Introduction to Geology

• Geology is the scientific study of Earth's structure, composition, and surface processes
• Geologists study rocks, minerals, and Earth's interior using fieldwork, analysis, and technology
• Geology helps understand Earth's history, natural hazards, resource exploration, and environmental management

Branches of Geology

• Physical Geology studies Earth's structure, composition, physical properties, rocks, minerals, and surface features
• Crystallography studies the arrangement and bonding of atoms in crystalline solids and crystal lattices' geometric structure
• Mineralogy studies all aspects of minerals, including their physical properties, chemical structure, occurrence, distribution, and origins
• Paleontology studies past life by analyzing plant and animal fossils preserved in rocks, including microscopic ones
• Historical Geology uses geology principles to reconstruct Earth's geological history
• Economic Geology studies the distribution of mineral deposits and the economic considerations of their recovery and reserve assessment
• Hydrogeology studies the occurrence, distribution, and movement of water beneath Earth's surface
• Geotechnical Engineering, a Civil Engineering area, studies earth material behavior using soil and rock mechanics, geology, geophysics, and hydrology

Minerals vs. Crystals

• Minerals are naturally occurring, inorganic substances with a definite chemical composition and crystalline structure
• Crystals are solids with a regular, repeating arrangement of atoms, molecules, or ions
• Crystals can form from minerals, organic materials (e.g., sugar crystals), or synthetic materials (e.g., silicon crystals)
• Petrology studies igneous, sedimentary, and metamorphic rocks, as well as the processes that form and transform them

Rocks vs. Soil

• Rocks are aggregations of minerals found in Earth's crust
• Soil is unconsolidated material from the disintegration of different rock types
• Rocks consist of one or more minerals
• Soil consist of minerals, organic matter, gases, liquids, and organisms
• Igneous, sedimentary, and metamorphic are different types of rocks
• Coarse-grained (gravel, sand), fine-grained (silt, clay), and highly organic (peat) are different types of soil
• Structural Geology studies the form, arrangement, and internal structure of rocks
• Stratigraphy describes rock successions and their interpretation in terms of a general time scale, used in petroleum geology and archaeology

Historical Geology

• Historical Geology studies changes to Earth and life in time and space

Types of Ages

• Relative time (relative age) involves comparing different entities
• Absolute time (absolute age) generates a hard number for the age of an entity

Measuring Earth's Relative Age

• Relative age can be acquired from the use of rock layers including faults

Measuring Earth's Absolute Age

• Radioactive dating is a measure of measuring absolute age, where isotope decay is the key component

Radioactive Dating

• Radioactive dating uses the breakdown of atoms to form different isotopes of the same or new elements

Common radioactive dating techniques

• Uranium-lead dating (U-235 to Pb-207)
• Samarium-neodymium dating (Sm-147 to Nd-143)
• Potassium-argon dating (K-40 to Ar-40)
• Rubidium-strontium dating (Rb-87 to Sr-87)
• Uranium-thorium dating (U-234 to Th-230)
• Radioactive carbon dating (C-14 proportions)
• Half-life is the time it takes for half of the original atoms to decay
• Uranium-238 has a half-life of 4.5 billion years
• Carbon-14 has a half-life of 5,700 years
• Oxygen has a half life of 19 seconds
• In a substance with a half life indicated, half of the original substance will be gone

Fundamental Theories of Historical Geology

• Catastrophism and Uniformitarianism are two fundamental theories

Theory of Uniformitarianism

• Uniformitarianism (gradualism) says landscapes develop over long periods through slow geologic and geomorphic processes
• James Hutton proposed it in 1785 based on natural history, and Charles Lyell expanded it in the 1830s
• "The present is the key to the past"
• Hutton says rock breaks down into smaller particles carried downstream, deposited, and forming new sediment layers
• He predicted these deposits would form new rock over time
• Hutton thought new rock would be raised to create new landforms, restarting the cycle

