Rock Layers Show History - Middle School Earth and Space Science
Card 1 of 25
Which unconformity type is an erosional gap between parallel sedimentary layers?
Which unconformity type is an erosional gap between parallel sedimentary layers?
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Disconformity. The erosion surface separates two parallel sedimentary rock sequences.
Disconformity. The erosion surface separates two parallel sedimentary rock sequences.
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What is the principle of original horizontality in sedimentary strata?
What is the principle of original horizontality in sedimentary strata?
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Sedimentary layers are deposited in nearly horizontal layers. Gravity causes sediments to settle flat when deposited in water or air.
Sedimentary layers are deposited in nearly horizontal layers. Gravity causes sediments to settle flat when deposited in water or air.
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What is the main difference between relative dating and absolute dating?
What is the main difference between relative dating and absolute dating?
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Relative: order of events; Absolute: numerical age in years. Relative dating sequences events; absolute dating provides specific ages.
Relative: order of events; Absolute: numerical age in years. Relative dating sequences events; absolute dating provides specific ages.
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What two traits make a fossil most useful as an index fossil?
What two traits make a fossil most useful as an index fossil?
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Wide geographic range and short time range. Widespread but short-lived species best mark specific times.
Wide geographic range and short time range. Widespread but short-lived species best mark specific times.
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Identify the relative ages: Layer A is cut by Fault F. Which is younger, A or F?
Identify the relative ages: Layer A is cut by Fault F. Which is younger, A or F?
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Fault F is younger than Layer A. Cross-cutting principle: the fault formed after Layer A existed.
Fault F is younger than Layer A. Cross-cutting principle: the fault formed after Layer A existed.
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Identify the relative ages: Igneous Dike D cuts layers B and C. Which is oldest, D or C?
Identify the relative ages: Igneous Dike D cuts layers B and C. Which is oldest, D or C?
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Layer C is older than Dike D. The dike intruded after Layer C formed, making C older.
Layer C is older than Dike D. The dike intruded after Layer C formed, making C older.
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What two key traits make a fossil an effective index fossil?
What two key traits make a fossil an effective index fossil?
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Short time range and wide geographic distribution. These traits ensure the fossil marks a specific, brief time period globally.
Short time range and wide geographic distribution. These traits ensure the fossil marks a specific, brief time period globally.
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Identify what a ripple-marked sandstone layer most directly indicates about past conditions.
Identify what a ripple-marked sandstone layer most directly indicates about past conditions.
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Moving water or wind at the time of deposition. Ripples form from flowing water or wind moving sediment particles.
Moving water or wind at the time of deposition. Ripples form from flowing water or wind moving sediment particles.
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Identify what mud cracks preserved in a rock layer most directly indicate about the past.
Identify what mud cracks preserved in a rock layer most directly indicate about the past.
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Wet sediment dried and shrank after exposure to air. Mud cracks form when wet mud dries out, creating polygonal patterns.
Wet sediment dried and shrank after exposure to air. Mud cracks form when wet mud dries out, creating polygonal patterns.
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Identify the event most directly recorded by a layer containing unsorted, mixed-size sediment.
Identify the event most directly recorded by a layer containing unsorted, mixed-size sediment.
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Rapid deposition by ice (glacier) or a high-energy mass flow. Poor sorting indicates rapid deposition without size separation by water.
Rapid deposition by ice (glacier) or a high-energy mass flow. Poor sorting indicates rapid deposition without size separation by water.
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Which event is indicated by a fault that offsets several sedimentary layers?
Which event is indicated by a fault that offsets several sedimentary layers?
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Faulting occurred after the youngest offset layer formed. Cross-cutting principle: the fault is younger than all layers it cuts.
Faulting occurred after the youngest offset layer formed. Cross-cutting principle: the fault is younger than all layers it cuts.
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Identify the relative age: pebbles of basalt are inside a conglomerate; which is older, basalt or conglomerate?
Identify the relative age: pebbles of basalt are inside a conglomerate; which is older, basalt or conglomerate?
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The basalt pebbles are older. Principle of inclusions: fragments predate the rock containing them.
The basalt pebbles are older. Principle of inclusions: fragments predate the rock containing them.
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Which conclusion is supported if the same index fossil is found in two separated rock layers?
