CHAPTER 9

Carbon-14

Charcoal incorporated into recent sediment

Middle Paleozoic

Fish became diverse and abundant in the ocean.

What sort of information can we get about the rocks on the surface from their exposure to cosmic rays?

How long they have been at the surface

Which of the following types of data could be used by geologists to estimate the age of past Earth events?

Ice cores Lake varves Tree rings

Uniformitarianism can be stated as ______.

"the present is the key to the past"

Examine the image. Which number represents the oldest rocks?

1. (far left)

Isotopic dating is accomplished by assigning ages in years to rocks using ______ dating methods.

analytical

Isotopic dating means that ages are assigned to rocks using ______ methods.

analytical

Isotopes that decay slowly are used to date ______.

ancient rocks

Which principle of relative dating can be used to determine when the minerals associated with the granite intrusion in the diagram formed?

cross-cutting relations

The vast majority of impact cratering occurred ______.

early in Earth's history

Put the groups of creatures in chronological order according to their prevalence/appearance in the Paleozoic, with the most recent on top.

1. Amphibians and early reptiles 2. Coral reefs, insects, ferns 3. Crinoids, molluscs, trilobites, snails

Facies change

Different sediments are deposited due to a change in the environment.

A jellyfish is unlikely to become a fossil because it lacks ________ parts. (Use just one word for your answer.)

solid/hard

The sedimentary rocks numbered 4 to 7 can be ordered using the principle of __________.

superpositon

This graph showing data gathered from minerals within a granite shows that ______.

various isotopic systems are necessary to get more than one date we can determine its cooling history using various isotopic systems

Zircons are used to date ______.

very old rocks

Isotopes can be used to date ______, which can be found in fractures in granite, or in the pore spaces in sediments or sedimentary rocks.

water

The isotopic evidence for the numeric dating of very old rocks in Canada and Australia relies upon crystals of the mineral ________.

zircon

Place the events that formed the landscape shown in the correct sequence, from first event at the top to last event at the bottom.

1. Sedimentary layers are deposited horizontally 2. Sedimentary layers are lithified 3. The river cuts through the rock layers 4. The canyons widen and tributaries form.

Mesozoic

Middle life

Select the correct eras that are used in the geologic timescale from the choices below.

Paleozoic Mesozoic

Inclusions

Rocks may incorporate older pieces of rock

Desert varnish

Rocks without this are used in relatively young constructions.

James Hutton inferred that the rocks below the contact at Siccar Point were vertical gray sandstone and shale and the rocks above were gently dipping red sandstone and conglomerate. Therefore, the histories of these rocks were ______.

different

Because all of the rock layers in the photograph are horizontal sedimentary rocks, this unconformity is called a(n) __________.

disconformity

The formation of impact craters on Earth was most common ______.

during the early Precambrian

Special rocks found in Antarctica are dated with isotopes to give an average age of Earth of 4.55 billion years. We can use these dark-colored ____________ because scientist assume they were formed at the same time as Earth.

meteorites

Which of the following are principles of relative dating?

Superposition Original horizontality Cross-cutting relations

The first organisms on Earth included ______.

algae

Early Earth would have been inhospitable to many life-forms of today because the ______.

atmosphere lacked oxygen

Isotopes are different forms of an element that have different ______.

atomic weights numbers of neutrons

The discovery of radioactivity in the early 1900s allowed geologists to determine the age of Earth to be approximately 4.55 _______ years.

billion

Reproductive strategies, climate, competition, and adaptability are factors that influence whether a species survives or becomes __________.

extinct

Since 99.9% of all species that have lived on Earth are extinct, it is reasonable to assume any fossil that is found is of a(n) ________species.

extinct

True or false: The unconformity is older than the isotopic age of the granite because it is found above it.

false

If a creature has hard parts and is rapidly buried after death, it is more likely to become a(n) __________.

fossil

The geologic timescale details and divides geologic time based upon ____.

fossil data

Concretions and dendrites in rocks are often mistaken for ______ but these features form inorganically.

