PALEOCLIMATOLOGY
Dinosaur climate probed Ancient lake sediments in China record epic temperature swings, biotic turnover before the mass extinction By Jane Qiu, in Beijing
PHOTO: COURTESY OF ICDP
W
ell before an asteroid struck the planet some 66 million years ago, Earth was already in turmoil, a record from an ancient lakebed in northeastern China suggests. Investigators knew from ocean floor sediments that the climate was unstable at the end of the Cretaceous period, when the dinosaurs were making their last stand. But findings from deep drilling in the Songliao Basin, presented at a conference here this spring, show that the climate swings on land were far more drastic, with average annual temperatures going up or down by as much as 20°C over tens of thousands of years—a geological eyeblink. “It certainly wasn’t a good time for the dinosaurs,” says Robert Spicer, a paleoclimatologist at the Open University in Milton Keynes, U.K. The findings support a growing consensus that a one-two punch felled the dinosaurs and their contemporaries. Extreme climate fluctuations and tectonic processes that eliminated seaways during the last few million years of the Cretaceous snuffed out some species and hobbled others, the theory holds, before the massive asteroid slammed into the Yucatán Peninsula and finished off about three-quarters of Earth’s life forms. The direst picture yet of the Cretaceous’s waning days comes from the Songliao Basin. Covering 260,000 square kilometers,
much of the New Zealand–sized swath was a gigantic lake for 80 million years during the Cretaceous. The lakebed’s sediments “provide a unique record of what the land environment was like during this turbulent time,” says Page Chamberlain, a paleoclimatologist at Stanford University in Palo Alto, California, and a principal investigator of the Songliao International Continental Scientific Drilling Project. Over the past decade, the drilling team, led by geologist Wang Chengshan of the China University of Geosciences in Beijing, has delved 2.6 kilometers into the basin, below the K-Pg boundary between the Cretaceous and the Paleogene periods. By analyzing oxygen and carbon isotope ratios in the sediment cores, they could trace the seesawing temperatures during the last 6 million years of the Cretaceous, an age known as the Maastrichtian. Songliao’s high latitude likely amplified the fluctuations recorded in the marine records, which tend to blend and blur climate signals. And because the lake sediments accumulated about 10 times faster than the marine sediments did, they offer a finer grained and more precisely dateable picture. But the main selling point of Songliao is the unparalleled continuous record of how the Cretaceous played out on land, says Stephan Graham, a sedimentary geologist at Stanford University, who is also a principal investigator of the project.
SCIENCE sciencemag.org
The sediments reveal not only the extent of the temperature swings, but also a likely cause. Two major Maastrichtian warming events captured in the Songliao cores— 68 million years ago and 66.3 million years ago—coincide with massive eruptions of the Deccan Traps, a volcanic region in presentday India. According to carbon isotope studies, that second warming event was marked by a rapid doubling in atmospheric carbon dioxide. “This was the time when the bulk of Deccan eruptions occurred, which presumably released a massive amount of carbon dioxide,” says Zhang Laiming of the China University of Geosciences. The intense greenhouse effect drove average temperatures to about 22.3°C— compared with 5°C at Songliao today. Adding to the climate turmoil, the warming was interrupted just after the K-Pg boundary by a brief cooling episode, which the team attributes to dust, soot, and aerosols from the Yucatán impact. As the Maastrichtian climate convulsed, ecosystems changed. The Songliao sediments trapped spores, pollen, algae, and ostracods, or seed shrimp. To the researchers’ surprise, some of the species typical of the Paleocene—the geological epoch following the Cretaceous—emerged several million years before the K-Pg boundary. Turnovers in the biota, Wang says, “had already been under way when the asteroid struck.” Paleontologists suspect that dinosaurs were feeling the stress. In a review last August in The Geological Society of America Special Papers, paleontologist David Archibald of San Diego State University and colleagues noted that the number of nonavian dinosaur species shrank by half in the last 10 million years of the Cretaceous, with the biggest losses occurring in the Maastrichtian. The Chicxulub impact was, Wang says, “the straw that broke the camel’s back.” Put another way, Spicer says, “if the asteroid came in on a less stressed system, the effects would not have been so severe.” Having conquered the K-Pg boundary at Songliao, Wang is pressing deeper into the basin—all the way to the Jurassic-Cretaceous boundary about 145 million years ago, a time also marked by climatic havoc, mass extinctions, and species turnovers. Those cores, from as much as 6.4 kilometers below the surface, will span the entire Cretaceous period and, Spicer says, give fresh insights into the world in which the dinosaurs thrived and ultimately died. “You have to look at the bigger picture to fully understand what happened at the boundaries.” ■ 12 JUNE 2015 • VOL 348 ISSUE 6240
Published by AAAS
1185
Downloaded from www.sciencemag.org on June 12, 2015
A decadelong drilling project in northeastern China has penetrated sediments from as early as 100 million years ago.
