An international team of scientists has found that changes in Earth’s orbit favoring warmer conditions may have helped trigger a rapid global warming event 56 million years ago known as the Paleocene-Eocene Thermal Maximum (PETM).
An international team of scientists suggests that changes in the Earth’s orbit that have resulted in warmer conditions may have played a role in the current rapid global warming event that occurred 56 million years ago. This event, known as the Late Thermal Maximum (PETM-Eocene-Eocene), is considered to be the analogue of today’s climate change.
“The Palaeocene-Eocene Thermal is the closest thing we have in the geologic record to anything like what we’re experiencing now and what we’re experiencing in the future with climate change,” said Lee Kump, a professor of geoscience at Penn State University. “There is a lot of interest in better analyzing that history, and our work addresses the big questions about burning events and carbon emissions.”
A team of scientists cored samples from the well-preserved PETM record near Maryland using an astrochronological method of dating sedimentary orbital layers that occur over many periods of time called Milankovitch cycles.
Victoria Fortiz (right), then a student at Penn State, and Jean Self-Trail, a research geologist with the US Geological Survey, work on a core sample from a site in Maryland’s Howard Tract. Credit: Penn State
They found that the shape of the Earth’s orbit, or the eccentricity and wobble in its rotation or precession, favored hotter conditions during the PETM attack and that these orbital shapes simultaneously played a role in triggering the event.
“Orbital slip can be attributed to the emission of carbon that caused several degrees of global warming in the PETM as opposed to what is a more popular interpretation that the moment when massive volcanism released the carbon and caused the bear event,” said Kump, John Leone. Dean in the College of Earth and Mineral Sciences.
The findings were published in a journal
“Those rates are close to an order of magnitude slower than the rate of carbon emissions today, so that is cause for some concern,” Kump said. “We are now emitting carbon at a rate that’s 5 to 10 times higher than our estimates of emissions during this geological event that left an indelible imprint on the planet 56 million years ago.”
The scientists conducted a time series analysis of calcium content and magnetic susceptibility found in the cores, which are proxies for changes in orbital cycles, and used that information to estimate the pacing of the PETM.
Earth’s orbit varies in predictable, calculable ways due to gravitational interactions with the sun and other planets in the solar system. These changes impact how much sunlight reaches Earth and its geographic distribution and therefore influence the climate.
“The reason there’s an expression in the geologic record of these orbital changes is because they affect climate,” Kump said. “And that affects how productive marine and terrestrial organisms are, how much rainfall there is, how much erosion there is on the continents, and therefore how much sediment is carried into the ocean environment.”
Erosion from the paleo Potomac and Susquehanna rivers, which at the onset of the PETM may have rivaled the discharge of the Amazon River, carried sediments to the ocean where they were deposited on the continental shelf. This formation, called the Marlboro Clay, is now inland and offers one of the best-preserved examples of the PETM.
“We can develop histories by coring down through the layers of sediment and extracting specific cycles that are creating this story, just like you could extract each note from a song,” Kump said. “Of course, some of the records are distorted and there are gaps — but we can use the same types of statistical methods that are used in apps that can determine what song you are trying to sing. You can sing a song and if you forget half the words and skip a chorus, it will still be able to determine the song, and we can use that same approach to reconstruct these records.”
Reference: “Astrochronology of the Paleocene-Eocene Thermal Maximum on the Atlantic Coastal Plain” by Mingsong Li, Timothy J. Bralower, Lee R. Kump, Jean M. Self-Trail, James C. Zachos, William D. Rush and Marci M. Robinson, 24 September 2022, Nature Communications.
DOI: 10.1038/s41467-022-33390-x
The study was funded by the National Key R&D Program of China and the Heising-Simons Foundation.
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