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Earth and Environmental Systems Objectives 9-10

Terms in this set (39)

9- Be able to reconstruct the geologic history of an area from a cross-section (using the principles of relative dating). In other words, know how to use the rules for relative dating.
1. Law of Original Horizontality - Most rocks laid down flat, and tilted only later during geologic events.
2. Law of Superposition - Oldest rocks are on the bottom.
3. Law of Lateral Continuity - Most rock beds don't end suddenly when originally laid down.
4. Cross-Cutting Relationships - A rock being cut by another rock/feature is older than that rock/feature.
5. Law of Inclusion - If rock A includes pieces of rock B, then rock B is older than rock A.
6. The law of Fossil Succession - fossil layers change in an ordered succession through time.
9- Know the various forms of "up indicators".
- Graded bedding: coarse on bottom, fine on top.
-Statragraphic separation (channel fill, cross-cedding)
-mud cracks
-raindrop impressions
-infilled voids
-Flute and Scrape (Casts & Molds)
-Vesicles at top of a lava flow
9- Fossil
A remnant, impression, or trace of an animal or plant of past geological ages that has been preserved within the Earth's crust.
9- Trace Fossil
Organism itself is not preserved, but evidence of it's existence is preserved.
9- Who was the person who developed the principle of fossil succession, where and when did he work, what did he do, and why else is he a famous geologist?
William Smith:
- early 1800's
-worked in England
-Recognized there was a pattern to the formation of fossils within different layers of earth.
-Different layers made at different times (deeper = older)
-was a surveyor
-first geologist to ever map an entire country
9- Index Fossils
A fossil where you can tell what part of geologic history a rock was formed in. (Organism could exist in many environments, but lived for a limited period of geologic history)
9- Ecological Indicator Fossil
A fossil where you can tell the environment that the rocks were formed in (Organism could only live in one type of environment, but existed for a long period of geologic history)
9- Know the definition of an unconformity, and the four types. Note: you will not be asked to identify one of these in the field, but can be asked about it on an exam.
Unconformity - a break in the stratigraphic rock record.
1. Angular unconformity.
2. Disconformity.
3. Nonconformity.
4. Paraconformity.
9- Be able to reproduce the Geologic Time Scale from memory.
Good luck (Key on Canvas)
9- What feature of life history marks the boundaries of periods?
Extinctions
9- What feature of life history marks the boundaries of eras?
Mass extinctions
9- Know the three types of radioactive emission and how or if they transmute one element into another.
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9- Understand the concept of a half-life (t1/2), and how it can be used to find the age of a rock/mineral. Be able to find the age of a rock given: parent to daughter ratio, and the half-life (t1/2) of the radioactive element in question.
-Half Life (T ½ ): Time for half of a population of parent atoms to decay to their daughter product.
-Assuming the isotope starts with 100% parent atoms, the percentage of parent atoms starts at 100%
-The FIRST half-life is at 50% parent atoms.
-Parent to Daughter ratio: parent atoms decrease as daughter products increase over time.
9- What assumptions are made in this "absolute dating" method?
1. Rock/Mineral system is closed
2. Initial ratio of parent to daughter must be determined
3. Half life must be constant through time
4. Measurements of parent and daughter must be accurate
5. A realistic value must be assigned to the daughter amount
9- What elements are useful for radiometric dating?
Uranium to Lead:
- U is an incompatible element concentrated in late-stage granitic crust.
- Long half life useful for measuring age of old continental rocks.

Rubidium to Strontium:
- Rubidium has the same charge and similar ionic radius as potassium.
-Good for dating K-Spar and micas in old continental crust.

