Global warming. Rising sea levels. Massive volcanic activity around the world. Widespread erosion.

No, it’s not a scene from the latest Hollywood disaster film, The Day After Tomorrow, but the Earth as it appeared during the mid- to late-Cretaceous period when the largest dinosaurs ruled the planet, some 135 million to 65 million years ago.

Scientists have long sought clues to the Earth’s ancient climate from ice cores that go back hundreds of thousands of years. Now, UCSD chemists report that they have extended their glimpse of the Earth’s oceanic and atmospheric past to 130 million years, during one of its greatest upheavals of climatic change.

Their results, published in the June 11 issue of Science, provide a portrait of the interactions between the Earth and its atmosphere during the Cretaceous. That portrait should help scientists improve their predictions of how our climate might change as the accumulation of carbon dioxide and other greenhouse gases warm the planet.

“The planet during the Cretaceous was very different than it is today,” says Adina Paytan, an assistant professor of geological and environmental sciences at Stanford who began the study as a graduate student and postdoctoral fellow at UCSD. “The climate was extremely warm and global sea levels were significantly higher than they are today. Understanding how the atmosphere, land and ocean system interacted while in this global greenhouse mode is very relevant if we want to understand the fate of our future climate.”

“This was a time when there were no glaciers in either the Arctic or Antarctic,” says Miriam Kastner, a professor of earth sciences at UCSD’s Scripps Institution of Oceanography and a co-principal investigator of the study. “So the record that we have obtained is an unusual portrait of an extreme climate in the Earth’s past that will help us develop better predictive models in the future.”

“If we can explain the major excursions that occurred 100 million years ago, we can develop good models of what is going to happen in the future,” says Mark H. Thiemens, dean of UCSD’s Division of Physical Sciences and a co-author of the paper. “This was a period of extremes.”

The scientists obtained their high- resolution record of climatic changes during the Cretaceous from sulfur deposited over millions of years in ocean sediments. Sulfur in its various chemical forms can provide an uninterrupted record of large scale geochemical processes on the Earth’s land masses and its oceans, as well as an indirect measure of its atmosphere. Paytan, Kastner, Thiemens and Douglas Campbell, an undergraduate working in Kastner’s laboratory, found from their sulfur record that the Earth’s atmosphere went through sharp fluctuations in the amount of available oxygen during the Cretaceous. Whether the same will be true as we warm up our planet is anyone’s guess at this point.

“ One thing that we can learn from this record is that there might have been more rapid changes in the atmosphere of the Cretaceous than we knew about,” says Paytan. “Some relatively rapid changes can happen on Earth. So we have to be prepared.”