How rising ocean oxygen 390 million years ago reshaped evolution

A recent study published in the Proceedings of the National Academy of Sciences reveals that a permanent rise in deep-ocean oxygen levels during the Middle Devonian period (approximately 393–382 million years ago) played a pivotal role in reshaping marine life and evolution. This oxygen increase enabled jawed fishes (gnathostomes) and other animals to colonize deeper ocean habitats along the outer continental shelves, coinciding with a major burst of biodiversity known as the mid-Paleozoic marine revolution. The research suggests that oxygen was not merely a necessary factor but a key driver dictating when and where early vertebrates could thrive, with the initial Cambrian oxygen pulse around 540 million years ago being short-lived and insufficient for sustained diversification in deep waters. The study also highlights a connection between terrestrial and marine ecosystems, noting that the spread of woody plants on land—early precursors to forests—contributed to increased atmospheric oxygen, which in turn elevated oxygen levels in the deep ocean. This terrestrial innovation likely