A groundbreaking study published in *Nature* has uncovered vital information about the evolution of eukaryotes, the complex life forms that include animals and plants. Researchers analyzed drill cores of 1.7 billion-year-old mudstone from the Northern Territory of Australia, identifying over 12,000 microscopic fossils of ancient eukaryotic organisms. These fossils were found exclusively in environments with oxygen, suggesting that even the earliest eukaryotes relied on oxygen for survival, contrary to previous beliefs that some could thrive without it. The findings indicate that these organisms lived in diverse habitats, from coastal mudflats to open seas, during a time when oxygen levels were likely much lower than today. This research not only sheds light on the conditions under which early eukaryotes evolved but also raises questions about the role of oxygen in their development. The study highlights the importance of fossil records in understanding the ancestry of complex life and offers a glimpse into the evolutionary processes that shaped our planet. Ongoing investigations into these ancient microfossils promise to deepen our understanding of life's origins.