Most life was wiped out, and the creatures that did survive huddled in small pockets of open water, where hot springs continued to bubble up. This was Snowball Earth â a deep freeze that began around 715 million years ago and held Earth in its icy grip for a good 120 million years. There are no other comparable glacial periods on Earth.
Lake Barkley Lake Levels. The lake's level is fluctuated from summer to winter for flood control purposes. Summer pool (359 ft. sea level) is normally reached by May 1. The water level begins dropping gradually on July 1, and winter pool (354 ft.) is reached by December 1.
That is twice the amount stored in Lake Mead, the largest reservoir in the U.S., which can hold two years' worth of Colorado River runoff. As Jay Famiglietti, a NASA scientist and study co-author wrote here, groundwater made up 75 percent of the water lost in the basin.