Scientists have long debated a critical question: did life learn to breathe oxygen before or after the Great Oxidation Event about 2.4 billion years ago, when atmospheric oxygen first began to accumulate? A new CUHK study now provides strong evidence that it happened much earlier, hundreds of millions of years before the event. Using an AI model, CUHK researchers found that long before oxygen began accumulating in Earth's atmosphere, tiny microbial pioneers were already experimenting with breathing it, thriving inside microscopic oxygen-rich pockets. This discovery not only rewrites the history of life on Earth but also has profound implications in an era of climate change.