You've heard of global warming - How about global freezing?

Iceball Earth [17 Feb 2000] "For the primitive organisms unlucky enough to be around 2.4 billion years ago, the first global freeze was a real wipeout, likely the worst in the history of life on Earth. Few of the organisms escaped extinction, and those that did were forced into an evolutionary bottleneck that altered the diversity of life for eons."

Snowball Earth episode 2.4 billion years ago was hard on life, but good for modern industrial economy, research show, press release, Cal Tech

Paleoproterozoic snowball Earth: Extreme climatic and geochemical global change and its biological consequences, Proceedings of the National Academy of Science [Abstract - subscription fee required for full access]

Snowball Earth, Scientific American, January 2000

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