Geology Exam # 3
Terms in this set (113)
Which of the following first appeared in the Mesozoic Era?
Fossils are more likely to be preserved under which conditions?
Which of the following first appeared in the Paleozoic Era?
Flowering plants, insects, fish, and reptiles
The radioactive isotope X, decays to the stable isotope Y. The 1/2 life of this process is 1500 million yrs. If the original amount of X has been reduced by 50%, how old is the rock that contains isotope X?
3000 million years
The radioactive isotope X, decays to the stable isotope Y. The 1/2 life of this process is 300 million yrs. If the original amount of X has been reduced by 94%, how old is the rock that contains isotope X?
1200 million years
A layer of shale lies above a layer of limestone. Each layer contains different fossils. Which are potential explanations for these contrasts?
Layers are formed in different environments containing different species, the fossils represent organisms living at different times in Earth's history
Match the following parent isotopes with their daughter isotopes-
Thorium-lead, rubidium-strontium, potassium-argon, uranium-lead
The 1/2 life of a radioactive isotope 100 million yrs. Scientists testing a rock sample discover that the ratio of parent and daughter isotopes indicates that the rock is 200 million years old. What % of parent isotopes would be present in the sample?
Which of the four organisms were the last to show up in the geologic record
Which organisms were found in the oldest rocks?
If you began with 4000 radioactive isotopes, how many parent isotopes and daughter isotopes would be left after two half lives?
1000 parent; 3000 daughter
Which radioactive isotope would be best to use to date the age of charcoal in a Native American fire pit?
Approx. what age was determined for the oldest rocks that have been found on Earth?
4 billion yrs
Ages were calculated for 4 rocks. Which of the following rocks would be classified as Precambrian
Rock D-720 million yrs, Rock B-2000 million yrs, Rock C-3800 million yrs
Radioactive decay allows scientists to determine..
When lava erupted, when granitic magma solidified below ground, when metamorphism recrystallized calcite minerals in marble
The principle of original horizontality states that
sedimentary rocks are deposited as horizontal layers
If you began with 4000 radioactive isotopes, how many parent isotopes and daughter isotopes would be left after one half lives?
2000 parent; 2000 daughter
Which of the following 1st appeared in the Paleozoic Era?
insects, reptiles, fish
Fossils are more likely to be preserved under which conditions
Which of the following appeared in the Cenozoic Era?
Global extinction events mark the boundaries between which time intervals?
Mesozoic and Cenozoic, Paleozoic and Mesozoic
If you began with 800 grams of radioactive isotopes, how much of the parent isotopes would be left after two half lives?
Identify the phrase that best fits the blank in the following sentence. Ice is to glaciers as ________ to moraines
What are the two principal gases that make up 99% of dry air?
nitrogen and oxygen
Which is the most accurate statement about sea level changes over Earth's history?
Sea level is rising and but has been higher in the geologic past
T/F: The last ice age occurred because more land area was located close to the Poles
Which factor do scientists believe is most responsible for increases in Earth's temperature over the last century?
increases in the concentration of carbon dioxide, methane and some other atmospheric gases
After two half-lives, the ratio of parent to daughter isotope is 1:
A sample igneous rock formed with 500 grams of the parent isotope, Carbon-14, which has a half-life of 5,730 yrs. The same igneous rock now contains 125 grams of Carbon-14 and 375 grams of the daughter isotope Nitrogen-14. The rock has been through ___ half lives and is _____ old.
2: 11,460 years
A student examines a series of flat-lying sedimentary rock layers in the walls of a deep cannon. What principal is the student most likely to use to determine the order in which the layers were formed?
principal of superstition
A fossil bone originally contained 800 grams of a radioactive parent isotope with a half-life of 50 million yrs. Scientists analyst the bone and discover that it now contains 50 grams of the original parent isotope. Approx. how many million yrs have passed since the organism that became the fossil was alive>
Which type of surface would have the lowest albedo value?
The tropical ocean
How would the temperature of Earth differ if carbon dioxide made up 3% of the atmosphere?
Earth would be warmer
Global temps in the past 1000 yrs have:
Experienced approx. a 1 degree C, change with the most profound changes occurring in the last century
Part of the ______ Era was dominated by fish.
What features indicate the former presence of glaciers
Landscapes that contain cirques, aeries, tarns, and U-shaped valleys, Land covered by a layer of till
When did the Mesozoic Era occur?
If a fault cuts across 3 sedimentary layers, what is the age of the fault relative to the ages of the layers?
Can be reflected by low and high level clouds, can be absorbed by low and high level clouds, can be scattered by low and high level clouds.
Radioactive decay can begin
When an element is originally formed and when elements recombine to form new minerals
Which part of the Paleozoic included evergreen trees, amphibians, and early reptiles on land?
What would the average temp on earth be like without the greenhouse effect?
Much colder than it is now
When determining the sequence of past geological events, which of the principles listed below does NOT belong?
