Geologic Time Scale PDF

Definition of Geologic Time Scale (GTS) Divides Earth's history based on life forms and events. Composed of eons, eras, periods, epochs, and ages (in descending order of duration). Based on stratigraphy and fossil records; fossils mark beginnings/ends of intervals. Stan...

Definition of Geologic Time Scale (GTS) Divides Earth's history based on life forms and events. Composed of eons, eras, periods, epochs, and ages (in descending order of duration). Based on stratigraphy and fossil records; fossils mark beginnings/ends of intervals. Standardized in the International Chronostratigraphic Chart by ICS. geochronologic units - the continuous time interval between the deposition of the lowest and highest strata within the unit.. International Chronostratigraphic Chart, which is maintained by the International Commission on Stratigraphy (ICS). Geologic Time Divisions Eons: Longest division; spans billions of years (e.g., Hadean, Archean). Eras: Hundreds of millions of years, grouped within eons (e.g., Paleozoic). Periods: Tens to hundreds of millions of years; divisions within eras. Epochs: Shorter than periods; last tens of millions of years. Ages: Shortest division, with some units even smaller, like chrons. Principles Behind GTS 1. Nicholas Steno’s Principles: Danish Physician o Superposition: Bottom layer is oldest. o Horizontality: Layers were originally horizontal. o Original Lateral Continuity: Layers extend until interrupted by other rock layers. 2. Historical Contributions: o Abraham Gottlob Werner: Proposed all rocks originated in oceans (Neptunism). o James Hutton: Scottish physician and geologist "Uniformitarianism" (present processes explain the past). o William Smith: The principle of Biologic succession; unique fossils identify specific time periods. o Charles Lyell: The principle of cross-cutting relationships and Inclusion principle o Charles Darwin: Theory of natural selection as a mechanism of evolution. The theory of natural selection was credited to Darwin (along with Alfred Russel Wallace), and he went on to write the famous "Origin of Species." Methods of Determining Fossil Age 1. Relative Age Dating: Uses layer positions for sequence dating. 2. Relative Dating with Index Fossils: Widespread, short-lived fossils help correlate layers. 3. Absolute Age Dating: Uses isotopic decay rates to assign specific ages. 4. Radiocarbon Dating: Carbon-14 decay for organic materials up to ~70,000 years old. 5. Uranium-Lead Dating: Uranium isotopes Effective for igneous rocks, millions to billions of years old. Key Time Abbreviations Ga (Gya): Billion years ago. Ma (Mya): Million years ago. Ka (Kya): Thousand years ago Precambrian Eon Hadean Eon (4.6 - 4.0 billion years ago) Archean Eon (4.0 - 2.5 billion years ago) Proterozoic Eon (2.5 billion - 541 million years ago) Phanerozoic Eon Paleozoic Era Cambrian Period (541–485 million years ago) Ordovician Period (485–443 million years ago) SILURIAN PERIOD (443 - 419 million years ago) DEVONIAN PERIOD (419 - 359 million years ago) CARBONIFEROUS PERIOD (359 - 299 million years ago) PERMIAN PERIOD (299 - 252 million years ago) MESOZOIC ERA - Transition from Paleozoic to Mesozoic fauna; rise and fall of dinosaurs. TRIASSIC PERIOD (251 - 199.6 million years ago) JURASSIC PERIOD (199.6 to 145 million years ago) CRETACEOUS PERIOD (145 to 65 million years ago) CENOZOIC ERA (66 million years ago to present) Etymology: "Cenozoic" derives from Greek, meaning “recent life.”  PALEOGENE PERIOD (66 to 23 million years ago) o Paleocene (66 to 56 million years ago) o Eocene (56 to 34 million years ago) o Oligocene (34 to 23 million years ago) NEOGENE PERIOD (23 to 2.6 million years ago) o Miocene (23 to 5 million years ago) o Pliocene (5 million years ago to 2.6 million years ago) QUATERNARY PERIOD (2.6 million years ago to present) o Pleistocene Epoch (2.6 MYA to 10,000 years ago) o Holocene Epoch (10,000 years ago to present) Earth’s Timeline and Geological Events 1. 4.6 Billion Years Ago: Formation of Earth; initial molten state; moon formation stabilized tilt. 2. 4.0 – 2.5 Billion Years Ago: Cooling, oceans formed; emergence of early life (cyanobacteria), triggering the Great Oxygenation Event. 3. 541 – 245 Million Years Ago: Cambrian Explosion; diversification of life and hard- shelled invertebrates. 4. 245 – 66 Million Years Ago: Age of Reptiles and Dinosaurs; dominance of dinosaurs and existence of Pangea. 5. 66 Million Years Ago – Present: Age of Mammals; extinction of dinosaurs leads to mammal evolution and emergence of Homo sapiens. Applications of the Geological Time Scale 1. Age Dating: Determines ages of rocks, fossils, and geological formations. 2. Correlation of Rock Strata: Reconstructs Earth’s history and geological relationships. 3. Resource Exploration: Guides exploration in petroleum, mineral, and mining industries. 4. Climate Change Studies: Analyzes past climate conditions and mechanisms. 5. Evolutionary Biology: Understands development of life and interspecies connections. 6. Archaeology: Ages archaeological sites and artifacts for cultural evolution studies. Limitations and Criticisms of the Geological Time Scale 1. Incomplete Fossil Record: Gaps in fossils make precise dating difficult. 