Geologists therefore hypothesize that the world at that time was affected by a very severe glaciation , perhaps the most severe in geologic history ( see Snowball Earth ) .
Similar deposits are found over North America during the same period , some 700 to 800 mya .
Geologists hypothesize that the world at that time was affected by a very severe glaciation , perhaps the most severe in geologic history ( see Snowball Earth ) .
Similar deposits are found over North America during the same period , some 700 to 800 mya .