fossils

William Smith established the principle of ___________ succession from the information he gathered while surveying rocks along canals in England, Wales, and Scotland. There he collected fossils and noted which ones were common in which layers.

fuanal

Rocks formed during the earliest parts of Earth's history include those that are shattered rock pieces surrounded by a glassy matrix, and metamorphosed ultramafic lava flows called ______.

greenstone

The oldest __________ cores in Antarctica have over 100,000 annual layers.

ice

Stratigraphy is the ______.

study of sequences of rocks, including the rock types, fossils, and inferred environments

Contact effects

A baked zone forms next to a dike during intrusion

Restricted event

A deposit is of limited aerial extent

What are ways that rock units in two different stratigraphic sections are correlated?

A distinct formation is in both sections. An unconformity can link the two sections.

U-Pb

A solidification of a granite

K-Ar

A volcanic eruption

Which factor would help ensure survival of one species over another?

Adaptability to environmental change

Different analytical dating methods can be used on the same rock. What types of information can be learned about a rock's history using these methods?

Age when magma solidified How fast an igneous rock cooled through time

Paleozoic

Ancient life

Ancient rocks must be dated with isotopes with a ______ half-life.

long

Rocks contain evidence that which of the following processes occurred throughout Earth's history?

Mountains were uplifted and eroded. The seas advanced and retreated. Different types of creatures lived and became extinct.

Which unconformity is produced when an eroded surface of an igneous or metamorphic rock is buried by layers of sandstone and conglomerate?

Nonconformity

How many species that have ever existed on Earth are now extinct?

Nearly all (over 99%)

Which of these isotopic systems would be most useful for dating a lava flow from the Mesozoic?

Potassium-Argon

Inclusions

Pieces of an older building are used in a younger building.

Early Paleozoic

Sea life such are corals, crinoids, mollusks, trilobites, and snails were abundant.

Cross-cutting relations

The fault is younger than the rocks it cuts across.

Choose the only process listed that is not part of the formation of a nonconformity.

The layered rocks are tilted and deformed.

Superposition

The oldest rock is on the bottom

Superposition

The oldest ruins are on the bottom.

True or false: Cross-cutting relations can be used to determine that the Colorado River cut through the Grand Canyon after the sedimentary rocks formed.

True

True or false: Fossils can include traces and imprints of plants and animals as well as their remains.

True

Rock units may not be lateral continuous across a landscape because ______.

a facies changes of erosion restricted events that formed them

Rocks around the world contain evidence that _________ have advanced and retreated, and ___________ have been uplifted and eroded.

seas/oceans; mountains

Who discovered the principle of faunal succession?

William Smith

Which of the following materials can be dated with carbon-14 at archeology sites?

Wood Charcoal Bones

Which of the following materials can be dated using carbon-14?

Wood Shells Water Charcoal

We categorize impact _________ as either simple or complex, depending on their size and features.

craters

When an igneous dike cuts across sedimentary strata, the principle of ____________ relations can be used to determine the relative age.

cross-cutting

Describe the formation of a nonconformity by putting the following in the correct order, with the first event on top and most recent on the bottom.

1. A nonlayered rock is formed at depth 2. The nonlayered rock is uplifted to the surface 3. The nonlayered rock is weathered and eroded 4. Conditions change, and the eroded surface is buried by sediments 5. The sediment lithify

Place the isotopic systems in order, from the system best for dating the youngest materials on the top to the system best for dating the oldest materials on the bottom.

1. Carbon-14 2. K-Ar 3. Rb-Sr

Order the four chapters in Earth history from youngest at the top to oldest at the bottom.

1. Cenozoic 2. Mesozoic 3. Paleozoic 4. Precambrian

Use the mnemonic Cuddly Old Sheep Dogs Make Perfect Pets; They Just Crowd People Nearby Quietly in order to remember the periods of the Paleozoic, Mesozoic, and Cenozoic Eras. The periods are: Cambrian, Ordovician, Silurian, __________, ___________, Pennsylvanian, Permian, __________, Jurassic, Cretaceous, Paleogene, _________, and Quaternary.

