Earth Sciences professor Matthew Saltzman is co-author on a paper in Science this month, which links biological evolutionary innovations to a dramatic rise of atmospheric oxygen in the Devonian period ~400 million years ago, and a subsequent step-change to relatively sustainable near-modern conditions at ~200 Ma near the start of the Jurassic. The study integrated geologic proxy data from iodine to calcium ratios in ancient carbonate sediments with quantitative modeling of Earth’s oxygen levels. The iodine proxy is novel in that it can monitor upper ocean oxygen levels around threshold levels for metazoan survival. You can view the full study in Science Geoscience here and a related media story here.