According to the Utah Geological Survey, the first ice age occurred over 2 billion years ago. Ice ages are long periods of time when global temperatures are cold and many areas of the Earth are covered by continental ice sheets and alpine glaciers.
Ice ages can last tens of millions of years. There have been at least five major ice ages in the history of the Earth. Many factors can cause an ice age, including changes in atmospheric and ocean circulation, varying concentrations of atmospheric carbon dioxide or even volcanic eruptions. The 21st century Earth is currently in an ice age that began approximately 3 million years ago and peaked about 20,000 years ago.