When was the first modern explanation of glacial ages proposed?

Ideas about past ice ages developed gradually, but major modern explanations emerged in the 19th century. Louis Agassiz proposed in the 1830s and 1840s that large parts of Europe and North America had once been covered by vast ice sheets. His work helped establish glaciology as a science and explained landforms such as moraines, erratics, and U-shaped valleys. The concept of ice ages became a central part of Earth science.