Chapter 22, Problem 1RQ

To determine

The evidence offered by Louis Agassiz to support the idea of an ice age.

Answer to Problem 1RQ

The evidence offered by Louis Agassiz was the mysterious erratics of Europe that were left by enormous sheets of ice that had once covered much of the continent. He noticed that many European deposits consisted of boulders, which water could not carry and were unsorted (water produces sorted deposits because carrying capacity is a function of velocity).

Explanation of Solution

An ice age is a period in the Earth’s history in which the climate was extremely cold, resulting in the existence or expansion of continental ice sheets and mountain glaciers. There are two stages within an ice age, where periods of cold climate are termed as ‘glacial periods’ or ‘glaciations’, and alternative warm periods that are ‘interglacial’.

In 1837, Louis Agassiz, a Swiss geologist proposed that the Earth had been subject to a past ice age. He proposed that ancient glaciers not only flowed externally from the Alps but also on the plains and mountains of Europe. Agassiz found boulders protruding from the ground in locations that are not presently glaciated. He proposed that the boulders are erratics left by now-vanished glaciers.

“Glaciers are streams or sheets of recrystallized ice that flow gradually under the influence of gravity and last for an entire year”. He observed that the slow-moving masses of glaciers could carry massive boulders, as well as mud and sand because ice is a solid and had the power to support the weight of the rock.

He realized that unlike rivers, glaciers do not sort sediment as they flow and leave unsorted sediments later when they melt. Later in life, Agassiz traveled to the United States and identified many glacial features in North America's landscape, proving that the last ice age did not affect just Europe but vast areas of the Earth.