EARLY microbes may have filled the Earth’s atmosphere with oxygen, with a
little help from rocks in the mantle.
Photosynthetic microbes began generating oxygen at least 2.7 billion years
ago. But oddly, it wasn’t until 2.3 billion years ago that oxygen became a major
part of the atmosphere. Now Lee Kump of Pennsylvania State University suggests a
change in the Earth’s mantle made all the difference.
Kump points out that the planet formed with a mantle that released reducing
volcanic gases like hydrogen, which reacts with oxygen. So over time the mantle
became gradually oxidised, and oxidised rocks rose to…
