Deck 23: Geologic Timereading the Rock Record

Question 1

An unconformity can be interpreted as

A)an occurrence of radioactive decay.
B)repeated intrusions of igneous rock.
C)a buried surface of erosion.
D)the result of repeated volcanic action.

Answer 1

C

Question 2

In a sequence of rock layers we find trilobite fossils at the bottom of rock layer 1 and dinosaur fossils directly above the fossil trilobites in layer 2. There are inclusions of trilobites in layer 2. We conclude that

A)dinosaurs were extinct long before trilobites came into existence.
B)dinosaurs are from the Cambrian Period.
C)by inclusion and faunal succession, layer 1 is older than layer 2.
D)there is no time gap between the rocks.

Answer 2

C

Question 3

An assumption that Earth processes occurring today have always occurred is called

A)the principle of superposition.
B)uniformitarianism.
C)the principle of original horizontality.
D)theory of unconformity.

Answer 3

B

Question 4

The principle of original horizontality states that each

A)sedimentary layer is older than the layer above.
B)sedimentary layer is younger than the layer above.
C)new layer of sediment is laid down nearly horizontally over older sediment.
D)new layer of sediment is laid down accordingly.

Question 5

An unconformity is

A)a scientific debate between Earth scientists.
B)when younger igneous plutonic rock s are above older sediments.
C)a continuous sequence of sedimentary layers.
D)a gap in an otherwise continuous time-sequence of rock layers.

Question 6

Fossils are found in

A)sedimentary rocks.
B)metamorphic rock.
C)igneous rocks.
D)sedimentary and some metamorphic rocks.

Question 7

In any sequence of sedimentary rock layers that have not been subjected to stress, you would expect to find

A)horizontal layers.
B)older layers at the bottom and younger layers at the top.
C)fossils in the bottom layers and inclusions in the upper layers.
D)older horizontal layers at the bottom with younger horizontal layers at the top.

Question 8

An eroded surface of metamorphic rocks on which a horizontal bed rests is called a

A)strata.
B)dike.
C)nonuniform surface.
D)nonconformity.

Question 9

In a sequence of rock layers we find trilobite and dinosaur fossils. The dinosaur fossils are at the bottom of the rock sequence and the trilobites are at the top. This sequence tells us that

A)dinosaurs are older than trilobites.
B)the beds are overturned.
C)trilobites survived the age of the dinosaurs.
D)the beds are folded.

Question 10

The theory that different forms of animals throughout Earth's past occurred in a definite order is called the principle of

A)fossil assemblage.
B)faunal succession.
C)conformable fossils.
D)fossil determination.

Question 11

In a thick bed of sedimentary rocks we find an igneous dike. The order of formation is

A)together.
B)igneous before sedimentary.
C)sedimentary before igneous.
D)unknown.

Question 12

Which relative dating principle states that in an undeformed sequence of sedimentary rocks, each layer is older than the one above and younger than the one below?

A)Original horizontality.
B)Superposition.
C)Cross-cutting.
D)Inclusion.

Question 13

The principle of faunal succession states that

A)fossil organisms follow one another in a definite, irreversible time sequence.
B)rock cycling may dislodge and relocate fossils, making their age difficult to determine.
C)fossils are always older than the rock in which they are found.
D)fossils are ordained.

Question 14

Conditions for the preservation of fossils are best achieved

A)in desert environments.
B)in glaciated environments.
C)in shallow river beds.
D)on the floors of shallow seas.

Question 15

When comparing geologic time to a calendar year, the time of the dinosaurs is in the

A)middle of October.
B)first half of December.
C)second half of December.
D)first half of February.

Question 16

In a sequence of rock layers we find trilobite fossils at the bottom of the rock sequence and dinosaur fossils directly above the trilobite fossils. We conclude that

A)trilobites survived up to the time of the dinosaurs.
B)the beds are overturned.
C)the processes of erosion created a gap between the age of trilobites and the age of dinosaurs.
D)dinosaurs fed on trilobites.

Question 17

Deposition of sediment with each new layer younger than the layer below illustrates the principle of

A)original horizontality.
B)superposition.
C)nonconformity.
D)horizontality and nonconformity.

