The air we breathe is twenty-one percent oxygen, an amount higher than on any other known world. While we may take our air for granted, Earth was not always an oxygenated planet. How did it become this way? This book is the most current account of the history of atmospheric oxygen on Earth.

What is it about planet Earth? -- Life before oxygen -- Evolution of oxygenic photosynthesis -- Cyanobacteria: the great liberators -- What controls atmospheric oxygen concentrations? -- The early history of atmospheric oxygen: biological evidence -- The early history of atmospheric oxygen: geological evidence -- The great oxidation -- Earth's Middle Ages: what came after the GOE -- Neoproterozoic oxygen and the rise of animals -- Phanerozoic oxygen -- Epilogue.