Geos Chpt 9

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

Examine the image. Which number represents the oldest rocks?

1 Reason: Right! Original horizontality and superposition tell us the beds on the left are the oldest.

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 non-layered 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 sediments lithify

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

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

Adaptability to environmental change

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

Amphibians and early reptiles Coral reefs, insects, ferns Crinoids, molluscs, trilobites, snails

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

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

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

At the bottom Reason: This follows from the principle of superposition, which states that when a layer of sediment is deposited, any rock unit on which it rests must be older.

The mineralized granite intrusion shown can be dated by its relative age using the principle of _________ - _______ relations.

Blank 1: cross Blank 2: cutting

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

Blank 1: nonconformity Blank 2: disconformity

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

Blank 1: younger or newer Blank 2: cross Blank 3: cutting

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

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

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.

Carbon-14 (best for young materials) K-Ar Rb-Sr (best for old materials)

Match the isotopic system element(s) that could be used for dating with the correct geologic example. Instructions

Carbon-14 Charcoal incorporated into recent sediment. K-Ar A volcanic eruption. U-Pb A solidification of a granite.

The first humans appeared before 300,000 years ago in the _______.

Cenozoic

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

Cenozoic Mesozoic Paleozoic Precambrian

Match each geologic era with its meaning in the fossil record. Instructions

Cenozoic - Recent life. Mesozoic - Middle life. Paleozoic - Ancient life.

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

Charcoal Bones Wood

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

Charcoal Water Wood Shells

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

Chicxulub crater, Mexico Reason: This crater is the impact site of a massive comet or asteroid. Deccan Traps, India Reason: The Deccan Traps resulted from a massive outpouring of basaltic lava that would have choked the atmosphere with sulfur dioxide.

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

Contact effects Superposition

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

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.

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

Cyanobacteria Photosynthesis

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

Dendrites Concretions

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.

Deposition of sediments in layers (first) Lithification into sedimentary rocks 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.

Deposition of tan fossil-bearing layer. Land surface eroded, forming igneous pebbles. Cross-cutting dike intruded. Green shale and gray limestone deposited horizontally.

Match the relative dating principle or technique to the example of how scientists use it to study archeological sites.

Desert varnish: Rocks without this are used in relatively young constructions. Inclusions: Pieces of an older building are used in a younger building. Superposition: The oldest ruins are on the bottom.

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.

Devonian Mississippian Triassic Neogene

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

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

Dikes Fractures Veins

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

Dying

Match the time period within the Paleozoic Era with examples of the forms of life that existed on Earth.

Early Paleozoic: Sea life such are corals, crinoids, mollusks, trilobites, and snails were abundant. Middle Paleozoic: Fish became diverse and abundant in the ocean. 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

Match the geologic term related to lateral changes in rock type with its meaning in the list shown.

Facies change: Different sediments are deposited due to a change in the environment. Erosion: Missing rocks are marked by an unconformity. Restricted event: A deposit is of limited aerial extent. Change in thickness: River deposits become thinner at the edge of a valley.

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

False Reason: An angular unconformity forms above tilted layers.

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

False Reason: The granite had to be there first before the unconformity could cut across it.

_____ are evidence of ancient life in sedimentary rocks.

Fossils

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

Granite Nonlayered metamorphic rocks

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

Great

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

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?

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

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

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.

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

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

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

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.

Layers of sedimentary rocks are deposited horizontally. (first event) Rocks are folded into an anticline. Oil and gas are trapped by the fold. (last event)

What do geologists use to age correlate rocks?

Magnetic signatures Index fossil assemblages Isotopic ages on lava flows

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

Mesozoic

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

Nearly all Reason: Yes, it is over 99%.

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.

Neogene (most recent) Cretaceous Jurassic Triassic Devonian Cambrian (oldest)

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

Nonconformity

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

Nonlayered rocks are uplifted to the surface.

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

Match the term to its correct example.

Observed changes (evolution): Development of stronger front fins in Paleozoic fish occurred, as compared to fish fossils found in older rock layers. Evolutionary theory: Favorable genetic mutations occurring in a species are more successful in small, isolated populations than in large populations.

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

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

Which of the following are principles of relative dating?

Original horizontality Cross-cutting relations Superposition

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

Which three periods currently make up the Cenozoic?

Paleogene Quaternary Neogene

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

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

Paleozoic Mesozoic

Match the resulting fossil with its method of preservation.

Petrified wood - Organic matter replaced by silica or pyrite. Insect in amber - Organic matter trapped in tree sap. Dinosaur bones - Hard parts buried and preserved. Fish with fins and scales - Impressions on a lake bed. Fossil fern - Thin films of carbon on a rock surface.

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

Potassium-Argon

The chapter of geologic time that is represented by simpler life forms such as bacteria and algae is the _______. (Use just one word for your answer.)

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

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

Quaternary Neogene Paleogene

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

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

Which of the following statements about James Hutton are correct?

