🌋Physical Geology Unit 1 – Earth's Structure: Intro to Geology

Key Concepts and Terminology

• Geology studies the Earth's structure, composition, processes, and history
• Lithosphere consists of the crust and uppermost mantle, divided into tectonic plates
• Asthenosphere is a partially molten layer beneath the lithosphere that allows for plate movement
• Plate tectonics explains the large-scale motion of Earth's lithosphere
  • Driven by convection currents in the mantle
  • Responsible for the formation of mountains, volcanoes, and earthquakes
• Rock cycle describes the continuous transformation of rocks between igneous, sedimentary, and metamorphic types
• Uniformitarianism states that the same geological processes operating today have operated throughout Earth's history
• Principle of superposition asserts that in a sequence of undisturbed sedimentary rocks, the oldest layers are at the bottom, and the youngest are at the top
• Radiometric dating determines the absolute age of rocks and minerals using the decay of radioactive isotopes (carbon-14, uranium-235)

Earth's Layers and Composition

• Earth is divided into three main layers: crust, mantle, and core
• Crust is the outermost layer, ranging from 5-70 km thick
  • Oceanic crust is thinner (5-10 km) and denser, composed primarily of basalt
  • Continental crust is thicker (30-70 km) and less dense, composed mainly of granite
• Mantle is the layer between the crust and core, approximately 2,900 km thick
  • Upper mantle is solid and rigid, forming the base of the lithosphere
  • Lower mantle is solid but can deform plastically over long time scales
• Core is the innermost layer, divided into the outer and inner core
  • Outer core is liquid, composed primarily of iron and nickel
  • Inner core is solid, composed of iron and nickel, with temperatures reaching 5,400°C
• Lithosphere and asthenosphere are mechanical layers that behave differently in response to stress
• Mohorovičić discontinuity (Moho) is the boundary between the crust and mantle, marked by a sharp increase in seismic wave velocities
• Gutenberg discontinuity is the boundary between the mantle and core, marked by a decrease in seismic wave velocities

Plate Tectonics and Continental Drift

• Plate tectonics theory states that Earth's lithosphere is divided into a series of plates that move relative to one another
• Plates can be oceanic (thin, dense) or continental (thick, less dense)
• Three main types of plate boundaries: divergent, convergent, and transform
  • Divergent boundaries occur where plates move apart, forming new oceanic crust (mid-ocean ridges)
  • Convergent boundaries occur where plates collide, resulting in subduction, mountain building, and volcanism
  • Transform boundaries occur where plates slide past each other, causing earthquakes (San Andreas Fault)
• Seafloor spreading is the process by which new oceanic crust is formed at mid-ocean ridges
• Subduction is the process by which one plate sinks beneath another at convergent boundaries
• Continental drift, proposed by Alfred Wegener, suggests that continents have moved over Earth's surface throughout history
  • Evidence includes matching coastlines (South America and Africa), fossil distributions, and glacial deposits
• Pangaea was a supercontinent that existed about 300 million years ago, before breaking apart into the continents we see today
• Plate motion is driven by convection currents in the mantle, ridge push, and slab pull

Rock Types and Formation Processes

• Three main rock types: igneous, sedimentary, and metamorphic
• Igneous rocks form from the cooling and solidification of magma or lava
  • Intrusive (plutonic) igneous rocks cool slowly beneath Earth's surface, forming large crystals (granite)
  • Extrusive (volcanic) igneous rocks cool rapidly at or near Earth's surface, forming small crystals or glass (basalt, obsidian)
• Sedimentary rocks form from the accumulation and lithification of sediments
  • Clastic sedimentary rocks are composed of rock and mineral fragments (sandstone, conglomerate)
  • Chemical sedimentary rocks form from the precipitation of minerals from solution (limestone, rock salt)
  • Organic sedimentary rocks form from the remains of once-living organisms (coal, chert)
• Metamorphic rocks form from the transformation of pre-existing rocks under high temperature and pressure
  • Foliated metamorphic rocks have a layered or banded appearance due to the alignment of minerals (gneiss, schist)
  • Non-foliated metamorphic rocks do not have a layered appearance (marble, quartzite)
• Rock cycle describes the continuous formation, destruction, and reformation of rocks
  • Weathering and erosion break down rocks into sediments
  • Sediments are transported, deposited, and lithified to form sedimentary rocks
  • Burial, heat, and pressure can transform sedimentary rocks into metamorphic rocks
  • Melting of rocks produces magma, which can cool to form igneous rocks

