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Questions and Answers
What is the longest division in the Geologic Time Scale?
Which principle suggests that rock layers are originally deposited horizontally?
What type of dating uses isotopic decay rates to assign specific ages to fossils?
Who is associated with the concept of Uniformitarianism?
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Which geochronologic unit is the shortest division of time?
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What is the primary use of index fossils in geology?
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Which method is used for dating organic materials up to approximately 70,000 years old?
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What time abbreviation represents 'billion years ago'?
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What is the primary challenge in using the Geological Time Scale for precise dating?
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Which layer of the Earth is primarily responsible for generating its magnetic field?
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Which of the following statements about the Earth's crust is correct?
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Which type of plate boundary results in mountain formation?
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What is the primary composition of the Earth's inner core?
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Which of the following supercontinents is known to have existed about 336-175 million years ago?
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How fast do tectonic plates typically move?
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What is a notable limitation of absolute dating methods?
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What marked the transition from the Paleozoic Era to the Mesozoic Era?
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During which period did the Cambrian Explosion occur?
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Which Epoch marks the current geological time?
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What event is associated with the emergence of early life on Earth?
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Which of the following is not a subdivision of the Cenozoic Era?
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What is the primary focus of age dating in geology?
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Which Eon does the Archean Eon immediately precede?
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What significant geological event occurred around 66 million years ago?
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What is the primary mechanism that leads to earthquakes at plate boundaries?
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Which type of fault is characterized by the hanging wall moving down relative to the footwall?
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Where do most earthquakes occur?
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What constitutes a fault in geological terms?
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What is the term for the upper side of a sloping fault plane?
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What type of tectonic plate movement is associated with reverse faults?
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In which tectonic setting are normal faults typically found?
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What is the term for the angle of the fault plane's slope?
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What type of fault is characterized by the hanging wall moving up relative to the footwall?
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Which type of fault movement is primarily associated with horizontal shear stress?
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What describes the 'stick-slip' behavior in fault movement?
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In what kind of boundary are reverse faults commonly found?
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What is the driving force behind oblique-slip faults?
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What typically leads to the generation of earthquakes along fault lines?
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Which of the following faults involves both lateral and vertical movement?
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What was significant about the San Francisco Earthquake of 1906?
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Study Notes
Geologic Time Scale (GTS)
- Divides Earth's history into eons, eras, periods, epochs, and ages based on life forms and events
- Eons are the longest divisions spanning billions of years
- Eras are within eons and last for hundreds of millions of years
- Periods are divisions within eras and last for tens to hundreds of millions of years
- Epochs are shorter than periods and last for tens of millions of years
- Ages are the shortest divisions, with some units even smaller
- GTS is based on stratigraphy and fossil records
- Fossils mark beginnings and ends of time intervals
Principles Behind GTS
- Nicholas Steno's principles:
- Superposition: Bottom layer is oldest
- Horizontality: Layers were originally horizontal
- Original Lateral Continuity: Layers extend until interrupted by other rock layers
- Historical contributions:
- Abraham Gottlob Werner: All rocks originated in oceans
- James Hutton: "Uniformitarianism" (present processes explain the past)
- William Smith: The principle of Biologic succession (unique fossils identify specific time periods)
- Charles Lyell: The principle of cross-cutting relationships and Inclusion principle
- Charles Darwin: Theory of natural selection as a mechanism of evolution
Methods of Determining Fossil Age
- Relative Age Dating: Uses layer positions for sequence dating
- Relative Dating with Index Fossils: Widespread, short-lived fossils help correlate layers
- Absolute Age Dating: Uses isotopic decay rates to assign specific ages
- Radiocarbon Dating: Carbon-14 decay for organic materials up to ~70,000 years old
- Uranium-Lead Dating: Uranium isotopes Effective for igneous rocks, millions to billions of years old
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
