Quiz 4 Flashcards
Nicolaus Steno
Danish physician, “Godfather of Stratigraphy”, created stratigraphic principles
Principle of Superposition
whatever on top is younger than what’s beneath it
Principle of Lateral Continuity
beds are deposited uniformly in lateral directions unless something is blocking them
Unconformities
Gaps in the rock record (missing periods of time)
What can cause unconformities?
Erosion (happening at a faster rate than deposition)
No deposition
Large changes in condition (like switching from an igneous environment to uplifting a sedimentary environment)
Types of unconformities
Disconformities
Angular unconformity
Nonconformity
Disconformity
Happens from missing deposition or erosion
Angular unconformity
Rocks are deformed (then eroded)
Nonconformity
Sedimentary rocks are deposited on top of igneous or metamorphic rocks
Faunal succession
The stratigraphic ordering of fossils
Desirable features of index fossils
Very common (chances of being buried are good)
Hard parts (good chances of fossilization)
Wide geographic range (correlation over a wide region is possible)
Lived in/deposited in different environments
Distinctive features (can be recognized from similar forms)
Short geological duration (few million years at most; provides a more specific age range)
Biostratigraphic correlation
Associating fossils and layerings of fossils to different time periods (and correlating that with different rock formations)
Good for determining a global relative time scale, but numerical/absolute time is still unresolved
Geochronology
Another name for numerical dating
Isotopes
A special chemical element having a different number of neutrons (but the same number of protons)
Stable isotopes
Non-radioactive isotopes that occur naturally
Radiogenic isotopes
Isotope that radioactively decays from an “unstable” parent to a “stable” daughter isotope
Natural uranium
High concentration of Uranium-238
Low-enriched, highly-enriched (and depleted, as a result of the enrichment process) deal with which isotope of uranium?
Uranium-235 (which has a shorter half-life than Uranium-238)
Low enriched uranium
Most commercial reactor fuel uses it
Highly enriched uranium
Used in naval propulsion reactors, nuclear weapons, and some research reactors
Alpha decay
Process where an unstable nucleus changes to another element by shooting out a particle of two protons and two neutrons
Beta decay
Decay in which a proton in a nucleus is converted to a neutron (after an electron is removed)
Isotopic dating
Gives the time a mineral cooled below its “closure temperature”
Cooling of magma or lava to solid in igneous rock
In metamorphic rock: dropping below closure temperature
Oldest crystal and rocks dated
Zircon crystals in Australia: 4.3 billion years
Oldest rock in Canada: 4.03 billion years
Radon
Produced by the radioactive decay of Ur and Th (one part of the long decay chain)
Emits alpha particles that damage human tissues
Radiocarbon dating (name what it is, what it uses, and what that element has a half life of)
Uses carbon-14 (living organisms keep it in equilibrium with the atmosphere until their death, when carbon-14 starts to decay to nitrogen-14)
Estimates the age of organic materials up until 62k years ago (as it has a half-life of 5730 years)
Other numerical dating techniques
Growth rings (trees and shells)
Rhythmic layering (annual layers in sediments or ice)
Evidence of plate tectonics (7 bits)
- Atlantic coastline/Gondwanaland
- Continental drift
- Fossil record (fossils spread across different continents that were once suggested)
- Geologic similarities
- Magnetism, magnetic reversals, magnetic stripes on the seafloor
- Topography of the Atlantic
- Seafloor spreading
Eduard Suess
Suggested the continents were once together as a supercontinent called “Gondwanaland” (1890s)
Alfred Wegener
Idea of continental drift in 1915
Other explanations for fossil record evidence
Rafting (across ocean)
Landbridges/Isthmian links
Island stepping stones
Wind currents
South America and Africa share what type of rock
Flood basalts, formed from a hotspot
Glacial striations
Marks where a glacier scratched bedrock
Magnetic stripes
Symmetric magnetic signals across what we know to be the mid-ocean ridge
Marie Tharp
Made maps showing the topography of the ocean; ridges and really deep trenches that pointed to plate locations
Proposed (the accepted idea) of plate tectonics
1965, J. Tuzo Wilson
Proposed the idea of seafloor spreading
1962: Harry Hess and Robert S. Dietz
Other folks later confirmed it in 1963
Divergent plates
Plates moving apart creates new lithosphere; occurs at mid-ocean ridges
Forms volcanoes
Shallower earthquakes
Convergent
Plates moving together causes them to collide, then pull one under the other, causing that plate to meet the mantle and be recycled
Forms volcanoes
Deeper earthquakes
Transform plates
Plates slide horizontally past each other, often happening in between divergent or convergent boundaries
No active volcano formation
Shallower earthquakes
Plate movement rate (at the outlier)
~15 - ~100 mm/year
Nazca plate: ~150 mm/year
Distance India moved (which has led to the formation of the Himalaya mountains, after the breakup of Pangaea)
3,300 km
T/F: plate tectonics has occurred for all of Earth’s history
False: only 85% of modern continental crust was present by the end of the Archean period
What causes plates to move?
Thought to be the convection of the mantle
Considerations to be made when installing a GPS station:
Attached to bedrock/hard rock (not susceptible to weathering/erosion beneath)
Be aware of biology around the station (which could lead to a noisy signal)
Put it in an area that’s interesting for scientific questions
Some things that GPS motion can help us understand
Plate motion, underground magma, changing glaciers and snow depth, compacting ground, changing amount of groundwater, size of lakes and reservoirs, amount of soil moisture, amount of water in the atmosphere, vegetation growth, amount of ash in atmosphere, sea level
If stations are moving in different directions, then to get the total displacement along the fault, you need to _________ their rates together
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