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.
There have been approximately 11 different ice ages that have occurred during the earthâs 4.6 billion years of existence. The last ice age was called âThe Great Ice Ageâ, and it occurred 11,000 years ago. During the âGreat Ice Ageâ over a third of the earth was covered in ice, and the air had less carbon dioxide in it.