TALLAHASSEE, Florida, Nov. 5 -- Florida State University issued the following news: By Kendall Cooper If Earth's history were a calendar year, humans would not appear until the last few minutes before midnight on Dec. 31. During the Proterozoic Eon -- 2.5 billion years to 543 million years ago -- the sun was still a young star, much dimmer than today, and Earth required a stronger greenhouse effect to compensate and maintain habitable temperatures for the planet's earliest lifeforms. New rese  more