Introduction to Geology

Geology

• Geology encompasses the study of Earth's materials, structure, and active processes.
• This field includes the history of Earth and its inhabited life forms.
• As an umbrella term, geology integrates various sub-disciplines.

Geological Time Scale

• The geological time scale provides a chronological dating system correlating geological strata with time.
• Geologists, paleontologists, and other Earth scientists use this scale to determine the timing and relationships of Earth's historical events.
• The geological time scale is divided into eons, eras, periods, epochs, and ages by duration.
• Eons represent the largest time division, followed by eras, periods, epochs, and ages, in descending order.
• Currently, the Phanerozoic Eon is in effect, beginning approximately 541 million years ago.
• The Phanerozoic Eon includes three eras: the Paleozoic, Mesozoic, and Cenozoic.

Minerals and Crystals

• Minerals are naturally occurring, inorganic solids featuring a definite chemical composition and crystalline structure.
• Minerals serve as the building blocks of rocks.
• Crystals exhibit a solid form with atoms, molecules, or ions arranged in an ordered, repeating pattern across three spatial dimensions.
• Physical properties such as hardness, luster, streak, cleavage, and fracture help identify minerals.
• Hardness indicates a mineral's resistance to scratching and is often measured using the Mohs hardness scale.
• Luster describes how light reflects from a mineral's surface, categorized as metallic, glassy, dull, etc.
• Streak refers to the color of a mineral's powder obtained by rubbing it against a streak plate.
• Cleavage denotes a mineral's tendency to break along specific planes of weakness.
• Fracture describes how a mineral breaks when it does not cleave.

Fossil Records

• Fossils include the preserved remains or traces of ancient organisms.
• Fossils offer key evidence about the history of life on Earth.
• The fossil record constitutes the total collection of discovered fossils.
• Fossil formation occurs through several processes:
  • Permineralization involves minerals precipitating into an organism's empty spaces.
  • Replacement occurs when minerals replace an organism's original material.
  • Compression compacts an organism, leaving a carbonaceous film.
  • Impression forms when an organism decays, leaving an imprint in sediment.
  • Preservation protects an organism in amber, ice, or tar.
• Index fossils are widely distributed, existed for a short time, and are easily recognizable, aiding in correlating rock layers.

Rock Formation

• Rocks include naturally occurring mineral aggregates.
• Igneous, sedimentary, and metamorphic rocks make up the three primary rock types.
• Igneous rocks arise from cooling and solidifying magma or lava.
  • Intrusive igneous rocks cool slowly beneath the Earth's surface, producing large crystals like granite.
  • Extrusive igneous rocks cool quickly on the Earth's surface, creating small crystals or a glassy texture like basalt.
• Sedimentary rocks develop from the accumulation and cementation of sediments.
  • Clastic sedimentary rocks comprise fragments of other rocks, such as sandstone and shale.
  • Chemical sedimentary rocks precipitate from a solution, including limestone and rock salt.
  • Organic sedimentary rocks arise from organic matter accumulation, exemplified by coal.
• Metamorphic rocks form when existing rocks change due to heat, pressure, or chemical reactions.
  • Foliated metamorphic rocks have a layered or banded appearance, like gneiss and schist.
  • Non-foliated metamorphic rocks lack a layered appearance, such as marble and quartzite.
• The rock cycle illustrates how rocks form, break down, and reform.

Plate Tectonics

• Plate tectonics explains that Earth's lithosphere consists of several plates in motion that interact.
• The lithosphere represents Earth's rigid outer layer, including the crust and the uppermost mantle.
• Earth's plates float on the asthenosphere, a semi-molten upper mantle layer.
• Plate boundaries mark the areas where plates interact.
• The main types of plate boundaries consist of:
  • Divergent boundaries: plates move apart, creating mid-ocean ridges.
  • Convergent boundaries: plates collide, resulting in subduction zones and continental collisions.
  • Transform boundaries: plates slide past each other horizontally, such as the San Andreas Fault.
• Plate tectonics triggers geological events, including earthquakes, volcanoes, mountain building, and seafloor spreading.
• Convection currents in Earth's mantle propel plate movement.

Physical Geology/Geomorphology

• Physical geology studies the Earth's materials, structure, and processes.
• Geomorphology focuses on Earth's surface features and the processes that form/modify them.
• Geomorphological processes include:
  • Weathering: breaking down rocks/minerals on Earth's surface.
  • Erosion: removing and transporting weathered materials via wind, water, ice, or gravity.
  • Deposition: eroded materials settling in a new location.
• Landforms, such as mountains, valleys, plains, and coastlines, define Earth's surface features.
• The study of landforms and their formative processes represents a key focus of geomorphology.

Structural Geology

• Structural geology examines rock deformation and resulting structures.
• Structures include folds, faults, and joints.
• Folds are bends in rock layers due to compressional stress.
  • Anticlines are upward-arching folds.
  • Synclines are downward-sagging folds.
• Faults are rock fractures showing evidence of movement.
  • Normal faults feature the hanging wall moving down relative to the footwall, due to tensional stress.
  • Reverse faults show the hanging wall moving up relative to the footwall, due to compressional stress.
  • Strike-slip faults involve rocks moving horizontally past each other, due to shear stress.
• Joints are rock fractures without significant movement.
• Structural geology provides insights into Earth's history and helps locate natural resources like oil, gas, and minerals.

Environmental Geology

• Environmental geology applies geological principles to address environmental problems.
• Environmental geologists study interactions between humans and the geological setting.
• Key study areas include:
  • Natural hazards: earthquakes, volcanoes, landslides, floods, coastal erosion.
  • Water resources: groundwater contamination, water supply issues.
  • Waste disposal: landfill and nuclear waste disposal siting.
  • Mineral resources: mining impacts, resource management practices.
  • Land use planning: geological development constraints, environmental impact mitigation.
• Environmental geology works to lessen human activities' negative environmental impacts and promote sustainable natural resource use.