2. Assumptions About Rates of Change: Based on assumptions that can be challenged and revised. 3. Dating Techniques: Absolute dating methods have limitations and sources of error. 4. Conflicting Interpretations: Different scientific interpretations can lead to disagreements about timing and relationships. 5. Controversies: Disagreements exist regarding mass extinctions and origins of species. 1. Earth Structure Layers: Earth is divided into the crust, mantle, outer core, and inner core, each with unique compositions and characteristics. o Crust: Outer shell, composed mostly of solid basalt and granite. ▪ Continental Crust: Thicker, under continents. ▪ Oceanic Crust: Thinner, under ocean basins. ▪ Mohorovicic Discontinuity (Moho): Boundary between the crust and mantle. o Mantle: Largest layer (84% of Earth’s volume), mostly solid, with a partially molten upper layer. ▪ Upper Mantle: Includes the lithosphere (solid) and asthenosphere (semi- fluid). ▪ The lithosphere is the solid, outer part of Earth. ▪ The asthenosphere is the denser, weaker layer beneath the lithospheric mantle ▪ Lower Mantle: Solid, contributes to heat transfer within Earth. o Outer Core: Liquid layer made of iron and nickel; generates Earth’s magnetic field. o Inner Core: Solid, high-pressure iron and nickel core at Earth’s center. 2. Plate Tectonics and Movement Plate Tectonics Theory: Earth’s lithosphere is broken into large plates that move due to interactions with the semi-molten asthenosphere.  o Plate Movements: Plates move at rates of 5-10 cm/year, causing earthquakes, volcanic activity, mountain formation, and ocean basin changes. Supercontinents: Pannotia: Hypothetical supercontinent (~633-573 mya). Gondwana: Included South America, Africa, India, Australia, and Antarctica (550-150 mya). Pangea: Most recent supercontinent, covering 1/3 of Earth’s surface (336-175 mya). Plate Movement Types: Convergent Boundaries: Plates push together, forming mountains. Divergent Boundaries: Plates pull apart, forming new ocean basins. Alfred Wegener: The Origin of Continents and Oceans Proposed Continental Drift (1912), noting similar fossils and rock formations on separate continents. Mechanisms Driving Plate Movement: Mantle Convection: Heat transfer from core to lithosphere. Ridge Push: Plates slide down the raised asthenosphere near mid-ocean ridges. Slab Pull: Cold, dense plates sink into the mantle. Slab Suction: Pulls down plates in subduction zones, increasing movement. 3. Plate Boundaries A plate boundary is a zone where there's a notable change in the velocity of one lithospheric plate relative to the adjacent plate. Types of Plate Boundaries Convergent Boundary Divergent Boundary Transform Boundary Divergent Boundary Characteristics: Plates move away from each other, creating new crust as magma rises and solidifies. Formation: Continuous reshaping and formation of Earth’s crust. Philippine Examples: o Philippine Rise (Mindoro and Palawan regions): Oceanic crust created as tectonic plates pull apart. o Sulu Sea: Shows rifting between the Philippine Sea Plate and surrounding plates. Convergent Boundary Characteristics: Plates collide, resulting in mountain formation, volcanic activity, and earthquakes. Philippine Example: o Manila Trench: Philippine Sea Plate subducts beneath the Eurasian Plate, causing volcanic arcs and seismic activity (e.g., Bataan Peninsula, Zambales Mountain Range). Types of Convergent Boundaries: Continental-Continental: Collision leads to mountain ranges (e.g., Himalayas). Oceanic-Oceanic: Creates deep-sea trenches and volcanic island arcs (e.g., Mariana Trench). Oceanic-Continental: Denser oceanic plate subducts, forming trenches and volcanic arcs (e.g., Andes Mountains). Transform Boundary Characteristics: Plates slide horizontally past each other, redistributing stress. Philippine Example: o Philippine Fault: Major fault system with significant seismic activity where the Philippine Sea Plate slides past the Eurasian Plate. 4. Plate Tectonics and Volcanoes Plate Boundaries: o Convergent Boundaries: Create volcanic arcs. o Divergent Boundaries: Allow magma to rise, creating new crust. o Transform Boundaries: Don’t typically create volcanoes but affect nearby volcanic activity. Magma Production: Movement in subduction zones produces magma that can erupt as volcanoes. Hotspots: Magma rises through mantle areas not at plate boundaries, forming volcanic islands (e.g., Hawaii). 5. Earthquakes and Plate Tectonics Earthquakes are closely linked to tectonic plate movement, mainly occurring at plate boundaries. Distribution: Concentrated around plate boundaries, especially in the Pacific Ring of Fire.  Mechanism: o Tectonic plates meet and get “stuck,” building stress. o When stress exceeds strength, plates slip, releasing energy as seismic waves. Fault Types: o Reverse Fault: Compression at convergent boundaries (e.g., 2008 Sichuan earthquake). o Normal Fault: Extension at divergent boundaries (e.g., 2011 Virginia earthquake). o Strike-Slip Fault: Horizontal sliding at transform boundaries (e.g., 1990 Luzon Earthquake). Impact: Earthquakes can shake, crack, and displace the ground, affecting infrastructure and safety. A. Definition of Faults 1. Earth's Crust Composition: o Made of tectonic plates (7 major: African, Antarctic, Eurasian, Indo-Australian, North American, Pacific, South American). o Plates move due to convection currents in the mantle. 