Question

In the mid-nineteenth century, uniformitarian geology, championed by Charles Lyell, held that erratic boulders and scoured bedrock across Northern Europe were deposited by iceberg drift during a period of submerged continents. Lyell favored this "drift theory" primarily because it preserved his core postulate of gradual, steady-state geological change without invoking catastrophic events. However, when Louis Agassiz proposed in 1840 that expansive continental ice sheets had swept over the land, the scientific community initially dismissed his glacial theory as an unnecessary resurgence of catastrophism. To overcome this resistance, Agassiz pointed to contemporary Alpine glaciers, demonstrating that subglacial abrasion produces distinctive linear striations and unsorted till identical to the features observed across lowland Europe. By anchoring his argument in observable present-day processes, Agassiz skillfully turned uniformitarian logic back against Lyell's supporters. Nonetheless, the drift theory persisted for decades, largely because accepting Agassiz's paradigm required geologists to concede that global temperatures had dropped precipitously in the recent past—a climate anomaly that contemporary thermodynamic theories could not readily explain.

Which of the following best describes the rhetorical function of the sentence "By anchoring his argument in observable present-day processes, Agassiz skillfully turned uniformitarian logic back against Lyell's supporters" in the context of the passage as a whole?