Complex sentence: Most woolly mammoth populations disappeared during the late Pleistocene and early Holocene, alongside most of the Pleistocene megafauna (including the Columbian mammoth), as part of the Quaternary extinction event, which began 40,000 years ago, and peaked between 14,000 and 11,500 years ago.
Split into simpler sentences: Most woolly mammoth populations disappeared during the late Pleistocene and early Holocene, alongside most of the Pleistocene megafauna (including the Columbian mammoth). This extinction formed part of the Quaternary extinction event, which began 40,000 years ago and peaked between 14,000 and 11,500 years ago.