2. Plate Boundaries: o The meeting point of two tectonic plates where faults form. o Faults accommodate plate movement and can cause earthquakes. 3. Definition of Fault: o A crack or fracture in the Earth's crust where rocks have moved or been offset. o Ranges from microscopic cracks to large fault systems. 4. Components of Fault: o Hanging Wall: The block above the fault plane. o Footwall: The block below the fault plane. o Movement varies: hanging wall can move above or below footwall. B. Parts of Faults 1. Fault Plane: o Flat surface where rock movement occurs (can be vertical or sloping). 2. Fault Trace: o The line of intersection of the fault plane with the Earth’s surface. 3. Hanging Wall: o Upper side of a sloping fault plane. 4. Footwall: o Lower side of a sloping fault plane. 5. Additional Measurements: o Strike: Direction of the fault trace.  o Dip: Angle of the fault plane's slope. II. Types of Faults A. Normal Faults 1. Characteristics: o Hanging wall moves down relative to the footwall due to tensional forces. o Typically found in extensional environments (e.g., rift zones). 2. Stress and Strain: o Involves tensional stress that pulls crust apart and leads to elastic strain until brittle deformation occurs. B. Reverse Faults 1. Characteristics: o Hanging wall moves up relative to the footwall due to compressional forces. o Common in convergent boundaries (e.g., mountain ranges). 2. Stress and Strain: o Involves compressional stress causing shortening and thickening of the crust, leading to brittle deformation. C. Strike-Slip Faults 1. Characteristics: o Horizontal movement with little to no vertical displacement. o Common at transform boundaries (e.g., San Andreas Fault). 2. Types: o Sinistral (Left-Lateral): Opposite block moves left. o Dextral (Right-Lateral): Opposite block moves right. 3. Stress and Strain: o Driven by shear stress; involves horizontal shear strain. D. Oblique-Slip Faults 1. Characteristics: o Combine both horizontal (strike-slip) and vertical (dip-slip) movement. 2. Impact on Seismic Events: o Generate earthquakes with complex characteristics due to simultaneous shear and compressional stress. III. Mechanism of Fault Movement 1. Fault Movement: o Sudden or slow movement of rock blocks due to accumulated stress.  o Movement types: pulling apart (normal), pushing together (reverse), sliding past each other (strike-slip). 2. Tectonic Forces: o Compressional Forces: Push plates together (e.g., Himalayas). o Tensional Forces: Pull crust apart (e.g., East African Rift). o Shear Forces: Horizontal sliding of plates (e.g., San Andreas Fault). 3. Elastic Rebound Theory: o Describes energy accumulation and release during fault movement. C. Stick-Slip Behavior Stick Phase: Fault is locked; tension builds up from tectonic forces. Slip Phase: Fault slips when stress exceeds friction, releasing seismic waves. IV. Faults and Earthquake Generation Relationship Between Faults and Earthquakes: Earthquakes occur when stress is released along fault lines. Role of Fault Length and Depth: Deeper and longer faults can produce more powerful earthquakes. C. Case Studies of Major Earthquakes San Francisco Earthquake (1906): Demonstrated the impact of fault movement. New Madrid Seismic Zone (1811-1812): Unique large earthquakes away from tectonic plate boundaries. Haiti Earthquake (2010): Linked to the Enriquillo-Plantain Garden fault zone. V. Fault Zones and Seismic Hazard Assessment Identification of Active Faults: Use geological surveys, historical data, remote sensing, and paleoseismology. Fault Mapping and Monitoring: Utilize GIS, establish seismic networks, and conduct collaborative research. Zoning for Seismic Risk Management: Create seismic hazard maps, implement land use planning, and enforce building codes. D. Role of Faults in Earthquake Intensity and Frequency Magnitude and Frequency Relationship: Different faults yield different magnitudes and frequencies. Ground Shaking Intensity: Proximity to a fault influences ground shaking during earthquakes. Recurrence Intervals: Helps predict future events. VI. Faults and Infrastructure Impact on Buildings: Ground rupture can damage or collapse structures. Damage to Infrastructure: Fault movements can displace roads, collapse bridges, and disrupt utilities. Engineering Solutions: Implement base isolation, flexible design, and retrofitting. VII. Conclusion: Importance of Fault Studies Risk Identification: Pinpoints earthquake-prone areas. Seismic Design: Informs construction codes for safety. Ground Motion Understanding: Aids in foundation design. Mitigation Strategies: Guides retrofitting and emergency response planning. Monitoring Systems: Enhances early warning capabilities. Public Education: Promotes community awareness and preparedness.