Back on June 26, 2025 – Science News Desk, A new scientific report is sending a strong message: what happened hundreds of millions of years ago could be happening again but much faster this time.
In a study published on June 23, 2025, in the Proceedings of the National Academy of Sciences, researchers found that Earth went through at least five major carbon dioxide spikes between 310 and 290 million years ago. These events released huge amounts of CO₂ into the atmosphere and led to serious drops in ocean oxygen, harming sea life for thousands of years.
The researchers, led by Professor Isabel Montañez from the University of California, Davis, studied rock samples from deep in the ground in South China. These samples, taken from what was once the ocean floor, helped scientists trace how CO₂ levels and ocean oxygen changed over time.
One of the worst events happened about 304 million years ago. Back then, volcanoes and underground coal fires poured CO₂ into the air. As the planet heated up, the oceans warmed too. Warmer water holds less oxygen, and fresh water from melting ice made it harder for oxygen to reach deeper parts of the sea. The result? Nearly one-quarter of the ocean floor lost all its oxygen — creating large "dead zones" where few sea creatures could survive.
What’s especially worrying, scientists say, is that Earth had more oxygen in the air back then — up to 50% more than today. Even with all that extra oxygen, the rise in CO₂ still caused the oceans to lose oxygen. That’s important because today, human activity is causing CO₂ levels to rise far more quickly than those ancient events.
Since the 1950s, the world’s oceans have already lost about 2% of their oxygen. If greenhouse gases keep rising at the current pace, experts expect that number could grow by another 3–4% by the end of this century. That could lead to more dead zones in the ocean, putting fish and other marine life at risk.
The study also found that these past oxygen drops slowed down evolution in the oceans. Species disappeared or stopped changing for long periods. While these events didn’t cause the biggest mass extinctions in Earth’s history, they still caused serious stress to underwater ecosystems.
Dr. Montañez says these ancient examples are the best natural evidence we have for what might happen now. The warning is clear: big jumps in carbon dioxide, even in a world with more oxygen, can still drain the oceans and hurt life below the surface.
Today, we’re seeing similar effects unfold — only much faster. The planet may be heading toward a new version of an old crisis, unless action is taken soon to reduce emissions and protect ocean health.
