Glacial periods, also known as ice ages, are times in Earth's history when large areas of the planet were covered by ice sheets and glaciers. These periods are characterized by significantly lower global temperatures, which can last for thousands to millions of years. During glacial periods, sea levels drop as water is trapped in ice, affecting ecosystems and habitats. The most recent glacial period, known as the Quaternary glaciation, began around 2.58 million years ago and continues today, with alternating glacial and interglacial phases. The last major glacial advance occurred about 20,000 years ago, during the Last Glacial Maximum, when ice sheets extended over much of North America and Europe.