GEOLOGY LESSON 1 AND 2

• Geology is the scientific study of Earth's structure, composition, and the processes shaping its surface.
• Geologists study rocks, minerals, and Earth's interior, reconstruct Earth's history, assess natural hazards, and provide insights for resource exploration and environmental management.

Branches of Geology

• Physical Geology focuses on Earth's structure, composition, physical properties, rocks, minerals, and surface features.
• Crystallography studies the arrangement and bonding of atoms in crystalline solids and the geometric structure of crystal lattices.
• Mineralogy examines all aspects of minerals, including physical properties, chemical composition, internal crystal structure, occurrence, distribution, and formation conditions.
• Petrology is the study of rocks (igneous, metamorphic, and sedimentary) and the processes that form and transform them.
• Structural Geology studies the form, arrangement, and internal structure of rocks, especially on a moderate to small scale.
• Stratigraphy describes rock successions and their interpretation in terms of a general time scale.
• Paleontology studies the life of the geologic past through the analysis of plant and animal fossils, including microscopic ones.
• Historical Geology reconstructs the geological history of Earth.
• Economic Geology studies the distribution of mineral deposits, economic factors in their recovery, and assessment of reserves.
• Hydrogeology studies the occurrence, distribution, and movement of water beneath Earth's surface.
• Engineering Geology applies geologic information to construction sites for foundation design and support.

Crystals vs Minerals

• 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, forming from minerals or other substances like organic or synthetic materials.

Rocks vs Soils

• Rocks are aggregates of minerals found in the Earth's crust, consisting of one or more minerals.
• Soils are unconsolidated materials from the disintegration of different rock types, composed of a mixture of minerals, organic matter, gases, liquids, and organisms.

Geotechnical Engineering

• Geotechnical engineering studies the engineering behavior of earth materials, using principles of soil and rock mechanics, geology, geophysics, and hydrology.
• Foundation engineering applies geology, soil mechanics, rock mechanics, and structural engineering to design and construct foundations for civil engineering structures.
• Rock mechanics studies the fundamental principles governing the behavior of all rock and rock masses.
• Soil mechanics studies the fundamental principles governing the behavior of all soil and soil masses.

Historical Geology

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

Types of Ages

• Relative time (relative age) measures time using comparison methods.
• Absolute time (absolute age) measures time using actual numbers.

Measuring Earth's Age

• Earth's relative age is measured using rock layers and faults.
• Earth's absolute age is measured using radioactive dating.

Radioactive Dating

• Radioactive dating involves the breakdown of atoms to form different isotopes.
• Carbon-14 decays to Carbon-12.
• Energy is given off in the form of gamma rays, alpha particles, and beta particles.

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

• 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.

Fundamental Theories of Historical Geology

• Two theories are Uniformitarianism and Catastrophism.

Theory of Uniformitarianism

• Uniformitarianism suggests that the landscape developed over long periods through slow geologic processes, proposed by James Hutton in 1785 and expanded by Charles Lyell in the 1830s.
• "The present is the key to the past."

Lyell's Uniformitarianism Propositions

• Uniformity of law: natural laws are constant across time and space.
• Uniformity of methodology: use present-day analogies to explain the geological past.
• Uniformity of kind: past and present causes are the same and produce the same effects.
• Uniformity of degree: geological circumstances have remained the same over time.

Theory of Catastrophism

• Catastrophism is the idea that the earth has been affected by sudden, short-lived, violent events.
• First popularized by Georges Cuvier in the 19th century.

Impact Hypothesis

• Giant impact hypothesis: A large planetesimal impacted the early earth, blowing out rocky debris, which remelted and formed the moon.

Fundamental Principles of Historical Geology

• Contact: distinct surface between two unlike bodies of rocks
• Stratum: single layer/bed of rock
• Strata: multiple layers/beds of rocks
• Stratigraphy: study of strata
• Formation: a body of rock with distinctive structure that is bounded by contacts
• Outcrop/Exposure: locations where rocks are exposed at the earth's surface

Steno's Laws of Historical Geology

• Nicolaus Steno formulated these in 1669.

Steno's Law of Superposition

• In an undeformed sequence of sedimentary rocks, each bed is younger than the one below it and older than the one above it.

Steno's Law of Original Horizontality

• Sedimentary rocks are horizontal because original sediments were horizontal.
• Steeply inclined strata have been moved from their original position.
• Strata that are either perpendicular to the horizon or inclined to it, were at one time parallel to the horizon.

Steno's Law of Lateral Continuity

• Strata originally extended in all directions until they thinned to zero at their edges of deposition.

Unconformity Definition

• Unconformities are gaps in the geologic record, indicating episodes of crustal deformation, erosion, and sea-level variations.
• Unconformities represent times when deposition stopped, erosion occurred, and deposition resumed.

Types of Unconformities

• Angular Unconformities: older sediments are tilted, truncated by erosion, and then a younger package of sediments are deposited on this erosion surface.
• Disconformities: erosion surface between two packages of sediment, but the lower package of sediments was not tilted prior to deposition.
• Nonconformities: unconformities that separate igneous or metamorphic rocks from overlying sedimentary rocks, indicating a long period of erosion.

Summarized Geologic Time Scale

• Paleozoic Era: Age of invertebrates
  • Cambrian Period
  • Ordovician Period
  • Silurian Period
  • Devonian Period
  • Carboniferous Period
  • Permian Period
• Mesozoic Era: Age of dinosaurs and reptiles
  • Triassic Period
  • Jurassic Period
  • Cretaceous Period
• Cenozoic Era: Age of mammals
  • Tertiary Period
  • Quaternary Period