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.
1 Huronian-The Huronian ice age was one of the longest ice ages in the Earth's history. 2  It lasted from about 2400 to 2100 million years ago. 3  Scientists think it may have been caused by a lack of volcanic activity lowering the carbon dioxide in the atmosphere.