1. Devonian 2. Mississippian 3. Triassic 4. Neogene

Geologic events occurred to trap oil and gas in an anticline, as shown in the diagram. Rank the geologic events from the first (oldest) event at the top to the last (most recent) event at the bottom.

1. Layer of sedimentary rocks are deposited horizontally 2. Rocks are folded into an anticline 3. Oil and gas trapped by the fold

Apply the mnemonic Cuddly Old Sheep Dogs Make Perfect Pets; They Just Crowd People Nearby Quietly to place in order some of the periods of the Paleozoic, Mesozoic, and Cenozoic Eras. Put the oldest period at the bottom and the most recent period at the top.

1. Neogene 2. Cretaceous 3. Jurassic 4. Triassic 5. Devonian 6. Cambrian

Which of the principles of relative dating would be useful in determining the age of the orange granite?

Contact effects Superposition

Trilobites first appeared on Earth during the __________ Period, when a so-called __________ of life (rapid evolutionary change) introduced many new species in a short time frame.

Cambrian; explosion

Strong evidence for a very old Earth come from the ______ in North America, from which isotopic analysis of the rocks have yielded ages of over 3 billion years.

Canadian Shield

The first humans appeared before 300,000 years ago in the ________ Era

Cenozoic

Which of the following geologic features look like fossils but are not because they form through inorganic processes?

Concretions Dendrites

Which principle can be used to determine the relative age of an igneous intrusion called a dike?

Cross-cutting relations Reason: Principle 4 states that younger rocks or features can cut across any older rock or feature.

This angular unconformity is called The ________ Unconformity, as it represents 1.3 billion years.

Great

Change in thickness

River deposits become thinner at the edge of a valley

How did Earth's oxygen-rich atmosphere develop from a carbon dioxide-rich atmosphere?

Through photosynthesis by cyanobacteria

Earthquakes

Using cross-cutting relations to determine the age of the fault

The Cenozoic Era is called the age of _________ because of their abundance and diversity during this time.

mammals

Fossils of species that lived on Earth for a long time period are often found in ______, whereas fossils of species that lived for a shorter time are found ______.

many rock layers; in a layer or two

The oldest rocks in the Grand Canyon are ______.

metamorphic Precambrian plutonic

Greenstones are representative of ______ from very early (early Precambrian) in Earth's history.

metamorphosed ultramafic lava flows

Select all that apply The age of Earth is estimated to be 4.55 billion years. This is determined by dating ______.

meteorites, the Moon

An isotope refers to any element that has the same number of protons but a different number of ________.

neutrons

An isotope refers to any element that has the same number of protons but a different number of _________.

neutrons

The Grand Canyon exposes all three types of unconformities: the ______, _______, and the angular unconformity.

nonconformity, disconformity

Fossils that existed for a very long time, especially if they show little change, are _______ useful to geologists in assigning ages

not very

In the photograph, the dark-colored rocks are inclusions within the light-colored granite. Consequently, the dark-colored rocks are __________ than the granite.

older

River terraces are _____ than the age of the modern river channel.

older

The diagram shows a dike that can be dated with isotopes. The gray limestone is ____________ than the cross-cutting dike.

older

The diagram shows a dike that can be dated with isotopes. The gray limestone is than the cross-cutting dike.

older

The principle that tells geologists the landscape formed before the lava flow formed, as shown in the illustration, is called __________.

superposition

fossil fern

thin films of carbon on a rock surface

Preserved trackways and worm burrows in rock are examples of ________ __________.

trace fossils

Organisms with soft body parts only are rarely preserved as fossils; they may leave behind indirect evidence of their existence as _________ fossils.

trace/impression

"The present is the key to the past" is a phrase commonly used to summarize the geologic concept of ___________.

uniformitarianism

James Hutton is often regarded as the father of geology. He realized that geologic features present on Earth could be explained by present-day processes, a principle today called ___________.

uniformitarianism

Relative dating _________ to determine the order in which geologic events occurred.

uses common sense uses geologic principles

The petroglyphs could be created on this rock because it is covered in desert _____________.

varnish

Indicate the typical sequence of formation for sedimentary rock landscapes, beginning with the first event at the top and the last event at the bottom.

