Faunal succession recognized in the sequence of fossils in stratified sedimentary rocks was a key concept that led to

Faunal succession recognised in the sequence of fossils in stratified sedimentary rocks was a key concept that led to the determination ages of rock and strata.

Explanation:

The faunal succession with these determining ages thus helped in the course evaluation of evolution. This therefore, conceptualises the pattern of evolution found for the life and earth.

The different period of times had variety of fossils which got stratified in different strata. Those strata studied can be taken out in a reliable order of earliest strata at the bottom with newer on top. This concept was principled by William Smith.

i'm sure the answer you are looking for would be

a. an ice age

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