In 1742, Pierre Martel (1706–1767), an engineer and geographer living in Geneva, visited the valley of Chamonix in the Alps of Savoy. Two years later he published an account of his journey. He reported that the inhabitants of that

There have been at least five major ice ages in Earth's history (the Huronian, Cryogenian, Andean-Saharan, late Paleozoic, and the latest Quaternary Ice Age). Outside these ages, Earth seems to have been ice-free even in high latitudes; such periods are known as

Each glacial period is subject to positive feedback which makes it more severe, and negative feedback which mitigates and (in all cases so far) eventually ends it.
Positive
An important form of feedback is provided by Earth's

The current geological period, the Quaternary, which began about 2.6 million years ago and extends into the present, is marked by warm and cold

There are three main types of evidence for ice ages: geological, chemical, and paleontological.
Geological evidence for

Within the current glaciation, more temperate and more severe periods have occurred. The colder periods are called glacial periods, the

The causes of ice ages are not fully understood for either the large-scale ice age periods or the smaller ebb and flow of glacial–interglacial