Climate curve and sea level curve covering the past 540 million years. The shaded area represents … More data variation.
JUDD et al. 2024/Science, VAN DER MEER et al. 2025/Earth and Planetary Science Letters
Two new studies offer the most detailed glimpse yet of how Earth’s climate and sea levels have changed during the Phanerozoic — the latest geologic eon covering the time period from 538.8 million years ago to the present.
The first curve reveals that Earth’s temperature has varied more than previously thought over much of the Phanerozoic eon and also confirms that Earth’s temperature is strongly correlated to carbon-dioxide levels in the atmosphere.
The scientific team from Arizona compiled more than 150,000 published data points, their colleagues at the University of Bristol generated more than 850 simulations of what Earth’s climate could have looked like at different periods. Using special data assimilation protocols, the different datasets were combined to create an accurate curve of how Earth’s global temperature has varied over the past 485 million years.
The climate curve starts in the Hirnantian, a period of major climatic oscillation lasting from approximately 460 to around 420 million years. The coldest period in the analyzed timescale is the Karoo glaciation, lasting from approximately 360 to 260 million years. But overall, the Phanerozoic was characterized by mild to warm climates, with global mean surface temperatures spanning from 11 to 36 degrees Celsius. In the warmest periods global temperatures did not drop below 25 degrees Celsius. In the last 60 million years, after a peak during the “Cretaceous Hothouse,” Earth started to cool down. The global average temperature today is about 15 degrees Celsius. The authors also note that the periods of extreme heat were most often linked to elevated levels of the greenhouse gas carbon-dioxide in the atmosphere.
The second curve shows how sea levels correlate both with tectonic activity — closing or opening oceanic basins and shifting continents — and how much water is trapped in ice caps and glaciers.
“Plate tectonics determines the depth of the oceans. If the ‘bathtub’ becomes shallower, then the water level will rise. Ice caps on continents withhold water from the ocean, but when the ice melts, the ‘bath water level’ will rise, ” explains study lead author Dr. Douwe van der Meer, guest researcher at Utrecht University.
To assess sea level changes, the scientists looked at the prevailing sediment type deposited at the time. Claystone typically forms in deeper marine settings, while sandstone is deposited in shallow basins. This preliminary curve was then combined with data derived from fossils of organisms living in a warm or cool environments, simulations of orbital parameters and paleogeographic models, visualizing the distribution of land and sea during different geological periods.
With this data, the authors were able to estimate the position of the continents in relation to the poles and the prevailing climate, reconstructing the volume of continental ice caps.
Sea levels were relatively low during the first 400 million years, reflecting the cooler climate and low tectonic activity. During the Carboniferous (358-298 million years ago) there were very large sea level variations due to a large ice cap covering the landmass of Gondwana in the southern hemisphere.
During the Cretaceous (145-66 million years ago) the supercontinent of Pangaea started to break up, and the hothouse climate caused the poles to be free of ice and snow. These two effects resulted in global sea levels being more than 200 meters higher than they are at present.
Over the next 60 million years, Earth has cooled, and approximately 30 million years ago the first ice sheets began to form at the poles. The past 2 million years were characterized by a series of ice-ages, when large parts of North America and Europe were covered by ice, and sea levels dropped up to 100 meters.
Climate and paleogeographic models not only help map Earth’s past more accurately, they can also enhance models used to simulate how sea levels will rise as the Earth is warming — thanks to our greenhouse gas emissions. “High or low sea levels, it’s all happened before in the geological past,” Van der Meer concludes.
The climate study, “A 485-million-year history of Earth’s surface temperature,” was published in the journal Science and can be found online here.
Additional material and interviews provided by the Smithsonian Institution and University of Arizona.
The sea level study, “Phanerozoic orbital-scale glacio-eustatic variability,” was published in the journal Earth and Planetary Science Letters and can be found online here.
Additional material and interviews provided by University of Utrecht.