1. Deposition of sediments in layers 2. Lithification into sedimentary rocks 3. Erosion of rocks into a landscape

Determine the sequence of events that created the rocks shown by putting the following in order, with the oldest (and first) event on the bottom and the most recent event on the top.

1. Deposition of tan sandstone 2. Land surface eroded, forming igneous pebbles 3. Cross-cutting dike intruded 4. Green shale and gray limestone deposited horizontally

Put the current periods of the Cenozoic Era in the correct order, with the most recent on top.

1. Quaternary 2. Neogene 3. Paleogene

Late Paleozoic

Amphibians and reptiles evolved on land

What is the last step in the formation of a typical landscape?

Erosion of sedimentary layers

Which of the following statements correctly identify ways that archeologists and geologists use relative-dating principles to study early human sites?

Examination of the ages of ruins with the oldest generally being found on the bottom and covered by younger habitations Examination of bones from early humans and association with small mammal fossils found in the same layer

Evolutionary theory

Favorable genetic mutations occurring in a species are more successful in small, isolated populations than in large populations.

What do geologists use to age correlate rocks?

Index fossil assemblages Magnetic signatures Isotopic ages on lava flows

Why is burial necessary for fossil preservation?

It doesn't allow the organism's remains to decompose or be scavenged

Which of the following statements are true regarding the geologic timescale?

It is based on data from fossils. It was first created using relative dating and correlation.

Had birdlike hip structures and were herbivores

Stegosaurus and Triceratops

The dating of geologic hazards is important in understanding how often they occur. What methods are used to date the hazards here?

The isotopic dating of the lava flow. The isotopic dating of sediments disrupted by the faults. The relative dating of the eroded scarp in relation to the lava flow.

True or false: Scientists used various techniques to date the age of Earth before the discovery of radioactivity.

True

What defines the boundaries between each of the three eras in the geologic timescale?

Two great mass extinctions

Fossils change through a section of rocks because ______.

different species were alive during different periods of time

The Mesozoic Era is known as the age of the _________, after the best-known creatures of this age.

dinosaurs

The principle of faunal succession states that ______.

fossil species show a systematic change with time fossil species change upward from older layers of sedimentary rock to younger layers

Geologists use _________ to document evolution in the rock record.

fossils

Groundwater can be dated using ______.

isotopes

The Paleozoic and Mesozoic Eras both end with a(n) ___________ ____________.

mass extinction

Relative dating is concerned with the _________ in which geologic units were formed, rather than with their age. (Use just one word for your answer.)

order, sequence, OR chronology

The rocks in the Grand Canyon record a ______ portion of geologic time, as there are multiple unconformities and the oldest rocks are 1.7 billion years old.

small

Subsidiary drainages on a river are known as ______.

tributaries

______ may form as erosion by a river further downcuts and widens a canyon, making a more intricate canyon formation.

tributaries

Buried erosion surfaces that represent large intervals of time are called __________.

unconformities

The dike is _____________ than the rocks it cuts across based on the principle of ________-__________ relationships.

younger; cross-cutting

Order the events that form an angular unconformity from the first event at the top to the last event at the bottom.

1. Rocks are deposited horizontally 2. Rocks are folded 3. Uplift occurs, and folded rocks are eroded 4. Horizontal rocks are deposited over eroded tilted beds

Before radioactive decay occurs, there exist 200 parent atoms. After one half-life, there would be _______ parent atoms and ___________ daughter atoms. (Insert numbers for your answers.)

100; 100

Observed changes (evolution)

Development of stronger front fins in Paleozoic fish occurred, as compared to fish fossils found in older rock layers.