Lyell's Uniformitarianism Propositions

• Laws of nature are constant across time and space
• Analogies from today are appropriate to explain geological past using hypotheses
• Past and present causes are the same in kind, producing the same effects
• Geological circumstances have remained consistent over time

Theory of Catastrophism

• Catastrophism proposes that sudden, short-lived, violent events have shaped Earth
• Georges Cuvier popularized it in the 19th century, suggesting new life forms migrated after local floods
• Geological epochs ended with catastrophes like great floods, mountain formation, or asteroid impacts

Giant Impact Hypothesis

• A large planetesimal impacted early Earth ~4.5 billion years ago, ejecting rocky debris that remelted and formed the Moon

Principles of Historical Geology Terminology

• Contact: A distinct surface between two unlike rock masses
• Stratum: A single layer/bed of rock
• Strata: Multiple layers/beds of rock
• Stratigraphy: The study of strata
• Formation: A rock mass with a distinct structure bounded by a contact
• Outcrop/Exposure: Locations where rocks are exposed

Nicolaus Steno's Formulations

• Nicolaus Steno, a Danish physician, created formulations in 1669 to understand Tuscany, Italy rocks and objects
• Steno's Law of Superposition: In an undisturbed sequence, each sedimentary rock bed is younger than the one beneath and older than the one above
• Steno's Law of Original Horizontality: Sedimentary rocks are originally horizontal and tilted due to being moved from their original position
• Steno's Law of Lateral Continuity: Strata extend in all directions until they taper to zero, so matching strata on opposite valley sides are correlated
• Steno's Law of Intrusive Relationships: A body or discontinuity that cuts across a stratum formed after that stratum
• Steno's Law of Cross-Cutting Relationships: Invading igneous rock is younger than the intruded rock

Unconformity

• Unconformities represent gaps in the geologic record indicating crustal deformation, erosion, and sea level changes
• They signify times of stopped deposition, erosion, and resumed deposition

Types of Unconformities

• Angular unconformities involve tilted, eroded older sediments overlain by younger sediments
• Disconformities are erosion surfaces between sediment packages where the lower package was not tilted
• Nonconformities separate igneous or metamorphic rocks from overlying sedimentary rocks, indicating a long period of erosion

Minerals and Elements

• Minerals are naturally occurring, solid earth materials formed by geologic processes
• Matter is composed of atoms, the smallest part of a chemical element
• Isotopes are atoms of the same element with different numbers of neutrons
• Radioisotopes are unstable isotopes that undergo nuclear decay

Minerals and Compounds

• Formally defined as a naturally formed element or chemical compound. This chemical compound must be
  • Formed naturally (e.g., excludes human diamonds),
  • Normally exist as a solid (e.g., excludes fluids),
  • Possess a specific chemical formula
  • Have a characteristic crystalline structure.
• Compounds are substances composed of two or more elements with a chemical formula
• Minerals are either elements or compounds

Identifying Minerals

• Identifying minerals involves chemical composition, and physical characteristics

Minerals and Chemical Bonding

• Chemical bonding occurs via attraction of atoms, electron sharing
  • Covalent bonds are the sharing of electrons (e.g., diamond)
  • Ionic bonds are the attraction of negatively and positively charged ions, usually dissolving in water (e.g., halite)
  • Van der Waals bonds are weak attractions between ion chains bonded by stronger covalent/ionic bonds (e.g., graphite)

Properties

• Metallic bonds are the attraction between metal atoms (e.g., gold)
• Some minerals share chemical formulas but differ in physical characteristics

Rock-Forming Minerals

• Silicates include silicon (Si) and oxygen (O), the most common rock-forming minerals
• Carbonates contain the carbonate ion (CO3^2-), and are major components of limestone and marble
• Oxides contain the oxide anion (O2-) bonded to metal ions
• Halides are minerals with a dominant halide (halogen, Group 17) anions (F, Cl, Br, I-)
• Sulfides contain sulfur anions (S^2-) or disulfide anions (S2^2-)

Silicates

• Silicates are pyramidal-shaped tetrahedrons with large oxygen ions at the corners and small silicon ion in the center, being colorless or clear and fracturing similar to glass

