Chapter 10: Deep Time: How old is time flashcards |

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Cambrian explosion

The remarkable diversification of life, indicated by the fossil record, that occurred at the beginning of the Cambrian Period.

carbon-14 (14C) dating

A radiometric dating process that can tell us the age of organic material containing carbon originally extracted from the atmosphere.


The boundary surface between two rock bodies (as between two stratigraphic formations, between an igneous intrusion and adjacent rock, between two igneous rock bodies, or between rocks juxtaposed by a fault).


The process of defining the age relations between the strata at one locality and the strata at another.

cross-cutting relations

A means of determining the relative age of rock by looking at which rock or structure cuts another; the feature that has been cut is older.

daughter isotope

The decay product of radioactive decay.


The largest subdivision of geologic time.


An interval of geologic time representing the largest subdivision of a period.


An interval of geologic time representing the largest subdivision of the Phanerozoic Eon.

fossil succession

The principle that the assemblage of fossil species in a given sequence of sedimentary strata differs from that found in older sequences or in younger sequences; a given species appears at a certain level and then disappears (goes extinct) at a higher level.

geologic column

A composite stratigraphic chart that represents the entirety of the Earth's history.

geologic map

A map showing the distribution of rock units and structures across a region.

geologic time

The span of time since the formation of the Earth.

geologic time scale

A scale that describes the intervals of geologic time.


The time it takes for half of a group of a radioactive element's isotopes to decay.


Different versions of a given element that have the same atomic number but different atomic weights.

isotopic dating

The science of dating geologic events in years by measuring the ratio of parent radioactive atoms to daughter product atoms.

numerical age

The age of a rock or structure as specified in years; referred to as ร’absolute ageร“ in older literature.

original horizontality

The principle that sediments are deposited in nearly horizontal layers.

parent isotope

A radioactive isotope that undergoes decay.


An interval of geologic time representing a subdivision of a geologic era.


The interval of geologic time between Earth's formation about 4.57 Ga and the beginning of the Phanerozoic Eon 542 Ma.

radioactive decay

The process by which a radioactive atom undergoes fission or releases particles thereby transforming into a element.

relative age

The age of one geologic feature with respect to another.

stratigraphic column

A cross-section diagram of a sequence of strata summarizing information about the sequence.

stratigraphic formation

A recognizable layer of a specific sedimentary rock type or set of rock types, deposited during a certain time interval, that can be traced over a broad region.


The principle that younger layers of sediment are deposited on older layers of sediment; thus, in a sequence of strata, the oldest layer is at the base.


A boundary between two different rock sequences representing an interval of time during which strata were not deposited and/or were eroded.


The principle that the same physical processes observed today are responsible for the formation of ancient geologic features.

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