Isotopic dating of basement rocks in ______ suggests Earth has a long history because the oldest rocks, from the area of the Canadian Shield, are more than 3 billion years old.

North America

The sedimentary rocks in the Grand Canyon that record the coming and going of the sea, as well as rivers and deserts, were deposited in the ________ Era.

Paleozoic

Cenozoic

Recent life

What does this ancient sedimentary rock rich in iron indicate about the conditions in which it was deposited?

There was oxygen.

A hypothesis that explains how new organisms or new characteristics can appear suddenly in the fossil record is called ______.

punctuated equilibrium

Which of the following are important about fossils in the rock record?

They are evidence of ancient life. They document the evolution of life. They can be used to date rocks.

A dark coating, known as desert ______, can occur on desert rocks that are left undisturbed for hundreds to thousands of years. It consists of iron-oxide and manganese-oxide materials.

varnish

Dinosaurs are the best-known creatures of the ________ Era.

Mesozoic

Describe the formation of a disconformity by putting the following in the correct order, with the first event on top and the most recent event on the bottom.

1. Sedimentary rocks are formed in horizontal layers 2. The rocks are exposed at the surface 3. Weathering and erosion occurs 4. Younger sedimentary rocks are deposited in horizontal layers

Using radioactive decay to date a rock, a scientist finds that only 25% of the original isotope is remaining. How many half-lives have passed?

2

Earth's atmosphere changed dramatically with the introduction of free oxygen approximately ______ years ago. A second oxygenation event began ______ years ago and brought the atmospheric concentration to its approximate current level of 20%.

2.4 billion; 700 million

Where are the oldest rocks in the column of sedimentary rocks shown in the diagram?

At the bottom

The periods of the geologic timescale are named after regions in Europe. For example, ______________ is derived from Cambria, and __________ is derived from the Jura Mountains.

Cambrian; Jurassic

Choose the organism and the process responsible for oxygenating Earth's atmosphere.

Cyanobacteria Photosynthesis

Evidence for the cause of the dinosaurs' extinction at the end of the Mesozoic era can be found at ______.

Deccan Traps, India Chicxulub crater, Mexico

When a flat-lying sedimentary rock landscape is formed, which of the following events generally occurs before lithification of the horizontal layers?

Different sedimentary layers accumulate

The end of the Paleozoic Era, marked by the extinction of about 70% of land species, is known as the Great _________.

Dying

True or false: A disconformity occurs above tilted rock layers.

False Reason: A disconformity occurs between parallel rock layers.

Identify possible causes of the Great Dying, the mass extinction at the end of the Paleozoic.

Formation of the supercontinent Pangaea Major changes to ocean structure Outpouring of lava Large meteorite impact

What geologic features could cut across sedimentary rocks and therefore are younger than the rocks they cut across?

Fractures Dikes Veins

The introduction of free oxygen to Earth's atmosphere occurred approximately 2.4 billion years ago and is called the _________ ____________ Event, or GOE. A second such event began about 700 million years ago.

Great Oxygenation

What happens to an asteroid or comet that creates a crater when it impacts a planet or moon?

It breaks apart and it often destroyed.

Erosion

Missing rocks are marked by an unconformity.

Choose all the rock types that might exist immediately below a nonconformity.

Nonlayered metamorphic rocks Granite

Choose the process that is not included in the creation of an disconformity.

Nonlayered rocks are uplifted to the surface.

Which principle can be used by a geologist to determine that the rocks shown in the photograph have not been deformed since they were deposited?

Original horizontality

Which principle of relative dating can be used at Siccar Point in Scotland to determine that the rocks below the unconformity were tilted to vertical before erosion occurred?

Original horizontality

The chapter of geologic time that is represented by simpler life forms such as bacteria and algae is the __________.

Precambrian

The oldest rocks and minerals on Earth's surface have been found in Canada, Greenland, and Australia and are from the ______.

Precambrian

Which chapter of geologic history is the earliest and represents 90% of geologic time?