Potassium to Agron:
-Potassium is abundant with a half life of 1.25 billion years.
-Must guard against argon loss (need closed system)

Carbon-14:
-Can date any YOUNG materials containing carbon
-Short half life, accurate to about 30,000 years.
9- What rock types are most and least useful for radiometric dating?
Sedimentary - Usually not possible to date
Metamorphic- Sometimes possible but requires caution
Igneous- Best Rock type for radiometric dating
9- What other physical aspect of a rock can be used to constrain its age.
Magnetic Reversals- Rocks were formed in an era where the Earth's magnetic field was reversed. Rocks "lock in" a magnetic field when they are formed.
9- How old are the oldest rocks and minerals in the world, and where do they come from
Rock: Acasta Gneiss from the Canadian Shield is 4.055 BILLION years old.
Mineral: A zircon crystal from Jack Hills of Western Australia is dated at 4.4 Ga. Gives evidence of water.
9- Where were the oldest fossils found, and how old are they?
3.5 Billion years old. Found in the Pilbara Craton of Western Australia
9- What is the oldest evidence of life and how old is it?
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10- What kind of rock is at the summit of Mt. Everest?
Limestone
10- What is the name of the person who came up with the theory of Continental Drift?
Alfred Wagner
10- What evidence was there for Continental Drift?
1.
2.
3.
4.
5.
10- What is the name of the giant supercontinent that Wegener postulated existed in the past, when do we believe it began to break apart, and what are the names of the two main pieces it broke into?
Pangaea
10- Why didn't the scientific community accept Continental Drift at the time it was proposed?
There was no explanation of a driving mechanism.
10- Who was the person who came up with the theory of sea-floor spreading and what was the initial evidence for this hypothesis?
Harry Hess:
- discovered ridges running along the center of ocean basins
- Flat-Topped sea mountains called "Guyots"
10- How old is the oldest oceanic crust, and how old is the oldest continental crust?
Oldest Ocean Crust- 170 Ma
Oldest Continental Crust- 4.055 Billion
10- Who wrote the famous paper that gave strong evidence for sea-floor spreading (and thus the mechanism for Continental Drift), and when was it written? What was the evidence given?
Vine and Matthews (1964)
Magnetic patterns on the sea floor convinced people of continental drift more than any previous evidence.
10- What are transform faults, and how were they used to further support sea-floor spreading?
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10- Be able to put into words the difference between Continental Drift and Plate Tectonics.
Continental Drift- Pangaea was broken and the continents spread apart. (Continents are moving)

Plate Tectonics- Earth is made up of multiple shifting plates (Continents and Oceans are moving)
10- What are the 7 major tectonic plates on the surface of the earth?
African, Antarctic, Eurasian, Indian-Australian, North American, Pacific, South American
10- What layer of the earth are the plates made of, and what is the layer of mobile earth beneath them called?
-Plates made from the Lithosphere
-Mobile Earth is the Upper Mantle (Asthenosphere)
-The boundary between the two layers of Earth is called the Mohorovicic Discontinuity
10- What are the three accepted mechanisms by which sea-floor spreading, and thus Plate Tectonics, is driven?
1. Conveyor-Belt movement of the Asthenosphere
2. Ridge Push (Gravity Sliding)
3. Slab Pull (Trench Suction)
10- Know the three types of plate boundaries, and the distinctive features of each (shape of the surface, types of earthquakes and volcanoes, what type of stress is most common at each, and the major fault type). Also, be able to distinguish between the three types of convergent boundaries.
Divergent:
- Linear ridge with a down-dropped valley at center.
- Fully developed always connects ocean crust to ocean crust
- Produces Basaltic lava and creates new sea floor
- Ridges connect around globe, largest mountain range on Earth
- Tension stress, normal faulting

Convergent:
-Characteristics depend on types of crust coming together
- ocean to ocean
- ocean to continental
- continental to continental

Conservative:
- Plates slide past each other (lithosphere not created/destroyed)
-Sheer stress causes deformation
- Broken and folded "melange"
-Frequent and strong Earthquakes
-example is san-andreas fault
Ocean-Ocean Convergence
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Ocean-Continent Convergence
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Continent-Continent Convergence
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10- What earth phenomenon do we use to measure the movement of plates? (If all plates are moving, what is the still point that we say they are moving relative to?)
-GPS used in the last 20 years
-Plates move relative to Mantle Plumes/Hotspots
10- Besides the above method of tracking plate movements, how else can we determine the position of plates in the geologic past?
Magnetic Inclination
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