Fossils Show Relative Age - Middle School Earth and Space Science
Card 1 of 25
Which relative dating principle states that sedimentary layers are deposited in flat, horizontal sheets?
Which relative dating principle states that sedimentary layers are deposited in flat, horizontal sheets?
Tap to reveal answer
Original horizontality. Gravity and water deposit sediments horizontally before tilting occurs.
Original horizontality. Gravity and water deposit sediments horizontally before tilting occurs.
← Didn't Know|Knew It →
Which relative dating principle states that rock layers extend until they thin out or are cut off?
Which relative dating principle states that rock layers extend until they thin out or are cut off?
Tap to reveal answer
Lateral continuity. Sediments spread laterally until barriers or thinning stops deposition.
Lateral continuity. Sediments spread laterally until barriers or thinning stops deposition.
← Didn't Know|Knew It →
Which principle states that a rock layer or fault cutting another rock is younger than what it cuts?
Which principle states that a rock layer or fault cutting another rock is younger than what it cuts?
Tap to reveal answer
Cross-cutting relationships. Something must exist before it can be cut through by another feature.
Cross-cutting relationships. Something must exist before it can be cut through by another feature.
← Didn't Know|Knew It →
What is the relative age rule for inclusions (rock fragments) inside an igneous or sedimentary rock?
What is the relative age rule for inclusions (rock fragments) inside an igneous or sedimentary rock?
Tap to reveal answer
Inclusions are older than the rock that contains them. Rock fragments must exist before being incorporated into new rock.
Inclusions are older than the rock that contains them. Rock fragments must exist before being incorporated into new rock.
← Didn't Know|Knew It →
What is a fossil assemblage in a rock layer?
What is a fossil assemblage in a rock layer?
Tap to reveal answer
The group of different fossil species found together in one layer. Multiple species living together provide a time-specific fingerprint.
The group of different fossil species found together in one layer. Multiple species living together provide a time-specific fingerprint.
← Didn't Know|Knew It →
What is the best relative-age conclusion if two rock layers contain the same index fossil species?
What is the best relative-age conclusion if two rock layers contain the same index fossil species?
Tap to reveal answer
They are the same relative age (correlated in time). Index fossils mark specific time periods across different locations.
They are the same relative age (correlated in time). Index fossils mark specific time periods across different locations.
← Didn't Know|Knew It →
What does it mean if two rock layers contain the same index fossil species?
What does it mean if two rock layers contain the same index fossil species?
Tap to reveal answer
They are the same relative age. Index fossils represent specific time periods, so matching fossils = matching ages.
They are the same relative age. Index fossils represent specific time periods, so matching fossils = matching ages.
← Didn't Know|Knew It →
What is a fossil assemblage?
What is a fossil assemblage?
Tap to reveal answer
A group of different fossil species found together in one layer. Multiple species together provide more precise dating than single fossils.
A group of different fossil species found together in one layer. Multiple species together provide more precise dating than single fossils.
← Didn't Know|Knew It →
What is an unconformity in the rock record, and what does it indicate about time?
What is an unconformity in the rock record, and what does it indicate about time?
Tap to reveal answer
A surface of missing rock layers; it represents missing time. Erosion or non-deposition creates gaps in the geologic record.
A surface of missing rock layers; it represents missing time. Erosion or non-deposition creates gaps in the geologic record.
← Didn't Know|Knew It →
What type of fossil is most useful for determining the relative age of rock layers over wide areas?
What type of fossil is most useful for determining the relative age of rock layers over wide areas?
Tap to reveal answer
Index fossil. These fossils existed briefly but spread widely, making them time markers.
Index fossil. These fossils existed briefly but spread widely, making them time markers.
← Didn't Know|Knew It →
What two key traits must a fossil species have to be a good index fossil?
What two key traits must a fossil species have to be a good index fossil?
Tap to reveal answer
Wide geographic range and short geologic time range. Wide range ensures correlation; short time span provides precise dating.
Wide geographic range and short geologic time range. Wide range ensures correlation; short time span provides precise dating.
← Didn't Know|Knew It →
Which type of fossil is most useful for matching rock layers between different locations?
Which type of fossil is most useful for matching rock layers between different locations?
Tap to reveal answer
Index fossil. Their short time range and wide distribution enable precise correlation.
Index fossil. Their short time range and wide distribution enable precise correlation.
← Didn't Know|Knew It →
Identify the correct conclusion: Layer A is below Layer B in undisturbed strata. Which is older?
Identify the correct conclusion: Layer A is below Layer B in undisturbed strata. Which is older?
Tap to reveal answer
Layer A is older than Layer B. Superposition principle: lower layers formed before upper layers.
Layer A is older than Layer B. Superposition principle: lower layers formed before upper layers.
← Didn't Know|Knew It →
Identify the correct conclusion: A fault cuts across Layers C, D, and E. Which is younger, the fault or the layers?
