This study of limestone has been conducted by American and Italian researchers and indicates that almost 183 million years ago, sea creatures became extinct due to a lack of oxygen in the oceans.

Research conducted by PNAS (Proceedings of the National Academy of Sciences) warns of the dangerous effects of oxygen depletion and climate change on oceans.

Read More: A girl was rescued 36 hours after being swept into sea

Many marine reptiles flourished during the Jurassic period, but due to volcanic activities in South Africa, almost 20,500 gigatons of carbon dioxide were released, causing a massive decline in oxygen in the oceans. As a result, all the sea creatures became extinct.

Limestone absorbs the chemicals that are produced through volcanic eruptions. By studying limestone sediments, researchers found that there was a massive change in the level of oxygen in oceans during ancient times, and researchers found that the oxygen level decreased to 8%, which covered more than three times the area of the United States.