Final Cheat Sheet - ERTH 209

Stratigraphy and Geological Time

Steno’s Principles of Stratigraphy

  • Principle of Layer Superposition: In undisturbed strata, the oldest layer is at the bottom and the youngest at the top.

  • Principle of Layer Successive Formation: A layer’s formation occurs without the existence of layers above it.

  • Principle of Original Layer Horizontality: Sedimentary layers are originally deposited horizontally; inclined layers indicate crustal disturbances.

  • Principle of Lateral Layer Continuity: Layers extend laterally until they thin out or meet a barrier.

Layer Terminations

  • 1774: First scientific estimate of Earth’s age (~70,000 years), challenging creationist perspectives and laying groundwork for modern geochronology.

Interpreting Stratigraphical Successions

  • Sedimentological Data: Structures like mudcracks and ripple marks help determine original depositional environments.

  • Normal Succession: Younger layers are situated atop older layers.

  • Inverted Succession: Tectonic forces can disrupt typical layering.

Relative Ages by Superposition

  • Relative Ages: Layers in different sections can be correlated to determine their relative chronological order.

  • Contributions to Geology:

    • Nicolaus Steno: Established principles of stratigraphy.

    • John Strachey: Investigated layer terminations.

    • Georges Louis Leclerc (de Buffon): Advanced understanding of Earth's age.

    • Tomaso d’Arduinio: Emphasized sedimentary structures.

    • Sir William Smith: Pioneered fossil-based correlation and geological mapping (first geological map of England, dubbed "the map that changed the world").

    • Sir Charles Lyell: Formulated principles for dating igneous and metamorphic rocks.

Fossil Ranges

  • Fossils serve as chronological markers for stratigraphic correlation.

  • Index Fossils: Layers with identical fossils can be matched across different regions.

Sir Charles Lyell’s Principles

  • Principle of Inclusions: The rock containing inclusions is younger than the absorbed fragments.

  • Principle of Cross-Cutting Relations: Features such as dikes are younger than the surrounding rocks they intersect.

  • Relative Ages of Lava Flows: Lava flows bake the underlying layers; younger sills can bake both layers above and below.

Radioactive Decay

  • Radioactive Decay: Unstable isotopes transform into stable daughter isotopes over time.

  • Decay Series: For example, Uranium-238 decays to Lead-206 through alpha and beta decay steps.

  • Half-Life: The duration it takes for half the parent isotope to decay into a daughter isotope; is crucial for precise dating.

Geological Time Summary

  • Relative Geological Time Scale: Stratigraphy organizes layers and fossils chronologically.

  • Eons of Earth’s History:

    • Hadean: Formation of Earth; no rock record.

    • Archean: Earliest rocks and fossils.

    • Proterozoic: Includes microscopic and macroscopic fossils.

    • Phanerozoic: Contains visible fossils; divided into Paleozoic, Mesozoic, and Cenozoic eras.

Phanerozoic Eon

  • Paleozoic Era: Comprised of periods such as Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian (or Carboniferous), and Permian.

  • Mesozoic Era: Includes Triassic, Jurassic, and Cretaceous periods; marked by significant extinction events including the Permian/Triassic crisis and Cretaceous/Paleogene impact.

  • Cenozoic Era: Encompasses the Paleogene, Neogene, and Quaternary periods; fossils closely resemble modern organisms.

Fossil Record

What are Fossils?

  • Definition: Remains of ancient life forms; derived from Latin meaning "to be dug out from the Earth," a term coined during the Renaissance.

  • Historical Context: Initially encompassed both minerals and vestiges of life forms.

Fossil Classifications

  1. By Age:

    • Fossils older than 11,700 years.

    • Subfossils younger than 11,700 years (not all considered fossils).

  2. By Nature:

    • Body Fossils: Preserve parts of the organism.

    • Trace Fossils: Indicate organism activities (e.g., movement traces).

    • Chemical Fossils: Preserve only small organic components.

Examples of Fossils

  • Body Fossils:

    • Stony coral, Cephalopod shells, Trilobite, Belemnites.

  • Trace Fossils:

    • Cruziana (movement trace), Skolithos (vertical galleries), Acanthotheuthis (movement trace of belemnite).

  • Mixed Fossils:

    • Mesolimulus (horseshoe crab) with movement traces.

Historical Context

  • Pre-scientific Understanding: Knowledge of fossils existed in early Antiquity; e.g., brachiopod fossil from King Senwosret I’s time (Middle Kingdom, Egypt).

  • First Scientific Report:

    • Xenophanes of Colophon (~570-475 B.C.) described marine fossils found inland, indicating past interactions between land and sea.

Fossilization Process

  • Overview: Transformation of dead organisms into fossils; selective process with a high destructive nature.

  • Conditions for Fossilization:

    • Rapid Burial: Sudden events (landslides) or increased sedimentation rates.