Precambrian

Which three periods currently make up the Cenozoic?

Quaternary, Paleogene, Neogene

What events occurred at the beginning of the Cambrian Period, approximately 542 million years ago?

Rapid evolutionary change Explosion in the amount of diversity of life Evolution of more organisms with hard parts

Original horizontality

Sediments and volcanic unit are usually deposited in flat-lying layers.

True or false: You can use both superposition and contact effects to determine that the light-colored volcanic rock is younger than the underlying unit.

True Reason: If the contact between the units is baked, then the overlying volcanic unit altered the underlying rocks, and the overlying rocks are younger.

Diverse group of carnivores and herbivores with hip structures similar to lizards

Tyrannosaurus rex and Apatosaurus

Which statements explain why the rocks of the Grand Canyon do not represent all of geologic time?

Unconformities record missing time. Rocks from the first 2.8 billion years of Earth history are missing.

Volcanic eruptions

Using isotopic methods, such as Ar-Ar dating

Flooding

Using the amount of soil development and carbon-14 dating on terraces

Which of the following statements about James Hutton are correct?

Worked in Scotland Realized that layers of sedimentary rock are products of sediment removal and deposition Reasoned that ancient geologic features can be explained by present geologic processes Argued that the time required for geologic processes was much greater than currently perceived

The type of unconformity shown in this diagram is a(n) ______.

angular unconformity

An unconformity is a(n) ______.

buried erosion surface that is preserved beneath later deposits

The specific isotope used by archaeologists to determine the age of bones, wood, and charcoal preserved at a site is __________.

carbon-14

Baking of rocks surrounding an igneous intrusion is called _______ effect.

contact

A single index fossil can assist a geologist with ______ the rock in which it was found with all other rock layers that contain that fossil.

correlating

In geology, determining time equivalency in rocks is called ______.

correlation

Stones on a surface can be dated with isotopes that originate from _________ rays.

cosmic

Dikes, sills, veins, and fractures are features that can be used in the principle of ______ to determine the relative age of geologic events.

cross-cutting relationships

The photosynthetic organisms that are responsible for the oxygenation of Earth's atmosphere are __________. (Use just one word for your answer.)

cyanobacteria

Rapid burial of a dead organism helps to preserve it from being destroyed through ___________.

decomposition OR scavenging

The principle of original horizontality means that flat-lying sedimentary rocks have not been ______.

deformed

The geologic timescale is subdivided into three __________ since the end of Precambrian.

eras

The fossil record has been used to document observed changes in organisms over time; in other words, it has been used to study ______.

evolution

Some fossil species are of little value to geologists for correlation because they ______.

existed for a long period of geologic time

_____ are evidence of ancient life in sedimentary rocks.

fossils

dinosaur bones

hard parts buried and preserved

fish with fins and scales

impressions on a lake bed

A fossil that is a very short-lived, geographically widespread species known to exist during a specific period of geologic time is a(n) ___________ fossil.

index

A fossil that is a very short-lived, geographically widespread species known to exist during a specific period of geologic time is a(n) ________ fossil.

index OR guide

The Great Unconformity ______.

is an angular unconformity represents 1.3 billion years

Dating rocks using radioactive isotopes that decay over time is called ___________ dating.

isotopic

When geologists assign actual numbers to the age of a rock unit, they determine the ________ age.

isotopic, absolute, radiometric, numerical, OR numeric

Finding several species of fossils, rather than just one, in the same rock layer is more useful to geologists because ______.

it indicates the sediments must have been deposited at the same time, when all the species were present

The instrument that is used to measure the ratios of parent to daughter products in a rock or mineral is called a ______.

mass spectrometer

On the Yucatán Peninsula, a ______ is evidence that a comet or asteroid is a possible cause of the dinosaurs' extinction at the end of the Mesozoic Era.

massive crater

Special rocks found in Antarctica are dated with isotopes to give an average age of Earth of 4.55 billion years. We can use these dark-colored _______ because scientists assume they were formed at the same time as Earth.

