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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


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