Question

Passage:

The enduring debate over the geomorphological origins of coral atolls—ring-shaped coral reefs enclosing a lagoon—sparked one of the most vigorous scientific controversies of the late nineteenth and early twentieth centuries. The foundational paradigm was established by Charles Darwin in 1842. Formulated during the voyage of the Beagle, Darwin's "subsidence theory" posited that coral atolls represent the final stage of a continuous evolutionary process driven by tectonic activity. He argued that as a volcanic island slowly subsides into the ocean over geological time, the fringing reef surrounding it grows upward to maintain proximity to the sunlit surface, eventually becoming a barrier reef and, once the central island completely submerges, a ring-like atoll. The elegance of Darwin's mechanism earned widespread initial acceptance, but it soon faced formidable challenges as oceanic exploration expanded.

In the 1880s, the Scottish oceanographer John Murray, relying on data gathered during the Challenger expedition, proposed a starkly different model that eschewed tectonic subsidence. Murray’s "pelagic theory" (also known as the solution theory) suggested that coral reefs could establish themselves on stationary submarine elevations—such as submerged volcanic peaks or plateaus built up by the continuous accumulation of pelagic sediment. Once the reef reached the surface, Murray theorized, its outward expansion was fueled by the abundant food supply in the open ocean, while the inner portion of the reef dissolved due to the solvent action of seawater heavily laden with carbon dioxide, thereby excavating the central lagoon.

A few decades later, the American marine biologist Alexander Agassiz mounted another sustained critique of Darwinian subsidence. Drawing on extensive surveys across the Pacific and the Caribbean, Agassiz argued that the varied topography of reef structures could not be explained by a single, uniform process of tectonic sinking. Instead, he advanced the "erosion theory," asserting that many atolls and barrier reefs were formed not by subsidence, but by the mechanical erosion of preexisting limestone platforms. According to Agassiz, oceanic currents and relentless wave action scoured the centers of these platforms to form lagoons, while corals subsequently colonized the elevated rims.

The debate shifted dramatically again with Reginald Daly’s introduction of the "glacial-control theory" in 1915. Daly recognized that the Pleistocene epochs, characterized by massive continental glaciations, would have caused significant global fluctuations in sea level. He hypothesized that during glacial maximums, sea levels dropped precipitously, exposing existing islands and reefs to severe subaerial erosion, effectively truncating them into flat, submerged platforms. As the glaciers melted and sea levels subsequently rose, coral colonies established themselves on the outer edges of these platforms, growing vertically in tandem with the rising waters to form atolls, thus rendering tectonic subsidence unnecessary to account for atoll morphology.

Question:
Based on the passage, match each of the following scientists to the precise geomorphological mechanism they proposed to explain the structural formation of coral atolls.