Geologic History flashcards

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What is meant by “Superposition” in this lesson?Relative dating: In an undisturbed sedimentary sequence, lower layers were deposited before layers above them.
What is meant by “Original horizontality” in this lesson?Relative dating: Sediments are generally deposited approximately horizontally, so later tilting implies subsequent change.
What is meant by “Cross-cutting relationship” in this lesson?Relative dating: A feature cutting another geological feature is younger than the feature it cuts.
What is meant by “Inclusion” in this lesson?Relative dating: A rock fragment enclosed within another rock existed before the enclosing rock formed.
What is meant by “Unconformity” in this lesson?Relative dating: An unconformity represents missing time caused by erosion or nondeposition.
What is meant by “Relative chronology” in this lesson?Relative dating: Relative chronology orders events without necessarily determining their numerical ages.
What is meant by “Fossil” in this lesson?Fossils: A fossil is preserved evidence of past life, including remains or activity traces.
What is meant by “Trace fossil” in this lesson?Fossils: A trace fossil records an organism's activity rather than its body.
What is meant by “Index fossil” in this lesson?Fossils: A useful index fossil has broad geographical occurrence and a relatively limited time range.
What is meant by “Preservation bias” in this lesson?Fossils: Organisms and environments differ in their likelihood of leaving recoverable fossils.
What is meant by “Paleoenvironment” in this lesson?Fossils: A paleoenvironment is a past environment inferred from multiple geological and biological clues.
What is meant by “Extinction” in this lesson?Fossils: Extinction occurs when a lineage has no surviving members, though the fossil record may be incomplete.
What is meant by “Radioactive decay” in this lesson?Absolute dating and geologic time: Unstable isotopes transform at statistically predictable rates into other nuclei.
What is meant by “Half-life” in this lesson?Absolute dating and geologic time: A half-life is the time required for half of a large population of parent atoms to decay.
What is meant by “Closed system” in this lesson?Absolute dating and geologic time: A closed dating system has not significantly gained or lost relevant parent or daughter material since the dated event.
What is meant by “Dating-event distinction” in this lesson?Absolute dating and geologic time: A numerical age dates a specific geological event rather than automatically every event affecting the rock.
What is meant by “Isotope suitability” in this lesson?Absolute dating and geologic time: An isotope system must have a useful half-life and suitable sample material for the age range.
What is meant by “Geologic time scale” in this lesson?Absolute dating and geologic time: The geologic time scale organizes Earth's history using geological and biological evidence and numerical constraints.