Unit 5 Poss. Test Questions Flashcards
How do we use the name Precambrian?
Precambrian is an informal name for the earliest chapter in Earth’s history.
Which range of Earth’s history is represented by the Precambrian, in BY (billions of years)?
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Which two rock types represents most of the Precambrian outcrop surfaces?
Igneous and Metamorphic rocks.
What type of fossil is most representative of the Precambrian?
Very few fossils are found in the Precambrian; most are single-cell organisms.
Where is found the largest North American Precambrian exposure?
The largest North American exposure is found around the Hudson Bay, Canada.
Where can we find exposures of Precambrian rocks in Texas?
- Llano area
- Central TX
- Carrizo Mt. near Van Horn, TX
- Franklin Mts. at El Paso, TX
How do we use the term “basement rocks”?
Usual name for Precambrian rocks.
Define a (Precambrian) shield.
Exposed portion of the basement of a continent that is composed of Precambrian rocks.
Define a platform.
“Buried” or covered surfaces of a shield.
Define a craton.
A craton is the nucleus of a continent made up of a shield and a platform.
What is the Canadian Shield?
The exposed portion of the North American craton.
What are the only representative “rocks” for the very beginning of the Hadean Eon?
4.28 BY old rocks in Nuvvuagittuq greenstone in Ungava, Quebec, Canada.
What is Earth’s oldest “particle” known and its age in BY?
Dated at 4.404 BY, one zircon crystal represents the oldest particle on planet Earth.
What time period (BY) is represent by the Archean Eon?
Represents period of 4.0 BY - 2.5 BY.
Which country do we find Earth’s oldest crustal rocks?
The Acasta gneiss is Northern Canada.
Describe the effect of the moon on Earth’s surface and oceans during the Early Archean Eon.
- Earth’s crust rose and fell 200 feet every day.
- The oceans were subjected to 1,000 foot tides.
When did a large number of meteorites stop pelting the Earth?
Meteorites continued to pelt the Earth until 3.8 BY.
What type of tectonic feature can create continental crust?
Convergent of oceanic crusts. Creates islands arcs.
Describe the rocks surrounding a typical Precambrian geologic province.
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What is graywacke sandstone and what type of environment would it represent?
A sandstone called graywacke that shows a decrease in grain size from the bottom to the top of the bed and composed of abundant clay and volcanic rock fragments. Graywackes always form in deep waters either beyond a continental shelf or off an oceanic island.
What is a “greenstone”?
A greenstone is former volcanic and sedimentary rocks that are rich in chlorite.
What do greenstone belts represent?
Greenstone Belts are zones of rocks rich in chlorite.
Where do we find United States’ oldest crustal rocks and what is the formation name?
In the Minnesota River Valley is the Morton Gneiss which is dated at 3.5 BY, thus holds the record as the oldest US rock.
At what period of time was Earth’s first ice age (BY)?
At the beginning of the Early Proterozoic, Earth experienced its first ice age of continental glaciation (2.7 - 2.5 BY).
What is a tillite? Sometimes it is also called a _____.
A tillite is a sedimentary deposit that includes rocks and boulders from icebergs. Sometimes it is also called a dropstone.
How do we subdivide the Proterozoic Eon (using modifiers)?
Early, Middle, and Late.
What are banded iron formations?
Banded Iron Formations (BIF) are alternating layers of iron oxides and chert deposited in the sea (chert is a type of quartz).
Why do we no longer fin BIF after 2.0 BY?
After 2.0 BY there would be so much free oxygen (about 1%) that very minor dissolved iron would reach the ocean and there would be no more thick deposits of BIF.
What tectonic event occurred near Missouri during the Middle Proterozoic Eon?
North America began ripping apart, withe the Mid-Continental Rift.
What mineral resources do the Keweenawan basalts contain?
The Keweenawan basalts are famous because they contain enormous amounts of copper metal and silver metal.
Which supercontinent was created with the Grenville Province?
The Grenville was formed by continental collisions during the formation of the supercontinent Rodinia, the first supercontinent (1.3 - 1.0 BY).
How long was a typical day during the middle Proterozoic?
8 hour day.
What famous Texas feature was created with the Grenville Province?
The central Texas (Llano area) “Enchanted Rock” granite mass was part of the 1.2 BY Grenville province.
What is the snowball Earth theory?
The snowball theory is a time when the entire Earth was covered with ice.
Which supercontinent was created during the Late Proterozoic Eon?
During this time the land masses recombined to form the supercontinent Pannotia (650 MY).
All living matter is composed of at least four elements; What are the elements?
{CHON} All living matter is composed of chemical compounds of the elements Carbon, Hydrogen, Oxygen, and Nitrogen. {CHON}
What is S.E.T.I?
Search for Extra-Terrestrial Intelligence.
What would be a primordial soup?
A primordial soup is organic compounds, formed by a variety of processes, from molecules that accumulate in the shallow oceans.
What is a microsphere?
Microspheres are simple organic molecules that show great organizational complexity.
- Some contain more than 200 linked amino acids.
- Some have been found forming near hot springs of volcanic vents.
- Some can grow and divide but are not considered living.
- Some scientist feel that the original life on Earth passed through a microsphere phase.
How often has man been able to create life from chemicals?
Zero.
What was Miller able to create?
Miller (1953) was able to create all 20 amino acids, using only methane, ammonia, water, hydrogen gas and a spark of electricity in a glass apparatus.
What is meant by chemical fossils?
A chemical fossil is fossil life detected by using non-radioactive isotopes of C12/C13 from “carbon films”.
What is the difference between an autotroph and a heterotroph?
Autotrophs create their own food. Heterotrophs eat autotrophs for food.
What is cyanobacteria?
Cyanobacteria are aquatic bacteria that uses photosynthesis.
In what type of rock are most very early Precambrian fossils found?
Most are found in black chert.
What is the approximate age (BY) of some of the oldest body fossils found?
Some of the next-oldest body fossils discovered are filaments of cyanobacteria aged at 3,465 BY, found withing the Warrawoona Group in Australia.
What are stromatolites?
Stromatolites are cyanobacteria and other bactera that form colonial associations.
-Mound-like structures consisting of laminated carbonate rock produced by trapping of sediments by groups of organisms (cyanobacteria).
What are Eukaryotes?
Eukaryotes are important in that they have more advanced cells than bacteria. {Eukaryotes have a nucleus}
What are acritarchs?
Acritarchs are cysts of algae. In time of drought algae will create a cellular wall called a cyst to protect itself.
Based on the fossil record, what represents the oldest known multicellular organism?
2.1 BY multicellular algae in Michigan with the Negaunee Iron Formation.
What are metazoans?
Individual cells would clump together and form multicellular animals (metazoans). {and plants (metaphytes}
What type of fossil evidence do we have for very old metazoans?
Animal Burrows, aged at 1.2 BY have been found in Australia and West Texas (during Rodinia).
What are Ediacaran fossils?
Ediacaran fossils were soft-bodied creatures with no jaws and there were no predators.
Describe the climatic environment where Ediacaran organisms lived.
The Ediacaran fauna existed in shallow, cold water marine environments, between 750 MY - 520 MY.
