Lowest ERA in 1st Season

Lowest ERA, 20+ IP (1st Season, Since 1900)
0.00 Harry Coveleski (1907, Phillies)
0.38 Joba Chamberlain (2007, Yankees)
0.38 Buck O'Brien (1911, Red Sox)
0.39 Cliff Markle (1915, Yankees)
0.40 Joel Johnston (1991, Royals)
0.44 Craig Kimbrel (2010, Braves)
0.66 George McQuillan (1907, Phillies)
0.67 Kenley Jansen (2010, Dodgers)