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Difficulty: MediumEarth's History and Paleontology

A team of paleontologists discovers identical fossil specimens in thin sedimentary rock strata across three widely separated continents. Geological records show that this specific organism existed for only a brief interval of geologic time. Which of the following best describes the primary scientific value of this index fossil?

  1. A
    Proving that upper undisturbed rock layers are consistently older than deeper underlying strata
  2. B
    Demonstrating that the enclosing sedimentary strata formed from the rapid cooling and crystallization of volcanic magma
  3. Correlating and establishing the relative ages of distant rock layers across different geographic regionsAnswer
  4. D
    Indicating that the rock underwent severe recrystallization under extreme metamorphic heat and pressure

Answer

Correlating and establishing the relative ages of distant rock layers across different geographic regions
An index fossil must be easily recognizable, abundant, geographically widespread, and restricted to a short geologic time range. When geologists find the same index fossil in different locations, they can conclude that the corresponding rock layers formed during the same geologic period, enabling precise stratigraphic correlation.

Step-by-Step Solution

1
Identify the key defining characteristics of the fossil described in the scenario
The organism was geographically widespread (found on three continents) and existed for a short span of geologic time (confined to a thin stratum).
These are the diagnostic criteria that define an index fossil.
2
Determine how geologists utilize index fossils in stratigraphy
Because the organism only lived during one specific timeframe everywhere it existed, any rock layer containing it must have formed during that same time period.
This allows geologists to establish relative time equivalence across distant sedimentary formations.

Key Concept

Index fossils in stratigraphic correlation and relative dating
Estimated Time:1m 0s
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Topics

Earth's History and Paleontology

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