New Info from Ancient Rocks Upends Popular Theory

Roughly 2.5 to 2 billion years ago, the earth’s surface experienced the biggest chemical change in its history when oxygen became abundant in the atmosphere, eventually leading to the evolution of complex life forms such as plants and animals that emerged half a billion years ago. During this first rise of oxygen, large quantities of microbial biomass were buried on the seafloor and locked carbon into rocks with an anomalous isotopic signature. Many researchers think this signature is a sign of the carbon cycle thrown off balance across the whole planet.