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.
Ice Ages: Timeline. Past 1,000,000 years. Past 150,000 years. Using chemical information collected from ice cores and from shells of organisms preserved in deep-sea sediments, geologists have been able to map out how Earth's climate has changed over time. Climate swings between cold periods, called glacials, and warm periods, called interglacials.