When Did the Ice Ages Begin?

Earth has cycled through multiple glacial eras throughout its history. The earliest known glaciation occurred about 2.9 billion years ago (the Pongola). The most extreme were the Cryogenian "Snowball Earth" events (approximately 720-635 million years ago), when ice may have extended to the equator. The current Quaternary glaciation began about 2.58 million years ago, driven by the closure of the Isthmus of Panama (altering ocean currents), declining atmospheric CO2, and the Milankovitch cycles — periodic variations in Earth orbital eccentricity, axial tilt, and precession. Within this era, glacial periods (ice ages) lasting about 100,000 years alternate with warmer interglacial periods lasting 10,000-30,000 years. We currently live in the Holocene interglacial, which began about 11,700 years ago. At the Last Glacial Maximum (about 26,500 years ago), ice sheets up to 3 km thick covered much of North America and Europe.