Geologic Time Framework - Middle School Earth and Space Science
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What does the law of superposition state for undisturbed sedimentary rock layers?
What does the law of superposition state for undisturbed sedimentary rock layers?
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Older layers are below younger layers. This fundamental principle helps determine relative ages in rock sequences.
Older layers are below younger layers. This fundamental principle helps determine relative ages in rock sequences.
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Which dating method gives a numerical age: relative dating or absolute dating?
Which dating method gives a numerical age: relative dating or absolute dating?
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Absolute dating. Relative dating only gives sequence; absolute dating provides years.
Absolute dating. Relative dating only gives sequence; absolute dating provides years.
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What is an era in geologic time?
What is an era in geologic time?
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A major subdivision of an eon. Eras typically last hundreds of millions of years, like the Mesozoic Era.
A major subdivision of an eon. Eras typically last hundreds of millions of years, like the Mesozoic Era.
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What is an eon in geologic time?
What is an eon in geologic time?
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The largest division of geologic time. Eons span billions of years, like the Phanerozoic Eon (541 million years ago to present).
The largest division of geologic time. Eons span billions of years, like the Phanerozoic Eon (541 million years ago to present).
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What is the correct order of units from smallest to largest: epoch, eon, era, period?
What is the correct order of units from smallest to largest: epoch, eon, era, period?
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Epoch, period, era, eon. Arranging from smallest to largest shows the hierarchical structure of geologic time.
Epoch, period, era, eon. Arranging from smallest to largest shows the hierarchical structure of geologic time.
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Which era is known for early life, including many marine organisms, before dinosaurs?
Which era is known for early life, including many marine organisms, before dinosaurs?
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Paleozoic Era. First era of Phanerozoic, 541-252 million years ago.
Paleozoic Era. First era of Phanerozoic, 541-252 million years ago.
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Which layer is oldest in an undisturbed sequence labeled top-to-bottom as A, B, C, D?
Which layer is oldest in an undisturbed sequence labeled top-to-bottom as A, B, C, D?
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Layer D. Superposition places oldest layers at bottom.
Layer D. Superposition places oldest layers at bottom.
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What are the four main units of the geologic time scale from largest to smallest?
What are the four main units of the geologic time scale from largest to smallest?
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Eon, era, period, epoch. These hierarchical divisions help organize Earth's vast history into manageable units.
Eon, era, period, epoch. These hierarchical divisions help organize Earth's vast history into manageable units.
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What is the geologic time scale?
What is the geologic time scale?
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A timeline that organizes Earth's history using rock layers and fossils. Scientists use rock layers and fossils to organize Earth's 4.6 billion year history.
A timeline that organizes Earth's history using rock layers and fossils. Scientists use rock layers and fossils to organize Earth's 4.6 billion year history.
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Which is most likely to mark a new geologic period: a local flood or a global mass extinction?
Which is most likely to mark a new geologic period: a local flood or a global mass extinction?
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A global mass extinction. Global events like mass extinctions create worldwide markers in the rock record.
A global mass extinction. Global events like mass extinctions create worldwide markers in the rock record.
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What kind of evidence most often defines boundaries between geologic time units?
What kind of evidence most often defines boundaries between geologic time units?
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Major changes in fossils, including mass extinctions and appearances. Life's evolution and extinction events provide clear markers for time boundaries.
Major changes in fossils, including mass extinctions and appearances. Life's evolution and extinction events provide clear markers for time boundaries.
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What is correlation in stratigraphy?
What is correlation in stratigraphy?
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Matching rock layers of the same age across different locations. Geologists use fossils and rock properties to link separated rock units.
Matching rock layers of the same age across different locations. Geologists use fossils and rock properties to link separated rock units.
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What is an index fossil?
What is an index fossil?
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A widespread, short-lived fossil used to date and correlate rock layers. These fossils existed globally for brief periods, making them excellent time markers.
A widespread, short-lived fossil used to date and correlate rock layers. These fossils existed globally for brief periods, making them excellent time markers.
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If a fault cuts across rock layers, what is the relative age of the fault?
If a fault cuts across rock layers, what is the relative age of the fault?
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The fault is younger than the layers it cuts. Cross-cutting relationships show the fault formed after the layers it disrupts.
The fault is younger than the layers it cuts. Cross-cutting relationships show the fault formed after the layers it disrupts.
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What does the principle of cross-cutting relationships state?
What does the principle of cross-cutting relationships state?
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A feature that cuts rock is younger than the rock it cuts. This principle helps determine relative ages of faults, intrusions, and erosion.
A feature that cuts rock is younger than the rock it cuts. This principle helps determine relative ages of faults, intrusions, and erosion.
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What does the principle of original horizontality state?
What does the principle of original horizontality state?
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Sedimentary layers are deposited in nearly horizontal layers. Gravity causes sediments to settle horizontally when first deposited.
Sedimentary layers are deposited in nearly horizontal layers. Gravity causes sediments to settle horizontally when first deposited.
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In an undisturbed sequence, which layer is oldest: top, middle, or bottom?
In an undisturbed sequence, which layer is oldest: top, middle, or bottom?
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Bottom layer. Superposition places oldest rocks at the bottom of undisturbed sequences.
Bottom layer. Superposition places oldest rocks at the bottom of undisturbed sequences.
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What is absolute dating in geology?
What is absolute dating in geology?
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Determining a numerical age, often using radioactive decay. Radioactive isotopes decay at known rates, providing specific ages in years.
Determining a numerical age, often using radioactive decay. Radioactive isotopes decay at known rates, providing specific ages in years.
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What is relative dating in geology?
What is relative dating in geology?
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Determining which rocks or events are older or younger without exact ages. Uses principles like superposition to sequence events without specific dates.
Determining which rocks or events are older or younger without exact ages. Uses principles like superposition to sequence events without specific dates.
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What is an epoch in geologic time?
What is an epoch in geologic time?
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A subdivision of a period. Epochs are the smallest standard divisions, lasting millions of years.
A subdivision of a period. Epochs are the smallest standard divisions, lasting millions of years.
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What is a period in geologic time?
What is a period in geologic time?
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A subdivision of an era. Periods last tens of millions of years, like the Jurassic Period.
A subdivision of an era. Periods last tens of millions of years, like the Jurassic Period.
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A dike cuts across layers X, Y, and Z. Which is younger: the dike or the layers it cuts?
A dike cuts across layers X, Y, and Z. Which is younger: the dike or the layers it cuts?
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The dike is younger. Cross-cutting principle: intrusions postdate what they cut.
The dike is younger. Cross-cutting principle: intrusions postdate what they cut.
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Which dating method is most appropriate to determine the age of a volcanic ash layer in years?
Which dating method is most appropriate to determine the age of a volcanic ash layer in years?
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Absolute (radiometric) dating. Volcanic minerals contain radioactive isotopes for dating.
Absolute (radiometric) dating. Volcanic minerals contain radioactive isotopes for dating.
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Which era is known for the rise and diversification of mammals after dinosaurs went extinct?
Which era is known for the rise and diversification of mammals after dinosaurs went extinct?
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Cenozoic Era. Current era beginning 66 million years ago.
Cenozoic Era. Current era beginning 66 million years ago.
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What term describes Earth’s entire history from formation to the present?
What term describes Earth’s entire history from formation to the present?
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Geologic time. Spans 4.6 billion years from Earth's formation to today.
Geologic time. Spans 4.6 billion years from Earth's formation to today.
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