Earth entered its ‘bad decades’ after dinosaur-ending asteroid strike

Decades of chaos and destruction, filled with devastating earthquakes and tsunamis, followed the asteroid strike 66 million years ago that wiped out all dinosaurs apart from birds. The long-term global chaos inflicted by the Chicxulub asteroid, which was up to 15 kilometres in diameter and struck what is now the Gulf of Mexico, has been revealed through analysis of sediments preserved on the New Jersey coast, thousands of kilometres away from the impact crater. It has become increasingly apparent in recent years that the asteroid’s effects weren’t confined to a single, disastrously bad day, but instead lasted a lot longer. For instance, the deformation of the crust to a depth of 35 kilometres left the impact site hot for millions of years. Advertisement It is also now thought that in the shorter term, a catastrophic maelstrom of fire engulfed much of the planet as debris that was hurled into space rained back down on Earth, burning up as it re-entered the atmosphere. “Earth’s ‘bad day’ is when the Chicxulub impact occurred,” says Kenneth Miller at Rutgers University in New Jersey. “However, that was just the beginning of the story.” The asteroid strike unleashed an earthquake felt around the world that was between magnitude 10 and 11, creating tsunamis that may have been a kilometre high close to the impact zone. “Chicxulub rung the bell of the planet, and then it continued to ring for decades,” says Miller. “These deposits in New Jersey change our view about how long organisms were exposed to extremely detrimental environmental degradation,” he says. “That’s a fancy professor way of saying shit was really bad for 20 years.” The researchers took rock cores from multiple sites on the New Jersey coastal plain, more than 2500 kilometres from the impact crater, to study the geology in the area in the years following the disaster. These cores show that sediment layers deposited after the fallout from the asteroid were mixed and remobilised multiple times. Such reworking of deposits is only possible through large, ongoing earthquakes and tsunamis, says Miller. Possibly more than a dozen aftershocks, which may have been in the order of magnitude 7 and 8, were felt on the New Jersey coast alone. Miller and his colleagues say the cores recovered from New Jersey record the transition from the catastrophic moments following the Chicxulub impact right through to a longer-term disruption, a period they have now named Earth’s “bad decades”. Another intriguing finding from the New Jersey cores is the presence of large quantities of kaolinite, which normally forms over centuries from weathering in tropical regions, but may have formed in just years at the team’s study sites. This could have been due to the presence of vast amounts of fungi, which can accelerate the formation of kaolinite, says Miller. The team speculates this is possible evidence that, during the nuclear winter-like conditions thought to have followed the impact, much of the planet’s vegetation died, providing a veritable feast for microorganisms. The team has developed a new timeline for the first 20 years post-asteroid, beginning with the extraordinary and dramatic events of the first day. This was followed by dust settling back to Earth from the atmosphere, leading to near-complete darkness for up to three years, followed by nuclear winter-like conditions for up to 20 years and fungal proliferation. All the while, the planet was beset by aftershocks and tsunamis. “New Jersey preserves one of the highest-resolution records yet recovered of the first decades after Chicxulub, allowing researchers to resolve environmental and geological processes year-by-year to decade-by-decade, rather than viewing the aftermath as a single catastrophic instant,” says Miller. Craig O’Neill at Queensland University of Technology, Australia, says the team has presented a record that “lets us really unpick what was going on immediately after the impact”. “This builds on a long compendium of work globally suggesting that the environmental and biological impacts of ‘mega-events’ like Chicxulub go far beyond the impact blast itself,” he says. Chris Kirkland at Curtin University, Australia, says the site records processes that operated over years to decades after the impact, rather than simply its immediate aftermath. “The really interesting aspect of the study is the potential to resolve not just the immediate consequences of the impact, including ejecta fallout, sediment reworking and tsunami-related processes, but the longer-lasting environmental disturbance,” he says. Annemarie Pickersgill at the University of Glasgow, UK, says the New Jersey findings provide further evidence for long-term seismicity also recorded in other regions of Earth. “These [New Jersey] sites preserve a detailed record of the geological and environmental conditions in the decades following the Chicxulub impact, providing new insights into the aftereffects of a very large impact event,” she says. EarthArXiv DOI: 10.31223/X5Z215