    • Anoxic Conditions: Minimized decay, thereby enhancing preservation.

Types of Fossilization

  1. Casual Fossilization:

    • Petrification/Lithification/Permineralization: Transformation into stone; pores filled with minerals (e.g., Psaronius).

    • Recrystallization: Conversion of one mineral to another (e.g., aragonite to calcite).

    • Carbonization: Loss of elements during decay, leaving only carbon (e.g., Pecopteris).

    • Impressions: Formed by the organism’s weight in sediment (e.g., Pecopteris leaf).

  2. High-Quality Fossilization:

    • Amber: Fossilized tree resin (e.g., Plesiomyrex).

    • Tar Pits: Hydrocarbon swamps preserving organisms (e.g., Cybister).

    • Congealment and Dehydration: Essential for preserving soft tissues.

Fossil Lagerstätten

  • Sites known for exceptional fossil preservation including soft tissues.

  • Examples:

    • Burgess Shale (Canada): Middle Cambrian fossils like Ottoia.

    • Chengjiang Fauna (China): Lower Cambrian fossils like Haikouichthys.

Life Emergence on Earth and Early Evolution

CHON Elements

  • Dominant elements in life forms today: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N); Sulfur and phosphorus present in smaller amounts.

Earth’s Early Atmosphere

  • Alexandr Ivanovic Oparin's Hypothesis: CHON molecules could form in early conditions, leading to the first cells.

  • Original atmosphere: Reducing, minimal free molecular oxygen allowed CHON compounds to accumulate; primordial soup was lifeless.

Isua Supercrustal Group

  • Location: Greenland; contains some of Earth's oldest sedimentary rocks (3.8–3.7 billion years old).

  • Indicators of organic origins include rare oxides, carbonates, and significant graphite levels.

    • Demonstrated that basic elements could chemically react to form organic CHON molecules, producing essential amino acids.

Experimental Confirmation: Miller-Urey Experiment (1953)

  • Polymerization Process: Formation of larger molecules (polymers) from simple CHON structures; e.g., cellulose is formed from repeating glucose units.

Evidence of Isolated Cells

  • Early Archean Evidence: From the Pilbara Craton (Apex Chert), shows evidence of bacteria and cyanobacteria debris.

    • Examples include folded filament structures and chain-like structures resembling modern bacteria.

Stromatolites

  • Fossilized microbial structures with growth surfaces hosting photosynthetic cyanobacteria; organized layers from surface to center clarify oxygen-depleting zones.

Banded Iron Formation (BIF)

  • Composed of alternating layers of iron oxides and cherts/jaspers; displays reddish and green/grey colors related to iron content.

Oldest Eukaryotes

  • Biomarkers: Chemical fossils aged between 2.1–1.8 billion years.

    • Bitter Springs Formation shows isolated eukaryote cells (1 billion years old) such as algae with preserved cellular division.

Eukaryote Examples

  1. Bangiomorpha: Resembles modern red algae; ~1.2 billion years old.

  2. Torridonophycus: Escaped from a bag-like structure; adapted to harsh climates; ~0.9 billion years old.

  3. Melanocyrillium: Resembles testate amoebas; ~0.8–0.9 billion years old.

Dinosaurs

Vertebrate Evolution

  • Vertebrates evolved from chordates in the Lower Cambrian; early forms included jawless fishes and jawed fishes.

  • Key Examples:

    • Haikouichthys: Earliest vertebrate.

    • Sacabambaspis: An agnathan with a cephalic shield.

Fishes

  • Aquatic organisms with jaws that evolved in the Middle Silurian; colonized diverse environments with either bony or cartilaginous skeletons.

  • Dunkleosteus: A dominant predator in marine ecosystems.

Amphibians

  • Adapted to land with:

    1. Dual respiration: lungs and skin (dependent on moisture).

    2. Aquatic reproduction: numerous unprotected eggs.

Reptiles

  • Evolved from amphibians, exhibiting adaptations for terrestrial life, including shelled eggs and reduced dependency on water.

  • Key Examples: Diapsids like Hylonomus.

Synapsid Reptiles

  • Dominated Late Paleozoic to Early Triassic; examples include Dimetrodon (predator) and Edaphosaurus (herbivore).

Diapsid Takeover and Dinosaur Origins

  • Dinosaurs evolved from diapsid reptiles during the Upper Triassic,

    • Early dinosaurs were small bipedal or quadrupedal insectivores or carnivores, possibly originating in South America.

    • Herrerasaurus: Example of early dinosaurs.

Dinosaur Classification

  • Based on pelvic structure:

    1. Saurischians: Lizard-hipped, pubis points down/forward.

    2. Ornithischians: Bird-hipped, pubis points backward.

Theropods

  • Bipedal predators characterized by knife-like teeth and hollow bones.

  • Key Examples:

    • Allosaurs: Apex predator of Jurassic and Cretaceous eras.

