Geology Review 12&13
Rhythmic layering
Layering that develops due to seasonal changes in sedimentary accumulations and glacier ice
Fission Track
Line formed by the ejection of an atomic particle during the decay of a radioactive isotope which damages the crystal
Describe two different methods of correlating rock units. How was correlation used to develop the geologic column? What is a stratigraphic formation?
Over broad areas fossil correlation is used, because sources of sediments and depositional environments may change from one location to another. Sediment may look very different, but can still be the same age. Lithologic correlation is where geologists correlate formations between nearby regions based on similarities in rock type. Correlating helped form geologic column by allowing geologists to compare rocks at millions of different places, which helped create the composite stratigraphic column Stratigraphic formation is a sequence of bed of a specific rock type that can be traced over a broad region
What does the process of radioactive decay entail?
Parent isotopes are changing into daughter isotopes.
Uniformitarianism
Physical processes we observe today also operated in the past at roughly the same rate
Salt is a mineral, but the plastic making up an inexpensive pen is not. Why not?
Plastic is man-made, while salt is found in nature
Geologic map
Portrays the spatial distribution of rock units at the Earth's surface
What is the prime characteristic that geologists use separate minerals into classes?
Principal anion or anion group
Isotopic Dating
Process of determining the numerical age of racks
How do Geologists obtain an isotopic date? What are some of the pitfalls in obtaining a reliable one?
Radioactive elements decay at a constant rate over time, and they can be measured by comparing the parent isotope with the daughter isotope. Pitfalls:
Carbon-14
Radioactive isotope of carbon that naturally in the atmosphere when cosmic rays bombard atmospheric nitrogen 14
Craton
Region of old and relatively stable continental crust
Correlation
Relationship between the strata at on locality and strata of another
Compare numerical and and relative age
Relative age is the age of a formation with respect to another formation. Numerical age is actual age of a feature in years.
Fossil
Remnants of once living organisms in sediment
On what basis do mineralogists organize silicate minerals into distinct groups?
The arrangement of the silica tetrahedron
Nonconformity
The boundary between an old sequence of sediment, and new sequence.
What may have caused the flooding during the Cretaceous PEriod
The cretaceous mid-ocean ridges occupied more volume than today due to shallow depth
Phanerozoic Eon
The last 542 Million years of earth's history. Appearance of hard shelled organisms
Why can't we date sedimentary rocks directly
The mineral component of sedimentary rocks are generally older than the rock itself (Inclusion_
How did the atmosphere and tectonic conditions change during the Proterozoic Eon?
The plates went from small and fast moving to large and slow moving. Oxygen become abundant
Geologic time
The span of time since Earth's formation
How are growth rings and ice cores useful in determining the ages of geologic events?
They can help determine how long an organism survived. Ice cores can keep track of what the climate was like, and the temperatures.
Describe the principles that allow us to determine relative ages of geologic events
Uniformitarianism- Physical processes we observe today also happened in the past at roughly the same rate. Original horizontality- Sediments on Earth settle out of a fluid in a gravitational field Superposition- Each layer must be younger than the one below it in a sequence of sedimentary rocks
How does the principle of fossil succession allow us to determine the relative age of strata
We can say one bed is older than another bed based on the fossils found within them
How do you distinguish cleavage surfaces from crystal faces on a mineral?
Cleavage planes tend to be smooth and shiny, while crystal faces are not.
List and define the principal physical properties used to identify a mineral
Color, streak, luster, density, hardness, special properties, breakage(fracture/cleavage),
Geologic Column
Composite stratigraphic column of Earth's history
Pleistocene ice age
Continental glaciers expanded and retreated across northern continents around 20 times during the Quaternary Period
Radioactive decay
Converts isotopes into a different element
Describe the condition of the crust, atmosphere, and oceans during the Hadean Eon
Crust was liquid, atmosphere was composed of dangerous chemicals such as methane, carbon, sulfur
Daughter isotope
Decay product
Isotope
Different versions of an element
Stromatolite
Distinctive mounds of sediment produced by mats of cyanobacteria
Era
Division of Eon
Epoch
Division of Period
Period
Division of era
Why are there no whole rocks on Earth that yield isotopic dates older than 4 Ga?
During Hadean Eon, no rocks were present, Earth's surface was liquid
Hadean Eon
Earth bombarded by planetesimals, very hot, dangerous gases in the amosphere.
Proterozoic Eon
Earth went from small fast moving plates and low oxygen to large, slow moving continents, and huge amounts of oxygen
What are the major organisms that appeared during the Paleozoic?
Eel like organisms, shelled organisms that became more complex, vertebrae animals, plantkton
Why do some minerals occur as euhedral crystals, whereas others occur as anhedral grains?
