Glacial Theory

Glacial theory is the recognition that large parts of the Earth's surface were once covered by extensive ice sheets and glaciers during past ice ages, and that many landscape features once attributed to other causes, particularly a great flood, are instead the direct physical result of past glacial activity such as scouring, deposition and the transport of large boulders far from their origin. Swiss-born naturalist Louis Agassiz developed and forcefully championed the theory beginning with an 1837 address to the Swiss Society of Natural Sciences, building on earlier, less widely accepted observations by other naturalists, and he spent much of the following decade traveling to gather further supporting field evidence across Europe. Agassiz's theory faced considerable initial resistance from the scientific establishment of his time, since the prevailing explanation for the same landscape evidence had been a single catastrophic flood, but the glacial explanation steadily gained acceptance through the mid-nineteenth century as further field evidence accumulated. Glacial theory became foundational to the modern scientific understanding of ice ages and Earth's long-term climate history, establishing that the planet's climate has swung repeatedly between warmer and much colder states over geological time.