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.
3. Hoover Dam created Americaâs largest reservoir. Formed by the damning of the Colorado River, Lake Mead, the nationâs largest reservoir, covers about 248 square miles and is capable of holding some 28.9 million acre-feet of water (an acre-foot is equivalent to about 325,000 gallons).