"Earth has experienced cold periods (informally referred to as “ice ages,” or "glacials") and warm periods (“interglacials”) on roughly 100,000-year cycles for

"Earth has experienced cold periods (informally referred to as “ice ages,” or "glacials") and warm periods (“interglacials”) on roughly 100,000-year cycles for at least the last 1 million years. The last of these ice age glaciations peaked* around 20,000 years ago." "The causes of ice ages are not fully understood for either the large-scale ice age periods or the smaller ebb and flow of glacial–interglacial periods within an ice age." https://www.climate.gov/news-features/climate-qa/whats-hottest-earths-ever-been https://www.climate.gov/news-features/climate-qa/whats-hotte...