Silicate: Quartz

• SiO2 exhibits fractures conchoidally like shells

Silicates: Feldspars

• Feldspars are aluminosilicates plus Si, O, and Al, plus K, Na, Li, or Ca in a Si-O tetrahedron network
  • Feldspars make up 60 percent of what is in the crust
  • Feldspars are commercially important in the ceramics and glass industries
  • Alkali feldspar contains K, Na, Al, such as pink granite (Sanidine, Orthoclase)
  • Plagioclase feldspar contains Na and Ca (Oligoclase, Albite)
• Carbonates contain the carbonate ion CO3^2- and form limestone and marble
• Oxides are minerals containing the oxide anion 02 bonded to one or more metal ions
• Halides are minerals with a dominant halide F, Cl, Br, I-
• Sulfides are a type of minerals that tend to degrade the environment when oxidized

Streak

• Streak is the color of a mineral substance when it has been ground to a fine powder
• Mineral Identification can be assisted from the chemical composition

Luster

• Luster refers to whether the mineral is opaque or transparent
• Metallic and Nonmetallic are the two categories of luster
• Some forms of luster include:
  • Dull: Having the look of earth or clay
  • Resinous: Possessing a sheen resembling a smooth-surfaced plastic
  • Pearly: Light reflecting from mineral layers give it a luster reminiscent of pearls
  • Greasy: Gives off the look of being covered in a layer of oil
  • Silky: The luster reminiscent of silk
  • Vitreous: Reflective quality of a broken glass
  • Adamantine; Sparkling reflection

Hardness

• Hardness is how hard it is for a mineral surface to be scratched
• In terms of the MOHS Scale of Hardess, if a score is high, the level of difficulty is increased

Cleavage

• Cleavage is the tendency of a mineral to split with different levels of effectiveness. They include eminent, perfect, distinct, difficult, imperfect and indistinct

Fracture

• Fracture occurs when a mineral splits in a direction which does not serve as a plane of perfect or distinct cleavage, instead breaking off at a difficult plane

Geology Timeline

• Gems are silicates that form according to a geological timeline in different periods
• Gems like garnets (January), amethysts (February), aquamarine (March), diamonds (April), emeralds (May), rubys (July), sapphires (September), topaz (November), and blue zircon (December) are good examples of silicates in action

Petroclogy

• Topic four is about petrology

Igneous Rocks

• Igneous Rocks derive from inside of the Earth

• Igneous Rocks derive either from magma or lava. Magma is on the inside (earth surface) and lava on the outside (atmosphere)

  • Felsic magmas are highly viscous
  • Mafic magmas: has a lower viscosity
  • Ultramafic magma; has a very low viscosity and high eruption temperatures

Types of Igneous Rocks

• There are types of extrusive and intrusive igneous rocks
  • The inside rocks cool down slowly but outside rocks col down quickly

Forms of Lava

• Volcanoes are landforms made and built by repeated eruptions of lava and ash over time

Igneous Intrusions

• Forms like fissures, volcanic cones, magma chambers, dykes, and fresh lava flows

Igneous Textures

• Igneous textures can be Aphanitic, Porphorytic, Glassy, and Vesicular

Sedimentary Rocks

• Sedimentary rocks can be deposited into the sea, in stratified layers

Sediments

• Soil material subsequently transported away from its source, mostly by water sediments

Sedimentary Materials

• Sandstone includes quartz crystals
• Water transport allows for sediment sorting
• The processes of lithification, cementation, and crystallization transform the materials

Sedimentary Structures

• Stenos law of original horizontality: layers of sediment are originally deposited horizontally under the action of gravity, but can be changed due to disturbances
• Types of sedimentary structures include stratification/bedding, cross-bedding, graded bedding, ripple marks, mud cracks, and fossils

Sedimentary Environments

• These include depositional environments categorized into continential, tranistional, marine, evaporator, glacial, an dvolcanic environments, which can have subcategories