslope movement. Colluvium is the collective term for deposits accumulated at the foot of a slope.
• Coastal Geomorphology: The coast is the boundary between land and sea. Features include spits (ridges of sand projecting into a bay), tombolos (sand ridges connecting islands to mainland), and sea stacks (remnants of sea arches). High-energy waves include swells, which carry energy to distant shores. Tides occur as spring tides (Earth-Moon-Sun aligned) or neap tides.

Mineralogy

Mineralogy focuses on the chemical and physical properties of minerals. A mineral must be a naturally occurring, inorganic solid with a definite chemical structure (e.g., malachite). Earth's most abundant mineral is bridgmanite. Basic crystal systems include Isometric, Tetragonal, Hexagonal, Orthorhombic, Monoclinic, and Triclinic. Physical properties include:

• Hardness: Measured by the Mohs Scale. Minerals include Talc ($1$), Gypsum ($2$), Calcite ($3$), Fluorite ($4$), Apatite ($5$), Orthoclase ($6$), Quartz ($7$), Topaz ($8$), Corundum ($9$), and Diamond ($10$).
• Optical Properties: Pleochroism (color change with orientation), Iridescence (reflective interference), and Tenebrescence (color change upon exposure to UV light).
• Luminescence: Fluorescence (immediate), Phosphorescence (delayed), and Triboluminescence (visible light when struck/rubbed).
• Electrical Properties: Piezoelectricity (charge from pressure) and Pyroelectricity (charge from heat).

Chemical bonding types include Ionic, Covalent (hard, high melting point), and Metallic. Goldschmidt's rules explain isomorphous substitution based on atomic charge and radius. Polymorphism describes minerals with the same composition but different structures (e.g., Diamond/Graphite, or the high-pressure SiO2 polymorph Stishovite). Metamict minerals have had their internal structure disrupted by radiation while maintaining external form.

Petrology: Igneous, Sedimentary, and Metamorphic

Petrology is the study of rock origin (petrogenesis) and description (petrography).

Igneous Petrology:

• Magma Components: Melt (liquid), Volatiles (gas), and Crystals.
• Textures: Ophitic (random plagioclase laths in pyroxene), Sieve (mixing process indication), and Glomeroporphyritic (clusters of phenocrysts).
• Classification: Based on silica content: Ultramafic ($< 45\%\,SiO_2$), Basic ($45\text{--}52\%\,SiO_2$), Intermediate ($52\text{--}66\%\,SiO_2$), and Acidic ($> 66\%\,SiO_2$).
• Plutons: Batholiths ($> 100\,km^2$), Lopoliths (saucer-shaped), and Phacoliths (lens-shaped in fold crests).

Sedimentary Petrology:

• Clastic Rocks: Conglomerate ($> 2\,mm$ clasts, matrix limit $70\%$), Shale (mostly silt/clay).
• Non-Clastic: Limestone (carbonate), Chert (siliceous).
• Classification: Rudite ($> 2\,mm$), Arenite ($0.0625\text{--}2\,mm$), and Lutite ($< 0.0625\,mm$).
• Carbonates: Dunhan classification includes Mudstone, Wackestone, Packstone, and Grainstone. Ooids are spherical bodies $< 2\,mm$, while pisoids are $> 2\,mm$.

Metamorphic Petrology:

• Factors: Heat (most important), Pressure, and Chemically active fluids.
• Facies: Defined by P-T conditions. High P, Low T (Blueschist); High P, High T (Eclogite); Moderate P-T (Amphibolite).
• Index Minerals: Isograds are lines on a map marking the first appearance of an index mineral (e.g., Garnet, Staurolite).

Structural Geology and Tectonics

Deformation involves changes in rock shape/size due to stress (Force/Area). Stress types include Compression, Tension, and Shear.

