The main, or central, idea of the passage is Thanks to interventions, the dust storms of the Filthy Fifties were less severe than those of the Dirty Thirties. How does the detail in bold develop the main idea?
The southern Great Plains, an area of the U.S. known for its wheat production, was struck by a severe drought in the early 1930s. Farmers were unable to coax wheat from the parched earth. Huge swaths of plowed land, unanchored by native grasses, were left exposed to the region's strong winds, resulting in years of dust storms that earned the decade the title the Dirty Thirties. Facing poverty and dust inhalation, four hundred thousand people fled the region. Years later, a resurgence of dust storms occurred during another drought. However, the extent of the damage during the Filthy Fifties (as the decade came to be called) offered a contrast to the Dirty Thirties. Not only was the drought shorter, but the land was less vulnerable. In the intervening years, the federal government had restored prairie grasses, while farmers had also applied techniques to prevent soil erosion.