It takes millions of years for life to fully recover from a catastrophic extinction event, according to a new study that examined the aftermath of the asteroid strike that wiped out all non-avian dinosaurs 66 million years ago. The study sheds light on an apparent speed limit to recovery in the wake of a mass extinction, and could help us understand how long it could take life to rebound from the effects of climate change.
Over the course of its 4.5 billion year history, planet Earth has played host to a phenomenal array of life, from early microscopic organisms to enormous dinosaurs, and eventually, to us. The world we live in today is shaped not only by the emergence of life, but also by the wholesale destruction of it in cataclysmic mass extinction events.
Without doubt the most well known of these events was the asteroid impact that wiped out all of the land-based dinosaurs, and triggered dramatic environmental changes. But there have been others. For example, some 252 million years ago there was an event known as the "Great Dying," during which almost all of the life in Earth's oceans was decimated.
Fossil records from each of these events reveal an apparent lag or speed limit that nature places on the recovery of life following an extinction. Earlier research suggested that the reason for the delay was rooted in environmental factors, however a new study authored by researchers from the University of Texas in Austin and the University of Bristol located in the UK, suggests that the culprit for the hold-up may be evolution itself.
The researchers studied fossils of foraminifera, or forams – a type of plankton that lived in Earth's ancient seas. Foram fossils are exceptionally useful to scientists tracking long term species change, as their prevalence in ocean sediment allows scientists to observe their progression over vast swathes of time without any interruptions.
Although foram populations were devastated by the asteroid impact that wiped out the dinosaurs, some species were able to survive. The team behind the new study tracked their recovery focusing on the 20 million years that covered the violent event and subsequent rebound.
The Cretaceous-Paleogene extinction is the only event in Earth's history that caused worldwide change to life faster than the currently unfolding effects of anthropogenic climate change. Therefore, studies examining the event could prove to be a valuable resource for understanding how species may rebound in the future.
The team discovered that surviving foram species quickly reacted to their new situation to fill ecological niches. However, after this initial step forward progress was delayed, as the forams in their new roles adapted and became more complex, and evolved a new stockpile of special traits that then led to species diversification. These new innovations would allow the forams to further fill their ecological niches, or even create entirely new ones to inhabit.
It took roughly 10 million years for foram species diversity to recover to levels comparable to pre-extinction levels.
The idea that evolution may be the bottleneck to the recovery of life was first proposed 20 years ago, but according to the authors of the study, their work represents the first time evidence has been discovered in the fossil record to back up the theory.
Furthermore, the researchers believe that their findings likely hold true for other extinction events and could even inform how fast life will recover from the effects of climate change, habitat destruction and other threats.
"We're hoping that examining the rest of the planktic foraminiferal record will give us insight into how climate shaped their evolution," said co-author of the new study Andrew Fraass, a research associate at the University of Bristol. "With the past, slower changes in climate we have in the geological record, we should be able to tease out more details about how climate change might impact these important plankton."
The paper has been published in the journal Nature Ecology and Evolution.
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