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 Worked in Scotland

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

Rocks are deposited horizontally. Rocks are folded. Uplift occurs, and folded rocks are eroded. Horizontal rocks are deposited over eroded tilt beds.

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

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

Which principle is used to determine the age of rocks by ordering them from oldest on the bottom to the youngest on the top?

Superposition

Match the principle of relative dating with its definition.

Superposition - The oldest rock is at the bottom. Cross-cutting relations - The fault is younger than the rocks is cuts across. Original horizontality - Sediments and volcanic units are usually deposited in flat-lying layers. Inclusions - Rocks may incorporate older pieces of rock. Contact effects - A baked zone forms next to a dike during intrusion.

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

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

The layered rocks are tilted and deformed.

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

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

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

There was oxygen.

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

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

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

Through photosynthesis by cyanobacteria

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

Tributaries

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

True

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

True Reason: Fossils are not just bones, but can include any physical indication of life. For example, dinosaur footprints are considered trace fossils.

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

True Reason: Geologists can use contact effects to help determine relative age.

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.

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 Reason: The rocks had to be there first before the river could cut the canyon.

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

Two great mass extinctions

Match the description of a group of dinosaurs with the correct examples. Instructions

Tyrannosaurus rex and Apatosaurus - Diverse group of carnivores and herbivores with hip structures similar to lizards Stegosaurus and Triceratops - Had birdlike hip structures and were herbivores

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.

Match the type of geologic hazard with the method that can be used to date when it last occurred. Instructions

Volcanic eruptions: Using isotopic methods, such as Ar-Ar dating. Earthquakes: Using cross-cutting relations to determine the age of the fault. Flooding: Using the amount of soil development and carbon-14 dating on terraces.

Who discovered the principle of faunal succession?

William Smith

The first organisms on Earth included ______.

algae

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

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

angular unconformity Reason: The underlying rocks were tilted before the formation of the erosion surface, making the unconformity an angular unconformity.

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

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, C-14, or carbon 14

Baking of rocks surrounding an igneous intrusion is called ________ effects.

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

When a geologist attempts to match up two different sections of rock according to time, he or she is _______ the rocks.

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

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

craters

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

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

cross-cutting, crosscutting, or cross cutting

About 2 billion years ago, ______ had produced enough oxygen through photosynthesis to form a protective layer of ozone in the atmosphere.

cyanobacteria

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

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

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

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

The vast majority of impact cratering occurred ______.

early in Earth's history

The geologic timescale is subdivided into three since the end of the Precambrian. (Use just one word for your answer.)

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 Reason: Evolution is the process through which species change over time, and new organisms may arise.

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

existed for a long period of geologic time

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

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.

faunal

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

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

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

fossils

Geologists use ______ to document evolution in the rock record.

fossils

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

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

groundwater or water

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

hard or solid

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

ice

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

Groundwater can be dated using ______.

isotopes

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

There were two types of dinosaur: those such as Tyrannosaurus rex that had hip structures similar to _______ and those such as Stegosaurus that had hip structures similar to ________.

lizards birds

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

long Reason: Isotopes that decay quickly and have a short half-life are appropriate for dating young rocks and archaeological artifacts.

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 Paleozoic and Mesozoic Eras both end with a(n) _____ ______.

mass extinction

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

The oldest rocks in the Grand Canyon are ______.

metamorphic plutonic Precambrian

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

metamorphosed ultramafic lava flows

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

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

nearly 4 billion

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

neutrons

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

not very

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 Reason: Evolutionary theories include the theory of natural selection.

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

of erosion restricted events that formed them a facies changes

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

older

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

oldest Reason: The Precambrian rocks are as old as 1.7 billion years.

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

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

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 or O2

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

parent daughter

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

periods

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

punctuated equilibrium

Isotopic dating allows scientists to assign numeric ages to rock using the natural _______ decay to certain isotopes.

radioactive

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 Great Unconformity ______.

represents 1.3 billion years is an angular unconformity

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

seas or oceans mountains

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

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

short widespread, large, wide, or broad

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

short; very

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

simple; complex

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

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

stratigraphy

Stratigraphy is the ______.

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

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 principle of _______ tells geologists that the oldest rock layer in the diagram is on the bottom; therefore, it was deposited first.

superposition

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

superposition

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

superposition

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

the Moon meteorites

Uniformitarianism can be stated as ______.

the present is the key to the past

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

too young

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 or impression

Subsidiary drainages on a river are known as ______.

tributaries

Buried erosion surfaces that represent large intervals of time are called

unconformities

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

"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

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 Reason: Desert pavement occurs when stones become concentrated on the surface over time, while finer materials wash or blow away.

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

varnish pavement

Zircons are used to date ______.

very old rocks

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

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

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

Superposition helps us to determine that the lava flow is than the underlying surface.

younger

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

zircon

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

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