In the long shadow of the asteroid that wiped out the dinosaurslife seems to have bounced back with surprising speed.
New analysis of sedimentation rates suggests that the first wave of marine species appeared in a few thousand years of mass extinction, several millennia faster than many scientists thought.
The results, reported on January 21 in Geologyinvite us to rethink how quickly evolution can rebuild biological diversity – not just as it did after the Asteroid Chicxulub hit Earth 66 million years ago, but perhaps also today and into the future, as climate change and other human pressures accelerate the pace of ecological upheaval.
“It really helps us understand how quickly species can evolve,” says Christopher Lowery, a paleoceanographer at the University of Texas at Austin, adding that it provides a “rare opportunity in the geologic past to understand how ecosystems can recover from these rapid and severe changes.”
The evidence comes from marine fossils known as planktonic foraminifera, microscopic single-celled inhabitants of ancient oceans encased in tiny mineral shells. The first appearance of one of these organisms – with an eloquent name Parvularuglobigerina eugubina – is an established geological timestamp marking the dawn of life’s recovery after the asteroid.
Impact of Chicxulubin what is now the Yucatán Peninsula of Mexico. This estimate came from measuring the thickness of the rock layers between the extinction horizon and the first appearance of P. eugubinathen projecting elapsed time using average sedimentation rates derived from much longer geologic intervals.Lowery himself never questioned this figure. That is, until it started to conflict with the evidence he was seeing elsewhere.
Working on sediment cores drilled from Chicxulub Crater, Lowery and his colleagues used helium-3 – a rare form of balloon-filling gas that is delivered to Earth at a nearly constant rate by interplanetary dust – to calculate how quickly sediment accumulated in Chicxulub Crater. immediately after impact.
Oddly enough, the cosmic dust indicated that P. eugubina evolved in just 6,000 years after the catastrophe that killed the dinosaurs, but Lowery was hesitant to trust the result.
He and his colleagues then turned to data published elsewhere in the world, focusing on sites where researchers had measured helium-3 and identified early post-extinction foraminifera, but had never used those measurements together to revise evolutionary chronologies.
Averaging six sites, including the Chicxulub crater and marine deposits in Italy, Spain and Tunisia, they found that the sediments took less time to accumulate than the tens of thousands of years previously estimated.
On average, the developer P. eugubina appeared 6,400 years after the impact. Other new plankton appeared in just a millennium or two. An explosion of new species quickly followed, filling empty ecological spaces left after the Chicxulub asteroid wiped out three-quarters of all plant and animal life, including most marine plankton.
The shorter timeline is important because it redefines the early Paleocene as a period of extraordinarily rapid innovation, rather than a long, slow return to catastrophe. But even Lowery’s timeline may underestimate how quickly species recovery began.
Last year, paleobiologist Brian Huber of the Smithsonian’s National Museum of Natural History and his colleagues used temperature signals encased in foraminiferal shells to show that new species of plankton have probably appeared just a few decades after the asteroid. Combining the fossil record with climate models, they concluded that after a brief darkness after the impact, when soot and dust choked the atmosphere, the skies quickly cleared. Rapid global warming followedwhich may have triggered an evolutionary change in the recovering oceans in the blink of a geological eye.
The analysis differs from Lowery’s because it relies on time frames inferred from climate models rather than direct estimates of sediment accumulation rates. But if these models capture the rate of change after impact — and, by extension, the emergence of new species — then “oh my God, it’s even faster than suggested,” Huber says. “It’s a real eye-opener.”
Together, these results highlight how quickly biology can innovate after a calamity. “Life really starts to bounce back as soon as there is a chance,” says Vivi Vajda, a paleobiologist at the Swedish Museum of Natural History in Stockholm, who was not involved in the research.
But even rampant speciation can’t quickly cure a mass extinction, Lowery says, pointing out that it still took millions of years for ecosystems to fully recover — and that nothing like the dinosaurs ever returned.
Evolution, it seems, is capable of sudden outburst, but not of instant repair.