-The youngest layer is on top, and the oldest is on the bottom
-A younger magma can bake or otherwise change older rocks that are nearby
-A GEOLOGIC FEATURE IS OLDER THAN A ROCK UNIT OR FEATURE IT CROSSES
-A younger rock or deposit can include pieces of an older rock
-A geologic feature is you're than a rock unit or feature it crosses
Which is the correct order of the four main chapters of earth history from oldest to youngest
What is the best example of the characteristics of a disconformity?
Eroded surface is covered by parallel sedimentary rock layers
Which event happened last?
Age of Fish, Age of Reptiles, and AGE OF DINOSAURS
What is the principle stating that rocks toward the bottom of a sequence of layers are older than those near the top?
When was the "age of mammals?"
T/F: More solar radiation is absorbed by Earth's surface than is scattered and reflected by the atmosphere
What is the parent to daughter ratio of radioactive isotopes after four half lives?
What was the Cambrian explosion?
A period of rapid evolutionary change of many new shelled organisms.
Three Eons and Eras of geologic time and when they began and ended.
Phanerozoic= Cenozoic-66 m/yr-Present
(542 million yrs) Mesozoic-251 m/yr
Precambrian (4600-542 m/yr)
Proterozoic (2500 million years)
Archean (4600 million years)
Explain how patterns of temperature, precipitation, and cloud cover vary on earth
-Temp decreases with increasing latitude N & S of equator (equator receives 2x more solar energy than poles)
-Temp range is greater form continents than for oceans (currents mix H2O to regulate temp & because H2O has higher heat capacity than land)
-Clouds are concentrated in irregular bands parallel to equator and latitudes 60 degrees N&S. (These cloud bands feature rising air, high precipitation (rain forests), and low atmospheric pressure)
-Clear skies are concentrated in irregular band @ poles and latitudes 30 degrees N &S (bands feature dry climates, descending air, cold/hot deserts on continents)
Any systematic change in the long term statistics of climate elements such as temp, pressure, or winds sustained over several decades or longer
4 Factors that influence changes in global temps
*Climate Forcing: Change in Earth's balance
-Positive (results in incoming energy)=warmer
-Negative (results in outgoing energy)= cooler Earth
*Natural external forcing: gradual changes in solar emission or changes in Earth's orbit
*Natural internal processes of the climate system (more/less ice cover, volcanic eruptions)
*Anthropogenic (caused by humans) forcing: more green house gases and air pollution
Examples of Positive Forcing
Changes in solar output (either), Variations in Earth's orbit (either), Changes in land use patterns (crops replace forest)-(either), Higher sea levels/melting of sea ice decrease albedo, Release of greenhouse gases by burning fossil fuels
Examples of Negative Forcing
Changes in solar output (either), Variations in Earth's orbit (either), Changes in land use patterns (crops replace forest)-(either), Air pollution can reflect solar radiation, Volcanic ash, dust, reflect solar radiation back into space, increase in reflectivity (albedo) from more high clouds
Why is Earth warm enough to support life?
Infrared radiation from Earth's surface is absorbed by gases in the lower atmosphere
-measure of the reflectivity of a surface
Light surfaces: high albedo= more reflection
Dark surfaces: low albedo= less reflection
Why is it colder in winter and warmer in summer?
Seasonal temps contrasts are due to the tilt of Earth's axis and angle of Sun's rays (Tilt= 23.5 degrees)
What must happen to the tilt angle of Earth's axis in order to have vertical rays of sunlight strike the surface where you live on the summer solstice (June 21)?
Tilt would increase
Shape of orbit changes distance to sun (100,000 yr cycle)= circular/eliptical
Tilt of axis
changes determine where solar radiation received (41,000 yr cycle)= 22-25 degree change
direction of tilt of axis changes (23,000 yr cycle)
Ice age separated into cold and warm intervals:
-cold glacials: 100,000 yrs long, 5-10 degrees celcius colder than today
-warm interglacials: 10-20,000 years long= modern temps
long lasting mass of ice that moves downslope under its own weight
Alpine (mountain) glaciers
-move 5-50 meters per year, move slowly, bare slopes, present in high US mountains like Alaska, Colorado, Washington
in cold environments (Greenland, Antarctica), can move hundreds of meters per year, Large, cover thousands of square miles, centered on land-continental crust, but some at sea
Glaciers and Glacial Environments
High Elevations, cause erosion and deposition, create characteristic landforms and deposits
-U-shaped valleys (erosion), striations on bedrock (erosion)(indicate movement of glacier), Erosion (sharp narrow ridges), glacial erratic (deposition)
Glacial deposits are mostly dumped when ice melts and so are often unsorted with a mix of grain sizes
shaped mound features formed from unsorted glacial till
Ridges that mark where the glacier paused (depositional)
Features with sorted sediment indicate an origin involving running water such as streams under the glacier
streams formed as the glacier melted
features formed from left over ice blocks that melted (deposition)
Climate & Ice
Arctic sea ice coverage:
-Seasonal changes-more in winter, less in summer (ice)
-Recent trends: 20% less ice in recent yrs and spring melt begins 2 weeks earlier
Long term climate cycles
Millions of year due to locations of continents and oceanic circulation (plate tectonics)-ex: whole ice ages
-The gap between NA & SA closed and triggered an ice age that lasted 2 million years
If water becomes trapped
Sea level changes
Bigger glaciers vs. smaller
fall into sea level; rise in sea level
B-Slower seafloor spreading, colder ocean floor=drop in sea level
S-Faster spreading, warmer, elevated ocean floor=rise in sea level
B-ocean cools, water contracts=drop in sea level
S-warming oceans=rise in sea level
Why does sea level rise and fall?
