chapter 8 learn smart
1406 million years
235u has a half-life of 703 million years. if a geologist starts with a sample that is 1 mg today, how long would it take for there to be 0.25 mg remaining?
formations
What do you call bodies of rock of considerable thickness with recognizable characteristics that make them each distinguishable from adjacent rock units?
angular unconformity
a _____________ ______________ is a contact in which younger strata overlie an erosion surface on tilted or folded rock layers
disconformity
a contact between beds that are parallel to one another; however, there are missing rock strata between the beds
an atomic number that is one more than, the same atomic mass number as.
a daughter isotope formed by beta decay will have ___________ the parent isotope
it often looks like just another sedimentary contact
a disconformity is the hardest unconformity for geologists out in the field to detect because ___________
key
a distinctive layer, known as a _________ bed, can be used to correlate rocks over great distances
the rock was tilted after sedimentation and lithification
a layer of sedimentary rock that is tilted to a high degree suggests that...
numerical time brackets are provided but not an actual age.
a limitation that occurs when dating a sedimentary rock layer by using radiometric ages of laconic ask layers above and below it is that...
stratigraphy
a subdiscipline of geology that studies interrelationships between layered rock or sediments to interpret the geologic history of an area
3.5 billion years
according to currently available geologic evidence, life appeared on the earth about ____________ ago
four
all of geologic time is divided into ______ eons
nonconformity
an erosional surface separating deep crustal rocks from much younger sedimentary or volcanic rocks
short-lived, widespread
an index fossil is both _____________-lived and occurs over a ______________ geographic area
birkland formation
applying the principles of original horizontality, which of these layers were deposited before a major tectonic event?
has a relatively short half-life
carbon-14 is useful in dating archaeological and very recent geologic events because it...
an unusual sequence of rocks is used
correlation by similarity of rock types is more reliable if...
isotopic dating
determining the age of a rock through its radioactive elements is called...
e
during which time period did rock layer x form?
it indicates the sediments must have been deposited at the same time when all the species were present
finding several species of fossils, rather than just one, in the same rock layer is more useful for correlation with other rock layers because ______________
any period of earth history can by identified by fossil species, fossil species evolve and go extinct over time, they are common in sedimentary rocks.
fossils are very useful for correlation of rock units because...
25,000
if a sample of isotope z had 100,000 atoms and had a half-life of 5 years, how many atoms of the isotope would remain after 10 years?
cross-cutting relationships, lateral continuity?, original horizontality
if you were to order the different rock layers in the image below from oldest to youngest, you would apply the principle of ____________ for the dike and granite; the principle of ____________ for the rocks near the canyon; and the principle of ____________ for the Leet Junction Formation.
the lava cools and solidifies rapidly, giving an accurate formation age
igneous rock from lava flows provides the best isotopic dates because...
contact metamorphism, cross-cutting relationships, presence of inclusions, principle of superposition, pebbles of granite
in this figure, what evidence can be used to determine that the granite is younger than the tilted layers and older than the horizontal layers?
they are physically continuous with each other
it is possible to state with confidence that the rocks at locations a and b in this photo are part of the same unit, because...
radioactive decay
lord kelvin's estimate of the age of the earth was based on his calculation of the rate at which the Earth is losing heat. his estimate, however was too young because he did not know that ___________ ____________ produces heat within the Earth.
jurassic - mesozoic paleogene - cenozoic silurian - paleozoic
match the geologic period with the ear in which it occurred
paleozoic - ancient life mesozoic - middle life cenozoic - new life
match the name of each geologic era with its correct meaning
4.5 to 4.6 billion years ago, approximately 541 million years ago, approximately 252 million years ago, about 66 million years ago
match the numerical age with each of these geologic events: formation of the earth, beginning of the paleozoic era, beginning of the mesozoic era, end of the mesozoic era
precambrian - prokaryotes, algae, and soft-bodied creatures paleozoic - trilobites mesozoic - dinosaurs cenozoic - mammals
match the species with the geologic time internal they are known for
erosion
most unconformities represent periods of...
continuity
one way geologists correlate rock units is by looking for physical ___________, where the course of a rock unit can be traced physically for great distances
correlate
physical continuity, fossil assemblages, and rock type are all methods used to _____________ rock units
1) stream erosion and formation of valley 2) deposition of foster city, hamlinvillle, and skinner gulch formations 3) deposition of larsonton formation and dike intrusion 4) erosion of leet junction formation 5) intrusion of granite and tilting 6) deposition of lutgrad, birkland, tarburg, and leet junction formation
place in correct order (from oldest to youngest) the sequence of geologic events that created these formations. put the oldest event on the bottom
1) deposition and lithification of sedimentary rock 2) uplift accompanied by folding or tilting of the layers 3) erosion 4) renewed deposition on top of erosion surface
place the following events in the correct order as they relate to the formation of an angular unconformity
quaternary neogene paleogene cretaceous jurassic triassic permian pennsylvanian mississippian devonian silurian ordovician cambrian
put the geologic periods in the correct order, with the oldest on the bottom and the youngest on the top.