    • Tyrannosaurs: Notable apex predator (e.g., Tyrannosaurus Rex).

Sauropodomorpha

  • Early large dinosaurs evolving into quadrupedal giants:

    • Plateosaurus: Prosauropod from Upper Triassic.

    • Ultrasaurus: Large sauropod from Upper Jurassic.

Ornithischians

  • Herbivorous dinosaurs with unique adaptations:

    • Stegosaurs: Have beak-like structures for plant consumption.

    • Ankylosaurs: Armored with fused osteoderms.

    • Ceratopsians: Horned dinosaurs, such as Triceratops.

Evolution of Flight

  • Pterosauria: Winged reptiles from Upper Triassic to Cretaceous, evidence of active flight.

    • Examples:

      • Rhamphorhynchus: Upper Jurassic pterosaur.

      • Pteranodon: Late Cretaceous flying reptile.

Avian Evolution

  • Birds evolved from theropods during the Late Mesozoic; hypotheses on flight origin include arboreal (gliding) and cursorial (flapping during ground running).

Plate Tectonics

Lithospheric Plates

  • Major Plates: Seven main plates (e.g., North American, Pacific) comprise oceanic and continental lithosphere.

  • Pacific Plate: Entirely oceanic; covers the Pacific Ocean area.

  • Minor Plates: Fragments of major plates, evolving independently.

Key Discoveries

  • Alfred Wegener: Proposed "continental drift" (1915), citing geological similarities across continents (e.g., South America & Africa).

  • Gondwana Supercontinent: Identified by Eduard Suess using fossil evidence.

  • Wegener's hypothesis was initially rejected due to lack of a clear mechanism.

Oceanic Floor Features

  • Abyssal Plains: Flat regions at depths of 4-4.5 km.

  • Mid-Oceanic Ridges: Underwater mountain chains with volcanic activity.

  • Oceanic Trenches: Deepest areas, often secondary to earthquakes.

  • Seamounts: Volcanic underwater mountains.

  • Island Arcs: Chains of volcanic islands parallel to trenches.

Tectonic Regimes

  1. Divergent: Plates separating; characterized by volcanic activity (e.g., Mid-Atlantic Ridge).

    • Stages from continental rift to mature oceans.

  2. Convergent: Plates colliding, creating subduction zones or mountain ranges.

    • Types include ocean-ocean, ocean-continent, and continent-continent convergence.

  3. Transform: Plates slide past each other (e.g., San Andreas Fault).

Wilson Cycle

  • Describes the progression of ocean formation, expansion, and closure, originating from the breakup of Pangea during the Mesozoic.

North American Plate

  • Bordered by several major and minor plates (e.g., Pacific, Juan de Fuca).

  • Formed during the breakup of Rodinia in the Proterozoic Era; includes stable cratonal components and deformed sections.

Key Observations

  • Seafloor Age: Younger at mid-oceanic ridges; older towards continents.

  • Magnetic Stripes: Correlating with mid-oceanic ridges; confirming seafloor spreading.

  • Earthquakes/Volcanism: Often concentrated at plate boundaries.

Latin Names – Structurally Organized with Definitions & Periods

Early Life and Fossils

  • Cryptozoon: Evidence of early life forms in Precambrian stromatolitic structures.

  • Bangiomorpha: Earliest known eukaryote (~1.2 billion years).

  • Torridonophycus: Resilient algal microstructures; Late Proterozoic.

  • Melanocyrillium: Early eukaryotic forms (~0.8-0.9 billion years).

Early Vertebrates

  • Haikouichthys: Earliest vertebrate with primitive features.

  • Sacabambaspis: Early jawless vertebrate highlighting evolutionary stages.

  • Dunkleosteus: A large prehistoric placoderm predator.

Reptilian Evolution

  • Hylonomus: First true reptile, a diapsid from the Late Carboniferous.

  • Mesosaurus: Early aquatic reptile key to continental drift evidence.

  • Edaphosaurus & Dimetrodon: Significant pelycosaurs with adaptations for survival.

Dinosaurs

  • Early Dinosaurs:

    • Herrerasaurus: One of the oldest known dinosaurs from the Late Triassic.

  • Theropods:

    • Allosaurus: Dominant predator of Jurassic/Cretaceous.

    • Tyrannosaurus: Apex predator of the Cretaceous, likely originated in Asia.

  • Sauropodomorphs:

    • Plateosaurus & Ultrasaurus: Notable examples of large dinosaurs.

  • Ornithischians:

    • Stegosaurus, Ankylosaurus, & Triceratops: Examples of herbivorous dinosaurs with unique adaptations.

Flying Reptiles

  • Sordes & Pteranodon: Evidence of adaptations for flight in the late Mesozoic.

Evolution of Birds

  • Rhamphorhynchus & Archaeopteryx: Key species in understanding the origin of avian flight.