Coastal waters were an oxygen oasis 2.3 billion years ago
Despite being ripe for complex life, it took another 1.5 billion years for oxygen-hungry animals to evolve
![fossil eukaryote](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2017/01/011317_ts_oxygen-oasis_feat.jpg?fit=860%2C460&ssl=1)
OXYGEN OASIS Oxygen was abundant enough for complex life-forms such as this 1.4-billion-year-old fossilized eukaryote to thrive around 2.3 billion years ago, new research suggests. The expansion and diversification of eukaryotes nevertheless only came hundreds of millions of years later.
Andrew Knoll/Harvard University