The ground freezes when its temperature reaches zero degrees Celsius, or 32 degrees Fahrenheit. Commonly, the ground is considered frozen when all the moisture in between the rocks, soil and sediment freezes. The freezing of moisture is only an indicator, however, and frozen ground is ultimately determined by temperature alone.
Frozen ground can be found all over the Earth and can be seasonally frozen ground or permafrost. Seasonally frozen ground is soil that freezes in winter and melts in the summer. Most of the land above the Equator is seasonally frozen ground. Permafrost is ground that stays below freezing for 2 years or more and is mostly found in Alaska and northern part of Canada.