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A new study co-led by the Smithsonian and the University of Arizona offers the most detailed glimpse yet of how Earth's surface temperature has changed over the past 485 million years.

In a paper published Sept. 19, in the journal Science, a team of researchers, including paleobiologists Scott Wing and Brian Huber from the Smithsonian's National Museum of Natural History, produce a curve of global mean surface temperature (GMST) across deep time—the Earth's ancient past stretching over many millions of years.

The new curve reveals that Earth's temperature has varied more than previously thought over much of the Phanerozoic Eon, the past 540 million years of geologic time when life has diversified, populated land and endured multiple mass extinctions. The curve also confirms that Earth's temperature is strongly correlated to the amount of carbon dioxide in the atmosphere.

The team created the temperature curve utilizing an approach called data assimilation. This allowed the researchers to combine data from the geologic record and climate models to create a more cohesive understanding of ancient climates.

"This method was originally developed for weather forecasting," said Emily Judd, the lead author of the new paper and a former postdoctoral researcher at the National Museum of Natural History and the University of Arizona. "Instead of using it to forecast future weather, here we're using it to hindcast ancient climates."

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