Dinosaur climate probed Ancient lake sediments in China record epic temperature swings, biotic turnover before the mass extinction By Jane Qiu, in Beijing
PHOTO: COURTESY OF ICDP
W
ell before an asteroid struck the planet some 66 million years ago, Earth was already in turmoil, a record from an ancient lakebed in northeastern China suggests. Investigators knew from ocean floor sediments that the climate was unstable at the end of the Cretaceous period, when the dinosaurs were making their last stand. But findings from deep drilling in the Songliao Basin, presented at a conference here this spring, show that the climate swings on land were far more drastic, with average annual temperatures going up or down by as much as 20°C over tens of thousands of years—a geological eyeblink. “It certainly wasn’t a good time for the dinosaurs,” says Robert Spicer, a paleoclimatologist at the Open University in Milton Keynes, U.K. The findings support a growing consensus that a one-two punch felled the dinosaurs and their contemporaries. Extreme climate fluctuations and tectonic processes that eliminated seaways during the last few million years of the Cretaceous snuffed out some species and hobbled others, the theory holds, before the massive asteroid slammed into the Yucatán Peninsula and finished off about three-quarters of Earth’s life forms. The direst picture yet of the Cretaceous’s waning days comes from the Songliao Basin. Covering 260,000 square kilometers,
much of the New Zealand–sized swath was a gigantic lake for 80 million years during the Cretaceous. The lakebed’s sediments “provide a unique record of what the land environment was like during this turbulent time,” says Page Chamberlain, a paleoclimatologist at Stanford University in Palo Alto, California, and a principal investigator of the Songliao International Continental Scientific Drilling Project. Over the past decade, the drilling team, led by geologist Wang Chengshan of the China University of Geosciences in Beijing, has delved 2.6 kilometers into the basin, below the K-Pg boundary between the Cretaceous and the Paleogene periods. By analyzing oxygen and carbon isotope ratios in the sediment cores, they could trace the seesawing temperatures during the last 6 million years of the Cretaceous, an age known as the Maastrichtian. Songliao’s high latitude likely amplified the fluctuations recorded in the marine records, which tend to blend and blur climate signals. And because the lake sediments accumulated about 10 times faster than the marine sediments did, they offer a finer grained and more precisely dateable picture. But the main selling point of Songliao is the unparalleled continuous record of how the Cretaceous played out on land, says Stephan Graham, a sedimentary geologist at Stanford University, who is also a principal investigator of the project.
SCIENCE sciencemag.org
The sediments reveal not only the extent of the temperature swings, but also a likely cause. Two major Maastrichtian warming events captured in the Songliao cores— 68 million years ago and 66.3 million years ago—coincide with massive eruptions of the Deccan Traps, a volcanic region in presentday India. According to carbon isotope studies, that second warming event was marked by a rapid doubling in atmospheric carbon dioxide. “This was the time when the bulk of Deccan eruptions occurred, which presumably released a massive amount of carbon dioxide,” says Zhang Laiming of the China University of Geosciences. The intense greenhouse effect drove average temperatures to about 22.3°C— compared with 5°C at Songliao today. Adding to the climate turmoil, the warming was interrupted just after the K-Pg boundary by a brief cooling episode, which the team attributes to dust, soot, and aerosols from the Yucatán impact. As the Maastrichtian climate convulsed, ecosystems changed. The Songliao sediments trapped spores, pollen, algae, and ostracods, or seed shrimp. To the researchers’ surprise, some of the species typical of the Paleocene—the geological epoch following the Cretaceous—emerged several million years before the K-Pg boundary. Turnovers in the biota, Wang says, “had already been under way when the asteroid struck.” Paleontologists suspect that dinosaurs were feeling the stress. In a review last August in The Geological Society of America Special Papers, paleontologist David Archibald of San Diego State University and colleagues noted that the number of nonavian dinosaur species shrank by half in the last 10 million years of the Cretaceous, with the biggest losses occurring in the Maastrichtian. The Chicxulub impact was, Wang says, “the straw that broke the camel’s back.” Put another way, Spicer says, “if the asteroid came in on a less stressed system, the effects would not have been so severe.” Having conquered the K-Pg boundary at Songliao, Wang is pressing deeper into the basin—all the way to the Jurassic-Cretaceous boundary about 145 million years ago, a time also marked by climatic havoc, mass extinctions, and species turnovers. Those cores, from as much as 6.4 kilometers below the surface, will span the entire Cretaceous period and, Spicer says, give fresh insights into the world in which the dinosaurs thrived and ultimately died. “You have to look at the bigger picture to fully understand what happened at the boundaries.” ■ 12 JUNE 2015 • VOL 348 ISSUE 6240
Published by AAAS
1185
Downloaded from www.sciencemag.org on June 12, 2015
A decadelong drilling project in northeastern China has penetrated sediments from as early as 100 million years ago.
