Background color for WARNING safety signs, labels, and tags. Marking hazardous parts of machines with may cut, crush, or otherwise injure. Emphasizing hazards when enclosure doors are open or when gear, belt, or other guards around moving equipment are opened or removed, exposing unguarded hazards. Marking exposed edges of
Bibcode:1995GBioC...9..377C. doi:10.1029/95GB01107. An ice age is a period of long-term reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers.
How Many Ice Ages Were There? There have been at least five major ice ages in the Earthâs past. Outside these ages, the Earth seems to have been ice-free even in high latitudes. Rocks from the earliest well established ice age, called the Huronian, formed around 2.4 to 2.1 Ga (billion years) ago during the early Proterozoic Eon.