- 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)
- Paleogene Period (66 to 23 million years ago)
- Paleocene (66 to 56 million years ago)
- Eocene (56 to 34 million years ago)
- Oligocene (34 to 23 million years ago)
- Neogene Period (23 to 2.6 million years ago)
- Miocene (23 to 5 million years ago)
- Pliocene (5 million years ago to 2.6 million years ago)
- Quaternary Period (2.6 million years ago to present)
- Pleistocene Epoch (2.6 MYA to 10,000 years ago)
- Holocene Epoch (10,000 years ago to present)
- Paleogene Period (66 to 23 million years ago)
Earth’s Timeline and Geological Events
- 4.6 Billion Years Ago: Formation of Earth; initial molten state; moon formation stabilized tilt
- 4.0 – 2.5 Billion Years Ago: Cooling, oceans formed; emergence of early life (cyanobacteria), triggering the Great Oxygenation Event
- 541 – 245 Million Years Ago: Cambrian Explosion; diversification of life and hard-shelled invertebrates
- 245 – 66 Million Years Ago: Age of Reptiles and Dinosaurs; dominance of dinosaurs and existence of Pangea
- 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
- Age Dating: Determines ages of rocks, fossils, and geological formations
- Correlation of Rock Strata: Reconstructs Earth’s history and geological relationships
- Resource Exploration: Guides exploration in petroleum, mineral, and mining industries
- Climate Change Studies: Analyzes past climate conditions and mechanisms
- Evolutionary Biology: Understands development of life and interspecies connections
- Archaeology: Ages archaeological sites and artifacts for cultural evolution studies
Limitations and Criticisms of the Geological Time Scale
- Incomplete Fossil Record: Gaps in fossils make precise dating difficult
- Assumptions About Rates of Change: Based on assumptions that can be challenged and revised
- Dating Techniques: Absolute dating methods have limitations and sources of error
- Conflicting Interpretations: Different scientific interpretations can lead to disagreements about timing and relationships
- Controversies: Disagreements exist regarding mass extinctions and origins of species
Earth Structure
- Layers: Earth is divided into the crust, mantle, outer core, and inner core, each with unique compositions and characteristics
- 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
- 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)
- Lithosphere: Solid, outer part of Earth
- Asthenosphere: Denser, weaker layer beneath the lithospheric mantle
- Lower Mantle: Solid, contributes to heat transfer within Earth
- Outer Core: Liquid layer made of iron and nickel; generates Earth’s magnetic field
- Inner Core: Solid, high-pressure iron and nickel core at Earth’s center
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
- 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.
- 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)
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:
- Tectonic plates meet and get "stuck," building stress
- When stress exceeds strength, plates slip, releasing energy as seismic waves
- Fault Types:
- Reverse Fault: Compression at convergent boundaries
- Normal Fault: Extension at divergent boundaries
- Strike-Slip Fault: Horizontal sliding at transform boundaries
- Impact: Earthquakes can shake, crack, and displace the ground, affecting infrastructure and safety
Definition of Faults
- Earth's Crust Composition: Made of tectonic plates (7 major: African, Antarctic, Eurasian, Indo-Australian, North American, Pacific, South American)
- Plates move due to convection currents in the mantle.
- Plate Boundaries: The meeting point of two tectonic plates where faults form
- Faults accommodate plate movement and can cause earthquakes.
- Definition of Fault: A crack or fracture in the Earth's crust where rocks have moved or been offset
- Ranges from microscopic cracks to large fault systems
- Components of Fault:
- Hanging Wall: The block above the fault plane
- Footwall: The block below the fault plane
- Movement varies: hanging wall can move above or below footwall
Parts of Faults
- Fault Plane: Flat surface where rock movement occurs (can be vertical or sloping)
- Fault Trace: The line of intersection of the fault plane with the Earth’s surface
- Hanging Wall: Upper side of a sloping fault plane
- Footwall: Lower side of a sloping fault plane
- Additional Measurements:
- Strike: Direction of the fault trace.
- Dip: Angle of the fault plane's slope
Types of Faults
- Normal Faults:
- Hanging wall moves down relative to the footwall due to tensional forces
- Typically found in extensional environments (e.g., rift zones)
- Reverse Faults:
- Hanging wall moves up relative to the footwall due to compressional forces
- Common in convergent boundaries (e.g., mountain ranges)
- Strike-Slip Faults:
- Horizontal movement with little to no vertical displacement
- Common at transform boundaries (e.g., San Andreas Fault)
- Types:
- Sinistral (Left-Lateral): Opposite block moves left
- Dextral (Right-Lateral): Opposite block moves right
- Oblique-Slip Faults:
- Combine both horizontal (strike-slip) and vertical (dip-slip) movement
- Generate earthquakes with complex characteristics due to simultaneous shear and compressional stress
Mechanism of Fault Movement
- Fault Movement: Sudden or slow movement of rock blocks due to accumulated stress
- Movement types: pulling apart (normal), pushing together (reverse), sliding past each other (strike-slip)
- Tectonic Forces:
- Compressional Forces: Push plates together
- Tensional Forces: Pull crust apart
- Shear Forces: Horizontal sliding of plates
- Elastic Rebound Theory: Describes energy accumulation and release during fault movement
- Stick Phase: Fault is locked; tension builds up from tectonic forces
- Slip Phase: Fault slips when stress exceeds friction, releasing seismic waves
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
- 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
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Description
Explore the Geologic Time Scale (GTS) which divides Earth's history into eons, eras, periods, epochs, and ages based on life forms and significant events. Learn about the principles of stratigraphy that help establish these divisions, as well as the historical contributions of key figures in geology. Test your knowledge on the key concepts and terms related to GTS.