Which conclusion is supported if the same index fossil is found in two separated rock layers?
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The layers are the same relative age (correlated in time). Index fossils indicate simultaneous deposition in different locations.
The layers are the same relative age (correlated in time). Index fossils indicate simultaneous deposition in different locations.
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Identify the event: Sedimentary layers are tilted and then overlain by horizontal layers. What occurred between them?
Identify the event: Sedimentary layers are tilted and then overlain by horizontal layers. What occurred between them?
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Tilting, uplift, and erosion occurred before new deposition. Angular unconformity shows tectonic activity between depositions.
Tilting, uplift, and erosion occurred before new deposition. Angular unconformity shows tectonic activity between depositions.
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Identify the past event suggested by mud cracks preserved in a rock layer.
Identify the past event suggested by mud cracks preserved in a rock layer.
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Sediment dried after exposure to air. Wet mud shrinks and cracks when exposed and dried.
Sediment dried after exposure to air. Wet mud shrinks and cracks when exposed and dried.
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Which option is older: a sedimentary layer or an igneous dike that cuts across it?
Which option is older: a sedimentary layer or an igneous dike that cuts across it?
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The sedimentary layer is older. Cross-cutting principle: the dike cuts existing rock.
The sedimentary layer is older. Cross-cutting principle: the dike cuts existing rock.
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Identify the relative age: an igneous dike cuts across sedimentary layers. Which is younger?
Identify the relative age: an igneous dike cuts across sedimentary layers. Which is younger?
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The igneous dike is younger than the sedimentary layers it cuts. The dike intruded after the sedimentary layers were already present.
The igneous dike is younger than the sedimentary layers it cuts. The dike intruded after the sedimentary layers were already present.
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What principle states that a geologic feature cutting across layers is younger than the layers it cuts?
What principle states that a geologic feature cutting across layers is younger than the layers it cuts?
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Principle of cross-cutting relationships. Features must exist before they can be cut through.
Principle of cross-cutting relationships. Features must exist before they can be cut through.
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Identify the event order: If a fault cuts across Layers A, B, and C, which formed last: the fault or the layers?
Identify the event order: If a fault cuts across Layers A, B, and C, which formed last: the fault or the layers?
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The fault formed last. Cross-cutting principle: the fault cuts existing layers.
The fault formed last. Cross-cutting principle: the fault cuts existing layers.
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Identify the older feature: A basalt dike cuts through limestone. Which is older, the dike or the limestone?
Identify the older feature: A basalt dike cuts through limestone. Which is older, the dike or the limestone?
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The limestone is older. Cross-cutting principle: the dike intruded after limestone formed.
The limestone is older. Cross-cutting principle: the dike intruded after limestone formed.
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Identify the missing-time clue: What feature indicates erosion or nondeposition between two rock layers?
Identify the missing-time clue: What feature indicates erosion or nondeposition between two rock layers?
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An unconformity. Represents a gap in the geologic record between rock units.
An unconformity. Represents a gap in the geologic record between rock units.
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Which unconformity forms when sedimentary rock overlies eroded igneous or metamorphic rock?
Which unconformity forms when sedimentary rock overlies eroded igneous or metamorphic rock?
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Nonconformity. Forms when sediments deposit on eroded crystalline basement rocks.
Nonconformity. Forms when sediments deposit on eroded crystalline basement rocks.
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Which unconformity forms between parallel sedimentary layers with an erosional surface?
Which unconformity forms between parallel sedimentary layers with an erosional surface?
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Disconformity. Parallel layers with time gap show erosion without tilting.
Disconformity. Parallel layers with time gap show erosion without tilting.
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What is an index fossil, and what is it used for in rock strata?
What is an index fossil, and what is it used for in rock strata?
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A widespread, short-lived fossil used to correlate and date layers. Their brief existence helps match layers from different locations.
A widespread, short-lived fossil used to correlate and date layers. Their brief existence helps match layers from different locations.
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What is the key idea of faunal succession used in interpreting rock strata?
What is the key idea of faunal succession used in interpreting rock strata?
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Fossil assemblages follow a predictable order through rock layers. Species appear and disappear in consistent sequence through time.
Fossil assemblages follow a predictable order through rock layers. Species appear and disappear in consistent sequence through time.
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