meteorites

When several species of fossils are found in adjacent layers, the time of formation of each rock layer can be assigned to a(n) _________ span of time.

narrow, shorter, specific, OR limited

When several species of fossils are found in adjacent layers, the time of formation of each rock layer can be assigned to a(n) ____________ span of time.

narrow, shorter, specific, OR limited

The oldest known rock found on Earth is dated at ______ years old.

nearly 4 billion

The term evolution is used in two ways. First, it refers to ______ in the fossil record; and second, it refers to tested explanations, known as evolutionary ______.

observed changes; theories

The principle of inclusion states that the clasts within a conglomerate are ________ than the conglomerate.

older

The principle of inclusion states that the clasts within a conglomerate are __________ than the conglomerate.

older

Let's assume the fossils in the tan bed are assigned an age of approximately 185 million years. How old is the unconformity?

older than 185 million years

This stratigraphic section from the Grand Canyon represents the ______ rocks there.

oldest

Petrified wood

organic matter replaced by silica or pyrite

insect in amber

organic matter trapped in tree sap

Geologists can tell that folded sedimentary rocks have been deformed by the principle of ________ __________.

original horizontality

Studies of Archean sedimentary rocks indicate that __________ gas was absent from Earth's atmosphere for most of the Archean.

oxygen

What gas was lacking in early Earth's atmosphere? Its absence played a strong role in the type of weathering and organisms on Earth's surface.

oxygen

Mass spectrometers are used by geologists to measure the ratios of _________ isotopes to __________ isotopes.

parent; daughter

In a desert environment, desert _______ and ______ can be used to determine the relative age of the land surface because they become more developed with time.

pavement; varnish

The three eras of the geologic timescale are divided into units called _________.

periods

The discovery of ______ allowed geologists to use isotopes to finally determine the age of Earth with accuracy.

radioactivity

Lord Kelvin's ideas about the loss of heat from Earth and determining the age of Earth were put to rest when _____________ was discovered. As radioactive elements decay, ___________ is given off. Not knowing about this additional source, Kelvin's estimate was much too young.

radioactivity; heat

Old sedimentary rocks that are __________ in color indicate the presence of oxygen in Earth's early atmosphere and oceans. (Use just one color for your answer.)

red

The fossil content in _________ rocks is an important tool in finding the correct sequences that trap oil and gas.

sedimentary

The Paleozoic rocks in the Grand Canyon are ______ rocks that are ______ oriented.

sedimentary; horizontally

Index fossils existed for a ______ time period so they are ______ useful assigning ages to rocks that contain them.

short; very

An index fossil is both ________-lived and occurs over a(n) ______ areal distribution.

short; wide

An impact crater is ______ if it is relatively small, while a(n) ______ crater is larger and has a central peak.

simple; complex

The study of sequences of rocks, including the rock types, fossils, and inferred environments, is ____________.

stratigraphy

The study of sequences of rocks, including the rock types, fossils, and inferred environments, is _____________.

stratigraphy

Geologists use the principle of faunal ___________, or how fossils change systematically over geologic time, to help identify specific time periods.

successions

Punctuated equilibrium is a hypothesis that explains how new characteristics in an organism, or organisms, appear ______

suddenly

The creation of an impact crater involves ______.

the transfer of kinetic energy the formation of a ring around the impact made of ejected material the shattering and melting of the impacted rocks

Early scientific attempts at determining Earth's age gave a number that was ______.

too young

True or false: An igneous dike will bake the surrounding rock, indicating that the dike is younger than the surrounding rock.

true

The erosional surface observed by James Hutton at Siccar Point in Scotland is now called a(n) ________ because it represents a significant amount of missing time in the geologic record.

unconformity

Rivers flowing over land and into the oceans provide the different salts for ocean waters. Early scientists attempted to use the salinity of rivers, the rate of water flow, and estimates of evaporation in the oceans to determine the age of Earth. However, their calculations did not take into account salt precipitated into rock layers, and the determined age was too ______.

young