Deep earthquakes could also rattle magma chambers and lead to more eruptions
A long-running debate about the relative importance of an asteroid impact versus the effects of large-scale vulcanism on an ancient mass extinction event may be moot.
A new study by University of California Berkely geologists suggests that both are related. An asteroid impact on Earth may have accelerated volcanic eruptions some 66 million years ago, and together, the planet-wide catastrophes caused the extinction of many land and marine animals, including the dinosaurs.
The study includes the most accurate dates yet for the volcanic eruptions before and after the impact. The new dates show that the Deccan Traps lava flows, which at the time were erupting at a slower pace, doubled in output within 50,000 years of the asteroid or comet impact that is thought to have initiated the last mass extinction on Earth.
Both the impact and the volcanism would have blanketed the planet with dust and noxious fumes, drastically changing the climate and sending many species to an early grave.
“Based on our dating of the lavas, we can be pretty certain that the volcanism and the impact occurred within 50,000 years of the extinction, so it becomes somewhat artificial to distinguish between them as killing mechanisms: both phenomena were clearly at work at the same time,” said lead researcher Paul Renne, a UC Berkeley professor-in-residence of earth and planetary science and director of the Berkeley Geochronology Center. “It is going to be basically impossible to ascribe actual atmospheric effects to one or the other. They both happened at the same time.”
The geologists argue that the impact abruptly changed the volcanoes’ plumbing system, which produced major changes in the chemistry and frequency of the eruptions. After this change, long-term volcanic eruptions likely delayed recovery of life for 500,000 at the end of the Cretaceous and the beginning of the Tertiary period when large land animals and many small sea creatures disappeared from the fossil record.
“The biodiversity and chemical signature of the ocean took about half a million years to really recover … which is about how long the accelerated volcanism lasted,” Renne said. “We are proposing that the volcanism unleashed and accelerated right at the KT boundary suppressed the recovery until the volcanoes waned.”
Co-author Mark Richards, a UC Berkeley professor of earth and planetary science, said the link between the impact and the flood basalts is becoming harder to deny.
“If our high-precision dates continue to pin these three events – the impact, the extinction and the major pulse of volcanism – closer and closer together, people are going to have to accept the likelihood of a connection among them. The scenario we are suggesting – that the impact triggered the volcanism – does in fact reconcile what had previously appeared to be an unimaginable coincidence,” he said.