As early as the 18th century, some scattered boulders were found in many parts of Europe, which are completely different from the surrounding rocks. In the age of underdeveloped machinery, the origin of these rocks was quite suspicious. After decades of research and debate, scientists speculate that the climate has become very cold in the past period, so the scope of polar and continental ice sheets and mountain glaciers has expanded. These boulders may have been transported by glaciers or sea ice at that time. When the climate warms and the glaciers recede, these boulders remain. This is people's initial understanding of the ice age.
After nearly 300 years of in-depth research, scientists have basically confirmed through various methods that there have been many ice age events in the history of the earth, such as the Huron ice age 2.4-2.2 billion years ago, when most parts of the earth may be covered with ice and snow; During the Neoproterozoic ice age, 750 million to 630 million years ago, the ice sheet once pushed into the equatorial region, with an ice thickness of 1 km; During the Carboniferous Permian ice age, 350-270 million years ago, the polar ice sheet reached the center of Gondwana; From 2.6 million years ago to the present Quaternary ice age, most parts of North America and Europe were covered with ice up to 2 kilometers thick, resulting in a drop of 120 meters in sea level.
However, the earth did not always remain frozen and cold during these ice ages, which lasted for millions or even hundreds of millions of years. There will also be the replacement of cold warm climate. Take the recent Quaternary glacial period as an example, in which there are many cold glacial periods (also known as sub glacial period or glacial period) and warm interglacial periods, ranging from thousands of years to tens of thousands or hundreds of thousands of years. For example, the film "ice age" shows more scenes of the middle and last glacial period of the Quaternary ice age 110000 ~ 10000 years ago. Some scientists believe that the Quaternary ice age has not ended yet, and we are now in a relatively warm interglacial period in this ice age.