Euheral crystals have well formed crystal faces(Geodes), Anhedral grains don't have well formed crystal faces
Superplume
Extremely active mantle plumes
Angular unconformity
Formed where rocks were tilted by folding or faulting before being exposed to Earth's surface
Describe srveral ways that mineral crystals can form
Freezing of a liquid, precipitation from a solution, solid-state diffusion(movement of atoms through a solid), interfaces between the physical and biological Earth System though biomineralization, and precipitation directly from gas (volcanic vents, geysers)
Why is glass not a mineral?
Glass is not crystalline in structure
Differentiation
Gravity pulling iron toward the center of the earth
Precambrian
Hadean, Archean, and Proterozoic
Half-life
How long it takes for half of a group of parent isotopes to decay
What major climatic and biologic events happened during the Pleistocene?
Ice age
Cross-cutting relations
If one geologic feature cuts across another, the feature that has been cut is older
Superposition
In a sequence of sedimentary rock layers, each layer must be younger than the one below
Parent isotope
Isotope that undergoes decay
How did the Cambrian explosion of life change the nature of the living world?
It was a huge diversification of life. Earth went from inhabited to habited really quicly by many differetnt organisms
Phanerozoic
Last 542 Million years of Earths history
Proterozoic Eon
2 Ga- 542 Ma
Great oxygenation event
2.4 Ga, photosynthetic organisms thrived, and there was a buildup of oxygen, because the plants had enough oxygen. The oxygen built up in the atmosphere. Created Banded Iron Formations (BIFs)
End Triassic
200 Ma
End Permian
251 Ma
Archean Eon
3.85-2.5 Ga
Late Devonian
375 Ma
What is the age of the oldest rocks on Earth? What is the age of the oldest rocks known? Why is there a difference?
4.03 Ga, 4.57 Ga. They come off of different planets, so they can e older than Earth rocks
End Ordovician
444 Ma
End Cretaceous
66 Ma
Eon
A major division of geologic time
What is a mineral, as geologists understand the term?
A mineral is a naturally occurring solid, formed by geologic processes, that has a crystalline structure and a definable chemical composition
Stratigraphic formation
A sequence of beds of a specific rock type that can be traced over a fairly broad region
Unconformity
A surface that represents a period of non-deposition and possibly erosion
What continents formed as a result of the breakup of Pangaea
Africa, South America, Antarctica, and Australia
Numerical age
Age of a feature in years
Relative age
Age of one feature with respect to another in a sequence
How does an unconformity develop? Describe the differences among the three kids of unconformities.
Angular unconformity- Formed when rocks were tilted by folding or faulting before being exposed at the Earth's surface. Disconformity- Beds of rock parallel to each other, but have a measureable age difference between them Nonconformities- Happens when sedimentary strata \are deposited on top of crystalline (metamorphic or igneous) rock
Disconformity
Beds of the rock sequence above and below the unconformity are parallel to one another, but there is a measurable age difference between the two sequences. The disconformity surface represents a period of nondeposition and/or erosion
Hadean Eon
Birth of Earth-3.85 Ga
Contact
Boundary surface between two formations
Shield
Broad, low lying area in which basement older than about 1 Ga is exposed in abundant surface outcrops
How can you determine the hardness of a mineral? What is the Mohs hardness scale?
By comparing it to other minerals. By using the Mohs hardness scale, you compare the hardness of a mineral to common items.
What evidence do we have that Earth nearly frozeover twice during the proterozoic eon?
By finding glacial sediments in places worldwide in the stratigraphic sequence
Stratigraphic column
Summarization about the sequence of sedimentary strata at a location
What life forms appeared during the Mesozoic?
Swimming reptiles, coral, flying reptiles, dinosaurs
Closure temperature
Temperature where isotopes are no longer free to move
geologic time scale
Numerical ages of periods and eras in the geologic column
Cratonic platform
Occupies the Midwest and high plains of the U.S
Fossil succession
Once a fossil species disappears at a horizon in a sequence of strata it never reappears higher in the sequence. Extinction is forever.
What could have caused the K-T Extinctions?
The 14 km meteorite
Index Fossils
Species' that existed for a short interval of the geologic column, and are found in a specific time interval
Stratigraphic sequence
Strata deposited on the continentduring periods when continents were submerged
Magnetostratigraphy
Study of comparing the pattern of the reversals in a sequence of strata with the pattern of reversals in a reference column. Helps determine age of a sequence
Cambrian Explosion
Major diversification of life
Pangaea
Result of a succession of continental collisions
Growth rings
Rings that form due to seasonal changes. Happens in trees, travertine deposits, and shelly organisms
What major tectonic provinces formed in the western United States during the Cenozoic?
Rocky Mountains
Original Horizontalty
Sediments on Earth settle out of a fluid in a gravitational field
Geochronology
Study of numerical ages
Archean Eon
Substantial amounts of crustal rocks formed
Cambrian Explosion
Sudden diversification of life
