Day length has increased dramatically over Earth’s history. More than three billion years ago, entire days may have been just six hours long. And around 2.4 to 2.2 billion years ago, geological records indicate that the amount of oxygen in the atmosphere shot up while the volume of carbon dioxide shrank. That rapid increase in oxygen is generally credited to the proliferation of marine cyanobacteria, some of which absorb energy from sunlight and produce oxygen.

Changes in day length and the rise of atmospheric oxygen have each been explored scientifically for decades, but no one thought to consider them together—until now.

Klatt, a microbiologist at the Max Planck Institute for Marine Microbiology in Germany, and her collaborators at the University of Michigan