In the long shadow of the asteroid that wiped out the dinosaurs, life appears to have bounced back with surprising speed.
A new analysis of sedimentation rates suggests that the first wave of marine species emerged within a few thousand years of the mass extinction event, many millennia quicker than many scientists assumed.
The findings, reported January 21 in Geology, invite a rethink of how rapidly evolution can rebuild biological diversity — not just as it did after the Chicxulub asteroid struck 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.
“This 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 geological past to understand how ecosystems can recover from these quick, severe changes.”
The evidence comes from marine fossils known as planktonic foraminifera, microscopic single-celled denizens of the ancient oceans encased in tiny mineral shells. The first appearance of one such organism — with the tongue-twisting name Parvularugoglobigerina eugubina — is an established geological time stamp marking the dawn of life’s recovery after the asteroid.
A widely cited 2011 estimate placed that time stamp at roughly 30,000 years after the Chicxulub impact, in what is today the Yucatán Peninsula of Mexico. That estimate came from measuring the thickness of rock layers between the extinction horizon and the first appearance of P. eugubina, then projecting the elapsed time using average sedimentation rates derived from far longer geological intervals.
Lowery himself never questioned that figure. That is, until it began to clash with evidence he was seeing elsewhere.
Working on sediment cores drilled from the Chicxulub crater, Lowery and colleagues used helium-3 — a rare form of the balloon-filling gas that is delivered to Earth at a nearly constant rate by interplanetary dust — to calculate how quickly sediments accumulated in the immediate aftermath of the impact.
Curiously, the cosmic dust indicated that P. eugubina evolved within just 6,000 years of the dino-killing catastrophe, but Lowery hesitated to trust the result.
He and his colleagues then turned to published data from elsewhere in the world, focusing on sites where researchers had measured helium-3 and identified the first post-extinction foraminifera, but had never used those measurements together to revise evolutionary timelines.
Averaging across six sites — including the Chicxulub crater and marine deposits from Italy, Spain and Tunisia — they found the sediments had actually taken less time to build up than the tens of thousands of years previously estimated.
On average, the telltale P. eugubina appeared 6,400 years after the impact. Other new plankton showed up within just a millennium or two. A burst of new species quickly followed, filling the empty ecological spaces left behind after the Chicxulub asteroid annihilated three-quarters of all plant and animal life, including most marine plankton.
The shorter timeline matters because it recasts the early Paleocene epoch as a period of extraordinarily rapid innovation, rather than a long, slow crawl back from catastrophe. But even Lowery’s timeline may understate 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 locked inside foraminifera shells to show that new plankton species likely emerged within just decades of the asteroid. Pairing the fossil record with climate models, they concluded that, following a brief post-impact darkness, when soot and dust choked the atmosphere, the skies quickly cleared. Rapid global warming followed, which may have jump-started evolutionary change in the recovering oceans in the blink of a geological eye.
The analysis differs from Lowery’s, resting on inferred timing from climate models rather than direct estimates of sediment accumulation rates. But if those models capture the pace of post-impact change — and, by extension, the emergence of new species — then “oh my gosh, it’s even faster than suggested,” Huber says. “It’s a real eye-opener.”
Together, the findings underscore just how quickly biology can innovate after calamity. “Life really starts to rebound as soon as there is any possibility,” says Vivi Vajda, a paleobiologist at the Swedish Museum of Natural History in Stockholm who was not involved in the research.
But even breakneck speciation cannot swiftly remediate a mass extinction, says Lowery, noting that it still took millions of years for ecosystems to fully recover — and nothing like the dinosaurs ever returned.
Evolution, it seems, is capable of sudden brilliance, but not of instant repair.
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