Read the following passage and evaluate the statement below.
In the early nineteenth century, geologist Charles Lyell revolutionized stratigraphy by classifying Tertiary rock layers based not on their mineral composition, but on their fossilized biological content. Before Lyell, geologists struggled to correlate rock formations across different geographical regions because local environmental conditions drastically altered mineral compositions. Sandstone in one region might be strictly contemporaneous with limestone in another, despite their radically different physical appearances.
By shifting the diagnostic criterion to fossil assemblages, Lyell provided a universal chronological key. Specifically, Lyell categorized these strata according to the proportion of fossilized marine mollusk species they contained that were still living in the present day. He divided the Tertiary period into three main epochs: the Eocene, the Miocene, and the Pliocene. The Eocene, representing the oldest strata, was defined by having only about 3.5 percent of its fossil mollusks belonging to extant species. The Miocene contained roughly 18 percent extant species. The most recent epoch, the Pliocene, was characterized by having a majority—often over 50 percent—of its fossil mollusks matching species that still survived.
This method relied on a crucial assumption regarding the stability of evolutionary change: Lyell's percentages assumed that the rate at which marine species went extinct was relatively uniform across all different marine environments globally. The system initially struggled to account for localized anomalies, such as an isolated basin where a sudden change in water temperature might wipe out a vast number of native mollusk species without affecting global populations.
Statement: Based on the passage, a rock stratum in which approximately 96.5 percent of the fossilized mollusk species are now extinct would most likely be classified under Lyell's system as belonging to the Eocene epoch.
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