Question 18

A surface of erosion between rocks that represents a gap in Earth history is

A)called a dike.
B)an unconformity.
C)a faunal conformity.
D)none of the above

Question 19

Sediments deposited in an even, horizontal manner illustrate the principle of

A)superposition.
B)original horizontality.
C)succession.
D)conformity.

Question 20

The principle of superposition states that the top layer of rock is

A)igneous.
B)the youngest.
C)sedimentary.
D)the oldest.

Question 21

On what four assumptions is the principle of faunal succession based?

Question 22

The time required for one-half of a radioactive material to decay is called the

A)absolute age.
B)half-life.
C)date age.
D)true-life.

Question 23

Fossils can be used to determine the relative age of rock layers because they are

A)found in a definite order.
B)deposited horizontally, one fossil at time.
C)radioactive.
D)found in sedimentary rocks.

Question 24

In a sequence of sedimentary rocks, the bottom layer is the youngest and the top layer is the oldest. This type of sequence suggests that the

A)principles of original horizontality and superposition are flawed.
B)beds must have been overturned by some structural disturbance.
C)dates for these rocks must be in error.
D)principles of original horizontality and superposition hold true.

Question 25

According to most estimates, Earth is approximately

A)4.5 thousand years old.
B)4.5 million years old.
C)4.5 billion years old.
D)45 billion years old.

Question 26

The laws of physics, chemistry, and geology have operated unchanged through time to shape Earth as we know it today can be summed up by the idea of

A)evolution.
B)everlasting change.
C)uniformitarianism.
D)natural history.

Question 27

The idea of uniformitarianism suggests that

A)the natural laws that operate today are different than those that have operated in the past.
B)sediments are laid down layer upon layer with younger layers always on the top.
C)the processes and natural laws that operate today have been valid throughout geologic time.
D)all rocks layers are originally uniform.

Question 28

What type of igneous formation would agree with the principle of superposition?

Question 29

What types of rocks are representative of the principle of original horizontality? Why?

Question 30

Radiometric dating is based on

A)decay of uranium-238 to lead-206.
B)sequence of rocks and the relative position of one layer to another.
C)proportions of radioactive isotopes and their decay products.
D)the half-life of radioactive atoms.

Question 31

Relative dating tells us the

A)time gaps that occur during deposition.
B)age of rock layers.
C)sequence of rock layers-which formed first, second, and last.
D)actual date of formation for a rock layer.

Question 32

What does the principle of superposition say about the ages of rocks?

Question 33

The five principles used to determine the relative ages of rock include original

A)horizontality, superposition, cross cutting, inclusion, and faunal succession.
B)horizontality, nonconformity, cross cutting, inclusion, and faunal succession.
C)inclusion, superposition, uniformitarianism, horizontality, and fossil succession.
D)horizontality, uniformitariansism, cross cutting, stromatolite, and faunal succession.

Question 34

When tilted or folded sedimentary layers are covered by younger, horizontal rock layers it is called

A)an intrusion.
B)an angular unconformity.
C)a syncline.
D)conformable.

Question 35

To help determine the age of rock layers over a large area we can use the principle of

A)original horizontality.
B)lateral continuity.
C)superposition.
D)fossil assemblage.

Question 36

How do geologists determine the relative ages of different rocks?

Question 37

To date relatively young rocks and materials, we use the decay of

A)uranium-238 to lead-206.
B)potassium-40 to argon-40.
C)carbon-14 to nitrogen-14.
D)uranium-235 to lead-207.

Question 38

To date the age of Earth, we look for rocks with a high percentage of

A)uranium-235 to lead-207.
B)uranium-238 to lead-206.
C)potassium-40 to argon-40.

Question 39

In a sedimentary rock that contains inclusions of metamorphic rock, the inclusions must be

A)older than the sedimentary rock.
B)younger than the sedimentary rock.
C)on top of the sedimentary rock.
D)below the sedimentary rock.

Question 40

The rather simple idea that, unless disturbed, younger sedimentary layers overlie older layers, is referred to as the principle of

A)original horizontality.
B)uniformitarianism.
C)faunal succession.
D)superposition.

