The massive asteroid strike off Mexico's Yucatan Peninsula 66 million years ago wasn't the only reason why the dinosaurs became extinct. It was a combination of this explosion plus horrendous climate change that did in the dinosaurs and triggered the Cretaceous-Paleogene (K-Pg) extinction event.
This finding by a research team from the University of Florida and the University of Michigan argues there were two "kill mechanisms," and not one, which ignited the K-Pg extinction event.
The first was the asteroid strike while the other was climate change that caused ocean temperatures to rise some 14 degrees Fahrenheit before the asteroid strike. This warming was related to volcanic eruptions of the Deccan Traps in India. A "one-two punch" and not a single blow killed the dinosaurs.
Researchers utilized a new technique of analysis to reconstruct Antarctic Ocean temperatures. The results support the idea the combined impacts of volcanic eruptions and an asteroid strike triggered the K-Pg extinction event, one of the Earth's biggest mass extinctions in which three-quarters of the plant and animal species on Earth were obliterated.
The researchers used a recently developed technique called the "carbonate clumped isotope paleothermometer" to analyze the chemical composition of fossil shells in the Antarctic Ocean. Their analysis shows that ocean temperatures at the time had risen by some 14 degrees Fahrenheit.
To create their new temperature record spanning 3.5 million years at the end of the Cretaceous and the start of the Paleogene Period, researchers analyzed the isotopic composition of 29 quite well-preserved shells of clam-like bivalves collected on Seymour Island in the Antarctic.
The Cretaceous-Paleogene boundary is a physical boundary usually marked by a thin band of rock found in geological structures around the world. It's widely associated with the mass extinction that occurred 66 million years ago.
The K-Pg boundary contains iridium, also found in asteroids, meteorites and comets, bolstering the theory an asteroid killed most of the creatures of the Cretaceous Period.
"Now, years later, everyone is using this new tool called clumped isotope paleothermometery, which is a bit different than the traditional method," said University of Florida geochemist Andrea Dutton.
"This technique is only a function of temperature. Salinity has nothing to do with it. We're looking at the clumping of oxygen isotopes rather than the relative amount of oxygen isotopes in the shell, and this is helping us re-interpret the data."
The data show two significant temperature spikes. The first corresponds to the eruption of the Deccan Traps, one of the largest volcanic features on Earth. The other lines up exactly with the asteroid impact, which, in turn, may have sparked a renewed phase of volcanism in India. Surprisingly, both events are associated with extinction events of nearly equal magnitude on Seymour Island.
Dutton said they have evidence on this site on Seymour Island in Antarctica that climate change is linked to both of these extinction events, right before the boundary and right at the boundary.
"If you look at what types of species that went extinct during the first extinction pulse, they're different than the types that went extinct during the second pulse. That indicates that it may have been a different kill mechanism for those two different extinction pulses.
"It's quite likely both the volcanism and the asteroid were to blame for the ultimate mass extinction. The Deccan Traps weakened the ecosystems before the asteroid slammed into the Earth-- it's consistent with an idea called the press-pulse hypothesis: a 'one-two punch' that proved devastating for life on Earth," said Dutton.