The last ice age was about 125,000 years ago. 125,000 years ago, Earth was in an interglacial period similar to today's because glaciers were confined to high latitudes and high altitudes. However, over the past 125,000 years, the Earth system has gone through an entire glacial-interglacial cycle, and this is only the latest of many cycles that have occurred over the past million years. The most recent cooling and glacial period began about 120,000 years ago. Huge ice sheets formed and persisted over much of Canada and northern Eurasia. The earliest documented ice age, and possibly the most severe in the past billion years, occurred between 850 and 630 million years ago (the low temperature period), and may have produced a snowball Earth in which permanent ice covered The entire planet is affected by the accumulation of greenhouse gases such as carbon dioxide produced by volcanoes. "The presence of ice on continents and floating ice in oceans inhibits silicate weathering and photosynthesis, the two major sinks for carbon dioxide today." The reason for the outbreak of Ji Da, although this theory is new and controversial.