Identify the correct conclusion: A fault cuts across Layers C, D, and E. Which is younger, the fault or the layers?
Tap to reveal answer
The fault is younger than Layers C, D, and E. Cross-cutting principle: the cutter is younger than what it cuts.
The fault is younger than Layers C, D, and E. Cross-cutting principle: the cutter is younger than what it cuts.
← Didn't Know|Knew It →
Identify the correct conclusion: Igneous dike X cuts through sedimentary Layer F. Which formed later?
Identify the correct conclusion: Igneous dike X cuts through sedimentary Layer F. Which formed later?
Tap to reveal answer
Dike X formed later than Layer F. The dike intruded after Layer F already existed.
Dike X formed later than Layer F. The dike intruded after Layer F already existed.
← Didn't Know|Knew It →
Identify the correct conclusion: Pebbles of Rock G are found inside Conglomerate H. Which is older?
Identify the correct conclusion: Pebbles of Rock G are found inside Conglomerate H. Which is older?
Tap to reveal answer
Rock G is older than Conglomerate H. Inclusion principle: fragments predate the rock containing them.
Rock G is older than Conglomerate H. Inclusion principle: fragments predate the rock containing them.
← Didn't Know|Knew It →
Which option best indicates an index fossil: A) long-lived species B) widespread, short-lived species?
Which option best indicates an index fossil: A) long-lived species B) widespread, short-lived species?
Tap to reveal answer
B) Widespread, short-lived species. Short lifespan provides precise time correlation across regions.
B) Widespread, short-lived species. Short lifespan provides precise time correlation across regions.
← Didn't Know|Knew It →
Identify the correct conclusion: Layer J contains Fossil Q; Layer K also contains Fossil Q. How do J and K compare in age?
Identify the correct conclusion: Layer J contains Fossil Q; Layer K also contains Fossil Q. How do J and K compare in age?
Tap to reveal answer
Layers J and K are the same relative age. Same index fossil indicates contemporaneous deposition.
Layers J and K are the same relative age. Same index fossil indicates contemporaneous deposition.
← Didn't Know|Knew It →
Identify the relative age: A volcanic ash layer lies between fossil layers M (below) and N (above). Which fossil layer is younger?
Identify the relative age: A volcanic ash layer lies between fossil layers M (below) and N (above). Which fossil layer is younger?
Tap to reveal answer
Layer N is younger than Layer M. Superposition applies: N is above M, so N is younger.
Layer N is younger than Layer M. Superposition applies: N is above M, so N is younger.
← Didn't Know|Knew It →
Which fossil evidence best supports that two separated outcrops formed during the same time period?
Which fossil evidence best supports that two separated outcrops formed during the same time period?
Tap to reveal answer
They share the same index fossil species. Index fossils provide time correlation between distant locations.
They share the same index fossil species. Index fossils provide time correlation between distant locations.
← Didn't Know|Knew It →
What is the best relative-age interpretation if a layer contains only modern species fossils and no extinct species fossils?
What is the best relative-age interpretation if a layer contains only modern species fossils and no extinct species fossils?
Tap to reveal answer
It is relatively young compared with layers containing extinct species. Modern species haven't had time to become extinct yet.
It is relatively young compared with layers containing extinct species. Modern species haven't had time to become extinct yet.
← Didn't Know|Knew It →
Find the relative order: Layer 1 has fossil K; Layer 2 above it has fossil L. K is known to appear earlier than L.
Find the relative order: Layer 1 has fossil K; Layer 2 above it has fossil L. K is known to appear earlier than L.
Tap to reveal answer
Layer 1 is older than Layer 2. Fossil succession shows K predates L, confirming superposition order.
Layer 1 is older than Layer 2. Fossil succession shows K predates L, confirming superposition order.
← Didn't Know|Knew It →
Which option best supports correlation: both layers contain species A and B together, or both contain only species A?
Which option best supports correlation: both layers contain species A and B together, or both contain only species A?
Tap to reveal answer
Both layers contain species A and B together. Multiple matching species provide stronger correlation than single species.
Both layers contain species A and B together. Multiple matching species provide stronger correlation than single species.
← Didn't Know|Knew It →
Identify the best evidence for same age: same rock color, same mineral grains, or same index fossil?
Identify the best evidence for same age: same rock color, same mineral grains, or same index fossil?
Tap to reveal answer
Same index fossil. Fossils are time-specific; rock properties vary by local conditions.
Same index fossil. Fossils are time-specific; rock properties vary by local conditions.
← Didn't Know|Knew It →
Which conclusion is valid: two layers share a fossil assemblage, but their rock types differ?
Which conclusion is valid: two layers share a fossil assemblage, but their rock types differ?
Tap to reveal answer
They can still be the same relative age. Rock type varies by environment, but fossils indicate time period.
They can still be the same relative age. Rock type varies by environment, but fossils indicate time period.
← Didn't Know|Knew It →