• Faults: Based on Anderson’s classification. Normal fault (hanging wall moves down, tensional), Reverse fault (hanging wall moves up, compressional), and Strike-slip (horizontal movement). The Philippine Fault Zone is a left-lateral strike-slip fault.
• Folds: Anticlines (beds dip away from center), Synclines (beds dip toward center), and Domes/Basins. Isoclinal folds have parallel limbs.
• Plate Tectonics: Divergent (constructive), Convergent (destructive), and Transform boundaries. Subduction involves lithosphere sinking into the mantle. Isostasy is the concept of the crust floating in gravitational balance.
• Earthquakes: Measured by Magnitude (energy) and Intensity (damage). The underground focus is the hypocenter; the surface point is the epicenter. Waves include P-waves (compressional, fastest), S-waves (shear), Love waves (horizontal surface), and Rayleigh waves (elliptical surface).

Historical Geology and Paleontology

Historical geology sequences events using relative dating (laws of Superposition, Inclusion, and Cross-cutting Relationships) and absolute dating (radioactive isotopes).

• Geologic Time: Eons (Phanerozoic), Eras (Paleozoic, Mesozoic, Cenozoic), Periods, and Epochs.
• Eras: Paleozoic (Age of Invertebrates/Fishes), Mesozoic (Age of Reptiles), Cenozoic (Age of Mammals).
• Key Events: Cambrian (Great Dying of Trilobites), Devonian (Age of Fishes), Permian (Great Dying mass extinction), and Cretaceous (extinction of dinosaurs due to meteor impact).
• Paleontology: Taphonomy is the study of fossilization processes. Trace fossils (ichnofossils) include Cubichnia (resting), Repichnia (crawling), and Domichnia (dwelling).

Applied and Economic Geology

Applied geology integrates geological knowledge for resource extraction and engineering.

• Mining: Ore is a profitable mineral concentration; protore is sub-economic. Key terms include Cut-off grade and Gangue. Mining methods include Block Caving, Longwall, and Room and Pillar. Legislation in the Philippines includes RA 7942 (Mining Act) and RA 10166 (Geology Profession Act).
• Petroleum: Requires a source rock (organic-rich shale), reservoir rock (porous sandstone/limestone), and a seal/trap. Kerogen maturation stages are Diagenesis, Catagenesis (oil window), and Metagenesis (gas window).
• Geophysics:
  • Gravity: Detects density variations using Gravimeters.
  • Magnetic: Detects magnetic susceptibility.
  • Resistivity: Measures ability of ground to conduct electricity (water/metals decrease resistance).
  • Seismic: Reflection and Refraction used for subsurface mapping.
• Geochemistry: Uses X-ray Fluorescence (XRF) for whole-rock chemistry and X-ray Diffraction (XRD) for mineral identification.

Geologic Equation and Formula Reference

Mathematical applications in geology include:

• Seismic Velocity:$V_p = \sqrt{\frac{k + \frac{4}{3}\mu}{\rho}}$ Where $V_p$ is Primary Velocity, $k$ is bulk modulus, $\mu$ is shear modulus, and $\rho$ is density.

• Radioactive Decay:$N = N_0 \times \left(\frac{1}{2}\right)^{\frac{t}{h}}$ Where $N$ is final amount, $N_0$ is initial amount, $t$ is time elapsed, and $h$ is half-life.

• Strike and Dip Calculation (Apparent to True):$\tan(\delta) = \frac{\tan(\alpha)}{\sin(\beta)}$ Where $\delta$ is true dip angle, $\alpha$ is apparent dip angle, and $\beta$ is the angle between strike and apparent dip trend.

Questions & Discussion

Q: What is the coldest layer of the atmosphere? A: The Mesosphere, with temperatures around $-85$ to $-90\,^{\circ}\text{C}$.

Q: Who is the father of modern Geology? A: James Hutton.

Q: What is the thickness measurement for a sedimentary bed? A: A bed is the smallest formal lithostratigraphic unit; thickness can vary but typically greater than $1\,cm$ (lamination is $< 1\,cm$).

Q: What is the gravitational pull on the moon? A: $1.62\,m/s^2$.

Q: What was the magnitude of the Bohol October 2013 earthquake? A: $M_s\,7.2$.

Q: What is the deepest drillhole in human history? A: The Kola Superdeep Borehole.