Geological Time Scale

• Geological time scale is a chronological framework that divides Earth's history into eons, eras, periods, and epochs
• Relative dating determines the order of events without specifying exact ages
  • Principles include superposition, original horizontality, cross-cutting relationships, and inclusions
• Absolute dating determines the age of rocks and minerals using radiometric dating techniques
  • Radioactive isotopes decay at a constant rate, allowing for the calculation of absolute ages
• Precambrian is the longest portion of Earth's history, spanning from the formation of Earth (4.6 billion years ago) to the beginning of the Cambrian Period (541 million years ago)
  • Divided into the Hadean, Archean, and Proterozoic eons
  • Characterized by the formation of Earth's layers, the emergence of life, and the oxygenation of the atmosphere
• Phanerozoic Eon encompasses the last 541 million years of Earth's history
  • Divided into the Paleozoic, Mesozoic, and Cenozoic eras
  • Characterized by the evolution of complex life forms, mass extinctions, and the development of modern ecosystems
• Major events in Earth's history include the formation of the Moon, the Great Oxidation Event, the Cambrian Explosion, the formation and breakup of Pangaea, and the Cretaceous-Paleogene extinction event

Earth's Surface Features and Processes

• Weathering is the breakdown of rocks and minerals at Earth's surface
  • Physical weathering involves the mechanical breakdown of rocks (frost wedging, exfoliation)
  • Chemical weathering involves the chemical alteration of rocks (dissolution, oxidation)
• Erosion is the removal and transportation of weathered material by water, wind, ice, or gravity
  • Fluvial erosion is caused by running water (rivers, streams)
  • Glacial erosion is caused by the movement of glaciers and ice sheets
  • Aeolian erosion is caused by wind
  • Coastal erosion is caused by waves and currents
• Deposition is the settling of transported sediments
  • Deltas form where rivers deposit sediments as they enter a larger body of water
  • Dunes form from the deposition of wind-blown sand
  • Moraines form from the deposition of glacial sediments
• Landforms are natural features on Earth's surface
  • Mountains form through tectonic processes (uplift, folding, faulting) or volcanic activity
  • Plateaus are elevated, flat-topped landforms often formed by uplift and erosion
  • Plains are flat, low-lying areas formed by deposition or erosion
  • Valleys are low areas between mountains or hills, often formed by fluvial erosion
• Karst topography forms from the dissolution of soluble rocks (limestone, dolomite)
  • Features include sinkholes, caves, and underground drainage systems

Tools and Techniques in Geology

• Remote sensing uses satellite imagery and aerial photography to study Earth's surface
  • Landsat and MODIS satellites provide multispectral images for geological mapping and monitoring
  • LiDAR (Light Detection and Ranging) creates high-resolution digital elevation models
• Geophysical methods use physical properties to study Earth's interior
  • Seismic waves (P-waves and S-waves) are used to map Earth's layers and detect earthquakes
  • Gravity anomalies can indicate variations in rock density and help identify subsurface structures
  • Magnetic surveys can detect variations in Earth's magnetic field caused by different rock types
• Geochemical analysis determines the chemical composition of rocks, minerals, and fluids
  • X-ray fluorescence (XRF) and X-ray diffraction (XRD) identify the elemental and mineral composition of samples
  • Stable isotope analysis can provide information about past climates and environments
• Field observations and mapping are essential for understanding local geology
  • Stratigraphic columns depict the vertical sequence of rock units in a given area
  • Geologic maps show the distribution of rock types, structures, and landforms
• Drilling and core sampling provide direct access to subsurface rocks and sediments
  • Boreholes can reach depths of several kilometers
  • Core samples can be analyzed for their physical, chemical, and biological properties

Real-World Applications and Case Studies

• Mineral and energy resource exploration
  • Geologists use various tools and techniques to locate and assess mineral deposits (copper, gold, rare earth elements)
  • Sedimentary basins are explored for oil and gas resources using seismic surveys and well logging
• Natural hazard assessment and mitigation
  • Seismic hazard maps identify areas at risk of earthquakes based on fault locations and historical seismicity
  • Volcanic monitoring systems use seismic, deformation, and gas emission data to forecast eruptions
  • Landslide susceptibility mapping helps identify areas prone to slope failures
• Environmental and engineering geology
  • Geologists assess the suitability of sites for construction projects (dams, tunnels, bridges)
  • Groundwater resources are evaluated and managed using hydrogeological models
  • Contaminated sites are investigated and remediated based on geological and geochemical data
• Paleoclimatology and global change
  • Ice cores, marine sediments, and speleothems provide records of past climate changes
  • Carbon sequestration in geologic formations can help mitigate anthropogenic greenhouse gas emissions
• Planetary geology and astrobiology
  • Comparative planetology uses Earth's geology as a reference for understanding other planetary bodies
  • Mars exploration aims to identify habitable environments and potential signs of past life
  • The study of extremophiles in Earth's harsh environments informs the search for extraterrestrial life