Question

The following passage is adapted from an essay on nineteenth-century geological science:

For much of the early nineteenth century, European geologists accounted for "erratics"—gigantic, isolated boulders deposited far from their parent rock formations—by appealing to catastrophic marine deluges. This prevailing deluge hypothesis offered a satisfying synthesis for scholars of the era: it reconciled traditional narratives with observable landscape features while requiring no radical reevaluation of Earth's climate history. Consequently, when Swiss naturalist Louis Agassiz presented his alternative theory of continental glaciation in 1837, proposing that massive ice sheets had once carpeted Europe, the initial reaction from the scientific establishment was sharp disdain. Dominant figures of the era argued that moving ice across hundreds of miles of flat terrain violated known physical laws, treating Agassiz's proposal as an eccentric detour from established principles.

In the 1840s, however, the discourse surrounding Agassiz's work underwent a marked shift. As Agassiz and his supporters amassed precise field measurements—cataloging parallel striations carved into granite bedrock and mapping the distinct arc-shaped moraines left by retreating glaciers—the scientific conversation moved away from ideological attacks on Agassiz's credibility. Scholars stopped arguing over whether continental ice was theoretically plausible and turned instead to investigating the precise mechanics of glacial motion and sediment deposition. Consequently, the debate evolved from a contentious dispute over competing origin narratives into a collaborative, empirical effort to map the extent of past glaciation.

Which of the following best describes the structural shift that occurs between the first paragraph and the second paragraph?