What is an index fossil?(1 point)
A. a fossil of a footprint or other trace made by an organism
B. a fossil in igneous rock
C. a fossil of an organism from a species that did not live for very long
D. a fossil left during a mass extinction event
C. a fossil of an organism from a species that did not live for very long.
The correct answer is C. A. a fossil of an organism from a species that did not live for very long.
Index fossils are used by paleontologists to determine the relative age of rock layers in a technique called biostratigraphy. These fossils are typically from species that had a short existence on Earth but were widespread and abundant during that time. They act as markers for specific time periods in Earth's history.
To arrive at this answer, you can eliminate options A, B, and D by understanding the definitions and characteristics of each term. Option A, a fossil of a footprint or trace, is incorrect because index fossils are typically the actual remains of organisms, not footprints or traces. Option B, a fossil in igneous rock, is also incorrect because index fossils are found in sedimentary rock, not igneous rock. Option D, a fossil left during a mass extinction event, is incorrect because index fossils are not necessarily associated with mass extinctions but with specific time periods within the fossil record. Therefore, the correct answer is C, which accurately describes the characteristics of an index fossil.