The story
The Cretaceous Thermal Maximum, centered on the Turonian stage about 94 to 90 million years ago, was the hottest stretch of the last 100 million years. Oxygen isotopes in fossil shells show that tropical sea surface temperatures reached around 33 to 37 C. There were no permanent ice sheets, sea level stood well over 100 m above today's, and crocodile relatives and champsosaurs lived in the Canadian Arctic, while forests grew in Antarctica.
The heat followed a surge in volcanic activity, including large igneous provinces in the Caribbean, which pushed carbon dioxide levels far above modern ones. Just before the peak, around 94 million years ago, Oceanic Anoxic Event 2 left black, oxygen-poor mud on the seabed worldwide and killed many marine species. Afterward the climate cooled slowly through the rest of the Cretaceous. The warm, flooded world helped create the shallow seas, such as the Western Interior Seaway, that mosasaurs and plesiosaurs ruled.
Why it mattered
- The warm world offers a case study of what very high carbon dioxide can do to ocean chemistry and sea level.
- The flooding of continents produced large shallow seas and the chalk and black shales we use as oil source rocks.
- It helped shape the habitats of mosasaurs, plesiosaurs and the late Cretaceous dinosaurs.
Sources
- Cretaceous Thermal Maximum (Norris lab) Scripps Institution of Oceanography
- Evidence for extreme climatic warmth from Late Cretaceous Arctic vertebrates Science (PubMed)
- Development of the Cretaceous Greenhouse Climate and the Oceanic Thermal Structure Paleontological Research
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