The Last Glacial Maximum (LGM) refers to that period in earth's history when the glaciers were at their thickest and the sea levels at their lowest. During the LGM, continent-wide ice sheets covered high latitude Europe and North America, and sea levels were between 120 and 135 meters lower than they are today. The evidence of this is seen in sediments laid down by sea level changes all over the world.
The ice volume approached their maximum values 30,000 calendar years ago. The lead up to the LGM was dramatic, with sea levels dropping 50 meters in about 1,000 years (that's about 2.5 inches a year). Those levels remained constant or nearly so until 19,000 years ago. After that period, the sea level rose about 15 mm per year until 9000 years ago. Modern sea levels were reached approximately 7,000 years ago.
One exception to the constant rise in sea level appears to have been during the Younger Dryas, a cooler, dryer period lasting between about 12,500 to 11,500 calendar years ago. Some evidence of glacier growth during the Younger Dryas has been identified in mountain ranges such as the Andes of South America.
Clark, Peter U. and Alan C. Mix 2002 Ice sheets and sea level of the Last Glacial Maximum. Quaternary Science Reviews 21(1-3):1-7.
Lambeck, Kurt, Yusuke Yokoyama, and Tony Purcell 2002 Into and out of the Last Glacial Maximum: sea-level change during Oxygen Isotope Stages 3 and 2. Quaternary Science Reviews 21(1-3):343-360.
This glossary entry is part of the Dictionary of Archaeology.