1) eon 2) era 3) period 4) epoch
rank the different divisions of geologic time based upon the length of time covered, with the longest at the top
1) quaternary 2) neogene 3) paleogene 4) cretaceous 5) jurassic 6) triassic
rank the geologic periods of the Mesozoic and Cenozoic, with the most recent on top
they existed for a long period of geologic time
some fossil species are of little value to geologists for correlation because...
cosmogenic
surface exposure, or _____________ dating, uses neutron radiation from space to date rock surfaces
precambrian
the __________ is the large amount of geologic time that occurred before the paleozoic
closure
the ________________ temperature is different for each isotopic pair, it is the temperature at which the isotopic "clock" starts
absolute
the age of a rock that is measured in units of time and is determined by radioactivity is referred to as the ____________ age in comparison to its relative age
cenozoic
the ancestry of the hominids back to the beginning of the ___________ era, the age of mammals
igneous
the best rocks to use for isotopic dating using closure temperatures are...
two great mass extinctions
the boundaries between the three eras of the standard geologic time scale are defined by...
dinosaurs
the creatures that evolved during the mesozoic and became the dominant land animals after the greatest mass extinction ever were the...
iridium
the element ___________ is abundant in meteors and comets but rare in the earth's crust. its presence in rocks at the k-t boundary provides evidence that a meteor impact was responsible for the extinction of dinosaurs
an asteroid impact on earth
the event that may have caused the extinction of dinosaurs was...
the time it takes for half the parent isotopes to decay
the half-life of an isotope is equal to...
determining the amount of a cosmogenic isotope in a mineral at the rock's surface, knowing the rate of increase of a cosmogenic isotope
the length of time a rock surface has been exposed can be calculated by...
radiometric dating
the numerical age of a rock is the actual number of years or some other unit of time determined by using...
over 4 billion
the oldest known rock found on earth is dated at _____________ years old
precambrian
the oldest rocks and minerals on earth's surface have been found in canada and australia and are ___________ in age
erosion to significant depths, a considerable gap in the rock record, a great amount of uplift
the presence of a nonconformity indicates __________
inclusion
the principle of _____________ states that fragments incorporated in a host rock are older than the host rock
older
the principle of cross-cutting relationships states that a disrupted pattern is __________ than the cause of the disruption.
sedimentary layers extend laterally until they taper out
the principle of lateral continuity states that...
oldest
the principle of superposition states that within a sequence of undisturbed sedimentary or volcanic rocks, the ___________ layer is at the bottom
past
the principle of uniformitarianism is stated simply as " the present is the key to the ___________"
comparison with relative age relationships, multiple test results within statistical expectations
the reliability of isotopic dating is supported by which of the following?
radioactive decay
the spontaneous nuclear change of isotopes with unstable nuclei is called __________ _________ and can be measured with a geiger counter
paleontology
the study of fossils
proterozoic, hadean, archean
the three eras of the precambrian are...
disconformities, angular, nonconformities
the three types of unconformities are...
phanerozoic
the youngest eon is the ___________, which means visible life
neogene, paleogene, cretaceous, jurassic, triassic, permian, pennsylvanian, mississipian, devonian, silurian, ordovician, cambrain
this figure shows the geologic timescale. drag the label for each period to its correct position on the geologic timescale (top to bottom)
original horizontality
this principle of __________ ___________ states that beds of sediment deposited in water form as horizontal or nearly horizontal layers
long, short
to determine the age of very old rocks, geologists use isotopes with __________ half-lives. for very young rocks, geologists use isotopes with ___________ half-lives
1) foster city formation 2) dike 3) larsonton formation 4) granite 5) tarburg formation
using the principle of cross-cutting relationships, rand theses rock units from the oldest (bottom) to youngest (top)
foster city fm
using the principle of superposition, determine which layer was formed before the hamilnville formation and after the larsonton formation?
holocene, quaternary, cenozoic
we live in the ___________ epoch, the ____________ period, and the ____________ era
4.5 to 4.6 billion
we now regard the earth as being _________ years old
electron capture, beta emission, alpha emission
what are the ways the nuclei of radioactive isotopes can change?
atomic mass number decreases by 4, atomic number decreases by 2
what happens to a radioactive isotope that undergoes alpha decay?
contact
what is the general term for any surface that separates two different rock types or rocks of different ages? this can be an erosional surface, a depositional surface, or a structural surface
amount of probable daughter isotopes is known, there must be sufficient parent and daughter atoms to be measured, rock sample shows no sign of weathering, rock sample shows no sign of hydrothermal alteration
when geochronologists examine rocks for isotopic dating, they must be assured that which conditions have been met so accuracy is reliable?
james hutton
which geologist is commonly referred to as the father of geology?
U-Pb
which isotope pair, because of its high closure temperature, is believed to give the best crystallization age of rocks?
they have different numbers of neutrons, they have the same number of protons, they have different atomic masses
which of the following are true statements about the isotopes of a given element?
cross sections, geologic maps, geological contacts
which of the following are used to determine the relative age or rock units?
rock type
which of the following can be used to correlate rock units between tow areas?
absence of a particular fossil assemblage, presence of a weathering surface at the top of a layer
which of the following indicate the presence of a disconformity?
it is based heavily upon fossil data, it was first created using relative relationships, it is a standard scale that is used worldwide.
which of the following statements are true regarding the geologic time scale?
superposition, original horizontality, cross-cutting relationships, lateral continuity
which of these are important principles of stratigraphy?
difficulty in dating sedimentary rocks, finding datable rock at the right place in a stratigraphic sequence, finding the right kind of rock to date
which of these are limitations of isotopic dating techniques?
finding datable rock at the right place in a stratigraphic sequence, finding the right kind of rock to date, difficulty in dating sedimentary rocks
which of these are limitations of isotopic dating techniques?
lutgrad formation
which of these rock units is the oldest?
uniformitarianism and actualism
which two principles in geology state that the same processes and natural laws that operate in the present also operated in the past
electron capture
which type of radioactive decay involves the incorporation of an electron into a proton, forming a neutron?
angular unconformity
which type of unconformity is shown here? (red rock)
because carbon has a short half-life
why is radiocarbon dating only useful when dating items and events younger than about 40,000 years