Question 41

Granitic pebbles with a radiometric age of 300 million years are embedded in a sedimentary rock. A dike, dated at 200 million years, intrudes into the sedimentary rock. With all this information we can estimate the age of the sedimentary rock to be

A)older than 300 million years.
B)younger than 200 million years.
C)between 200 and 300 million years old.
D)precisely 300 million years old.

Question 42

Radiometric dating assumes that, once a mineral has crystallized, any daughter product results only from the decay of the original unstable parent. Some complications are

A)variations in temperature.
B)failure to take samples too close together.
C)"time clock resetting" due to metamorphism, and product leakage that yields false age estimation.
D)a poorly maintained teleometer.

Question 43

Which isotopes are most appropriate for dating formations from the following ages: (a)the early Precambrian; (b)the Mesozoic; (c)the late Pleistocene?

Question 44

If a radioactive element has a half-life of 704 million years, and the amount of parent material remaining is one-eighth of the original amount, the specimen is about

A)2,112,000,000 years old.
B)1,408,000,000 years old.
C)2,816,000,000 years old.
D)3,520,000,000 years old.

Question 45

The isotope most useful for dating rocks from the late Pleistocene is

A)uranium-238.
B)uranium-235.
C)potassium-40.
D)carbon-14.

Question 46

The oldest rocks that have been dated by radioactivity are approximately

A)2 million years old.
B)200 million years old.
C)4 billion years old.
D)10 billion years old.

Question 47

The geologic time scale is broken up into time units of different sizes based on

A)eons, eras, periods, and epochs.
B)changes in fossilization.
C)visible and nonvisible life forms.
D)major changes in life forms.

Question 48

The resetting of a mineral's time clock means that

A)a mineral can be formed and reformed again and again.
B)the date obtained will be the date of the metamorphic event, not the date of the rock's formation.
C)the date obtained will be the date of the rock's formation, not the date of the metamorphic event.
D)minerals can tell time just like a clock can tell time.

Question 49

The fundamental time unit representing a major change in life forms is the

A)eon subdivision.
B)era subdivision.
C)period subdivision.
D)epoch subdivision.

Question 50

What are some of the uncertainties in obtaining radiometric carbon dates?

Question 51

A radiometric date is determined from mica that has been removed from a rock. What does the date signify if the mica is found in granite? What does the date signify if the mica is found in schist?

Question 52

Radiocarbon dating is limited to the remains of plants and animals that died no longer than about

A)100 years ago.
B)5700 years ago.
C)40,000 years ago.
D)1,000,000 years ago.

Question 53

By radiometric dating, the oldest mineral in a sedimentary rock was found to be 1.4 million years old. What is the age of the sedimentary rock?

A)Radiometric dating does not work for sedimentary rocks.
B)1.4 million years.
C)No older than 1.4 million years.
D)No younger than 1.4 million years.

Question 54

The ultimate truth of any radiometric date depends on the

A)size of the given sample.
B)chemical composition of the sample being tested.
C)precision and accuracy of the lab techniques.
D)reset date of the sample.

Question 55

In dating a mineral, what is meant by "resetting of the mineral's time clock"?

Question 56

What are the limitations in obtaining radiometric dates?

Question 57

The numerical dates associated with events on the geologic time scale were determined by

A)relative dating.
B)superposition.
C)radiometric dating.
D)fossil assemblages through time.

Question 58

To date a rock thought to be many millions of years old, you should NOT use the decay of

A)uranium to lead.
B)potassium to argon.
C)carbon-14.

Question 59

If the half-life of some radioactive element is 1 billion years, and a mass of rock originally contained 100 g of that element, how many grams of the radioactive element would be left after three billion years had passed?

A)6.25 g
B)12.5 g
C)25 g
D)50 g
E)none

Question 60

The process where an element spontaneously changes into a different element (transmutation)by a change in the nucleus of an atom is called

A)radiometric dating.
B)radioactive decay.
C)radiometric decay.
D)none of these

Question 61

During the Precambrian, the development of the ozone layer helped

A)primitive organisms on Earth's surface to nucleate.
B)shield Earth's surface from harmful ultraviolet radiation.
C)promote the emergence of stromatolites.
D)promote the development of anaerobic organisms.

