ERS103H5 Study Guide - Final Guide: Cambrian Explosion, Snowball Earth, Continental Crust
ERS103 Exam Review
Klaudia Pechera
Lecture 1 – Geology Overview
• Igneous – melted rock
• Metamorphic – deformed rocks
• Sedimentary – deposited rock
• Cryosphere: glaciers, terrestrial ice sheets, sea ice
• Hydrosphere: Ocean circulation driven, in part, by atmospheric circulation
• Asthenosphere: slushy-mantle 100-200km
Relative vs. Absolute Dating
• Relative
o Steno’s 3 principles
▪ Principle of Superposition: sedimentary layers are deposited in a time sequence, oldest on
the bottom youngest on the top
▪ Principle of Original Horizontality: layers of sediment are originally deposited horizontally
under the action of gravity
▪ Principle of Lateral Continuity: layers of sediment initially extend laterally in all
directions; laterally continuous
o Index fossils: small size, abundant/large samples, easy to identify, good preservation, narrow
stratigraphic range
▪ Radiometric Dating
Geological Timescale
• 4 Eons, 10 Eras, 12 Periods
o Hadean: 4.5-Ga-4.0Ga → Formation of the Earth
o Archean: 4.0Ga-2.4Ga → Oldest rocks, oldest life
o Proterozoic: 2.3Ga-541Ma → Rise of oxygen & complex life
▪ Neoprotezoic: Snowball Earth and Ediacara biota
• Ericaran: oldest multicellular animals
o Phanerozoic: 541Ma-Present → Rise of complex animals
▪ Paleozoic: age of fish
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• Cambrian: Cambrian explosion
• Ordovician: Major diversification of marine invertebrates
• Silurian: First vascular plants
• Devonian: First trees, insects, diversification of fish
• Carboniferous: Vat coal-forming swamps, first reptiles
• Permian: Supercontinent Pangea, largest mass-extinction
▪ Mesozoic: age of dinosaurs
• Triassic: First dinosaurs
• Jurassic: First birds
• Cretaceous: First flowering plants, extinction of dinosaurs
▪ Cenozoic: age of mammals
• Paleogene: Modern mammals and first grasses
• Neogene: First humans
Relative vs. Absolute Dating
• Relative:
o Steno’s 3 Principles (DRAW UNDERNEATH)
▪ 1) Principle of Superposition: Sedimentary layers are deposited in a time sequence, with
the oldest on the bottom, youngest on the top
▪ 2) Principle of Original Horizontality: layers of sediment are originally deposited
horizontally under the action of gravity
▪ 3) Principle of Lateral Continuity: layers of sediment initially extend laterally through all
directions they are laterally continuous
o Index Fossils: a fossil that is used for dating and correlating the strata which is found
▪ Characteristics of an Index Fossil: small, abundant/large sample size, easy to identify,
good preservation
• Absolute:
o Measures decay of radioactive isotopes – isotopes of an element have nuclei with same protons
different neutrons
o Requirements of Absolute Dating
▪ 1) The half-life of the parent isotope must be appropriate length of the period to be dated
▪ 2) The initial concentration of the isotope must be known/found
▪ 3) There must be a connection between the event being dated and the start of the
radioactive decay clock
How do we study the Inside of the Earth? Seismic Waves
• Primary Waves (P-waves): compressional waves, much faster than s-waves, and travel through all materials
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• Secondary Waves (S-waves): shear waves, travels only through solids (accordion like)
o P and S waves are used to study the inside of the Earth through its velocity – s waves disappears
within the outer core and reappears in the inner core, and since s waes only appear through solids
it is hypothesized that the outer core is liquid
o P-wave and S-wave shadow zones
Structure of the Earth
Moho: boundary between a slower velocity zone above, and
a faster velocity zone below – between continental crust
and mantle
Lithosphere: hard, rigid portion of the Earth – composed of
the crust and upper mantle
Asthenosphere: below the lithosphere
Low-velocity Zone: compared to lithosphere and remainder
of the mantle
Earth’s Magnetic Field: Benefits
• Navigation
• Protection
Pangea: Hypothesized by Alfred Wegener
• Evidence: Glaciers
o Distribution of Permian glacial deposits and striations – Gondwana
• Climate Belts
o Late Palaeozoic rocks preserved show evidence of ancient climate belts
o Climate belts – align in a sensible matter – fits as if it were Pangea
• Fossil Distribution
o Creatures could not migrate across the ocean, and the distribution within different continents
explains Pangea
• Mountain Belts
o Fit as if it were separated through the continental drift
• Plate Tectonics
o Paleomagnetism – polar wander
▪ Problems with Polar Wander: the apparent polar wandering path demonstrates that the
continents, not the poles, wandered through time
o Sea-floor spreading – magnetic reversals, earthquakes
▪ Sonar: based on the travel time of sound generated off a ship then reflected off the bottom
of the sea floor
▪ Bathmetry: sonar allows the ship to easily measure sea-floor
o Deep-sea drilling – sediment thickness
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