Changing climate conditions
Can be reflected, scattered, or absorbed
Solar Radiation Info
51% of solar energy will be absorbed by Earth's surface, 30% of incoming solar energy will be reflected and scattered by atmosphere, clouds, and Earth's surface
19% of sunlight is absorbed by clouds and atmosphere
Solar Radiation cont.
-Earth's surface warms as it absorbs solar energy that is not reflected or absorbed by atmosphere
-Warm surfaces emit heat energy as infrared radiation
-Infrared radiation is absorbed by greenhouse gases in the lower atmosphere (greenhouse effect)
-Solar radiation energy balance if Earth emits and absorbs the same amount of solar radiation
-But, Earth is currently absorbing more solar radiation than it is emitting back to space
How do some scientists figure out temps in the geologic past?
Recent weather records, historical records, growth rings of trees and corals, ice layers, pollen, oxygen isotopes (1,000,000+years)
Avg. global temps have increased over the last century
Viking settlement of North Atlantic islands from 900 AD
Medieval Warm Period
warmer period of earth history: 900-1400
Little Ice Age
Colder 1400-1800; Viking died out on Greenland``
Short Term Proxy records
tree rings (double of light and dark wood each year and ring width increases with wetter climates), coral growth rings, ice layers, lake sediments
Younger Dryas interval (12,000 yrs ago)
Pollen trapped in ice was climate proxy
Long-Term proxy records
Two oxygen isotopes present in oceans
-16O, lighter-evaporates more easily
-18O, heavier-remains in oceans
Scientists collect sediment cores, they split core, microfossils in core can be analyzed (18O/16O ratios in shells record changes to seawater chemistry that relate to global temp changes
Non glacial period (now)
16O leaves ocean by evaporation but returns by streamflow
18O/16O ratio stays the same
18O leaves ocean by evaporation and is trapped in glaciers
18O/16O ratio in ocean increases (less16O)
Long term proxy climate records
-Comparing ratios of isotopes to modern environments allows reconstruction of climate
-Colder climates-16O is trapped in ice, increased proportion of 18O in ocean, fossils
Long term proxy climate records 2
-warmer climates-16O released as ice melts, increased proportion of 16O in ocean, fossils
What are the 2 most common gases in Earth's atmosphere?
oxygen and nitrogen
Predict the avg. annual temp at Earth's surface
15 degrees C; 59 degrees F
Why is there life on Earth but not on other planets?
Liquid water, gravity and protective atmosphere, life-sustaining gases, A strong magnetic field
Composition of Earth's atmosphere just right to absorb enough heat to keep average temp at 59 degrees F and 15 degrees C.
-Green house effect due to: greenhouse gasses-water vapor, carbon dioxide, and methane that absorb heat in lower atmosphere. Without greenhouse effect, avg. global temp would be 18 degrees C and 0 degrees F
-An erosion surface representing a gap in time between the formation of two sections of rock
-Gap in time may be 1000s or billion yrs
-Look for contrasts in orientations, type of rocks between adjacent rock units
*3 types: angular unconformity, nonconformity, disconformity
Non-layered rock (igneous, metamorphic)
-Forms deep below surface, later uplifted to shallow depths
-Weathering and erosion expose rocks
Sedimentary rocks later deposited on erosion surface (nonconformity surface)
initial sedimentary deposits will contain pebbles (clasts) of underlying rock
-Relative Time-the sequence of events, places rock units and geologic events in order, oldest to youngest
-Numerical Time-How geologists figure out the ages of rocks, and hence the age of the Earth
Occurs when an isotope loses or gains protons and/or neutrons (results in changes in atomic number and/or mass number
A plutonic igneous rock would be _____ than the rocks that surround it
A fault would be _____ than the rocks around it
Age of Rock =
# of half-lives of radioactive isotope x length of one half life
Correlation matches attributes such as
Rock type, position and sequence, numeric ages of associated igneous rocks, and fossils
How did water get on Earth?
Commet Thea and outgassing (volcanic)
Where did earth's moon come from?
Formed from early collision of planetary bodies
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