Question 62

Describe the conditions of Earth during the Precambrian.

Question 63

The oldest known fossils are

A)trilobites and brachiopods.
B)algae and bacteria.
C)fungi and algae.
D)worms and jellyfish.

Question 64

The Devonian period is most noted for the

A)ability of certain fishes to breath air.
B)ability of certain fishes to move onto land.
C)first amphibians.
D)great diversification of fishes-some developed lungs, some moved to land, and some became amphibians.

Question 65

Development of Earth's early oceans was likely due to

A)water-rich meteors bombarding Earth's surface.
B)volcanic outgassing in Precambrian time.
C)intense convection in the mantle, and severe heat dissipation from Earth's interior.
D)cooler temperatures that promoted the condensation of water vapor in the atmosphere.

Question 66

The banded iron formations began to form when

A)carbon dioxide dissolved in seawater.
B)varying oxygen levels allowed the precipitation of alternating layers of iron oxide.
C)oxide minerals were deposited on the ocean bottom.
D)iron from lava flows settled into layered formations.

Question 67

What was the one most important event in the Precambrian?

Question 68

The most important event during the Cambrian period was the

A)emergence of the fishes.
B)ability of organisms to form an outer skeleton.
C)emergence of the trilobite.
D)ability of organisms to develop lungs.

Question 69

The Precambrian witnessed the development of

A)the first atmosphere.
B)the ozone layer.
C)photosynthesis.
D)photosynthesis, an oxygenated atmosphere, and the ozone layer.

Question 70

Large deposits of gypsum and other evaporite minerals are evidence of

A)volcanic activity during the Cambrian period.
B)dried up shallow seas from the Silurian period.
C)seafloor spreading during the Permian period.
D)glaciation during the Triassic period.

Question 71

Which of the following is NOT true of the fossil record?

A)The fossil record spans 3 billion years of Earth's 4.6 billion year age.
B)The most common fossils are from organisms that had hard parts like shells and bones.
C)Similar to present day stromatolites, the first fossils were simple, anaerobic algal plants.
D)The Paleozoic era is credited with the emergence of life.

Question 72

Sea level fluctuated several times during the Paleozoic. Which of the following is NOT a representative factor for sea level rise in the Paleozoic?

A)Melting of continental glaciers.
B)Ocean basins stood high on the asthenosphere due to active seafloor spreading.
C)Ocean basins stood high on the asthenosphere due to slow but continuous seafloor convergence.
D)The breakup of the Precambrian supercontinent

Question 73

Why are periods the most fundamental time unit?

Question 74

Rocks from the Carboniferous period are significant because they

A)contain diamonds.
B)provide gold and silver deposits.
C)have large deposits of coal and oil.
D)are a source of cement.

Question 75

Life forms in the Precambrian included

A)trilobites.
B)brachiopods.
C)coelacanths.
D)cyanobacteria.

Question 76

The Paleozoic era begins with the Cambrian and concludes with the

A)Ordovician period.
B)Silurian period.
C)Permian period.
D)Triassic period.

Question 77

Earth's first atmosphere was rich in water vapor but poor in free oxygen. The atmosphere became more oxygenated with the

A)development of the ozone layer.
B)emergence of stromatolites that developed a simple version of photosynthesis.
C)emergence of gases from volcanic eruptions.
D)both A and B.

Question 78

Life forms in the Precambrian include

A)trilobites, brachiopods and stromatolites.
B)cyanobacteria and trilobites.
C)the agnatha and the coelacanths.
D)stromatolites and certain primitive blue-green algae.

Question 79

The Carboniferous period is well noted for the

A)emergence of the insect.
B)evolution of the amniotic egg.
C)age of the reptiles.
D)extinction of shallow water organisms.

Question 80

The oldest known fossils of single-celled organisms are

A)4.6 billion years old.
B)3.9 billion years old.
C)3.3-3.5 billion years old.
D)1.3-1.5 billion years old.