<human>:  When was the Last Glacial Maximum?
<bot>: The Last Glacial Maximum was the coldest period of the last glacial period. It started around 21,000 years ago and ended around 12,000 years ago. The Last Glacial Maximum was a period of time when the Earth was covered in ice. The ice sheets covered most of North America, Europe, and Asia. The ice sheets were so thick that they blocked the sun from reaching the Earth, causing the Earth to cool.