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Fossil leaf of the willow family from the Paleocene of Colombia (58-60 million years). Photo: Daniela Carvalho/Smithsonian Tropical Research Institute

A cataclysmic asteroid strike 66 million years ago off the Yucatán Peninsula changed tropical forests in distinct ways revealed in extensive new fossil evidence.

Why it matters: The new study may help to determine how the tropical forests of South America — contributors to the global climate, rich with species and a lifeline for tens of millions of people — emerged and how they may be shaped by the pressures of climate change today.

"This single historical accident changed the ecological and evolutionary trajectory of the rainforest forever," says Carlos Jaramillo, a paleontologist at the Smithsonian Tropical Research Institute in Panama and co-author of the study published today in Science.

  • "Without the meteorite, living in the tropical forest today would be very different."

What they found: Over 12 years, Jaramillo and his colleagues collected and analyzed more than 6,000 specimens of fossilized leaves and 50,000 fossilized pollen samples in Colombia spanning the Late Cretaceous and early Paleogene period.

  • The researchers measured changes in the density of leaf veins, the diversity of insect damage and other attributes to quantify how the forest plants' diversity and structure changed from the impact.
  • Before the Chicxulub impact event, the forests were a mix of flowering plants, ferns and conifers with an open canopy that allowed light to pour into the forest.
  • After the impact, 45% of the plant species went extinct (pollen fossils for the species vanished in the record) and flowering plants came to dominate a more closed canopy, forming the forests seen today.

The big question: Why did the forests go in that new direction instead of returning to their pre-impact state, especially since the climate was similar in both periods?

Jaramillo offers three possibilities:

  • The disappearance of dinosaurs, which flattened the forest floor and fed on the canopy, reduced competition for light between plants and allowed flowering flora to take off.
  • Ash from the impact brought phosphorus to the ground, creating a rich niche for fast-growing, nitrogen-fixing flowering plants to take off. Jaramillo says the team plans to collect samples of soil preserved in rocks to measure their nutrient content.
  • Another is that conifers that evolved to be canopy trees in the tropics went extinct, whereas flowering plants were diversifying and "doing all sorts of things," he says.

The big picture: It took 6 million to 7 million years for the diversity of plants in the forest to return to levels before the collision.

  • "The lesson that comes out of these studies looking at rebuilding is that diversity doesn't come back right away," says Sean Gulick, who studies the Chicxulub impact and its effect on marine ecology at the University of Texas Institute for Geophysics and wasn't involved in the new research.
  • The findings are in line with other studies that found it took millions of years to reestablish the diversity of marine plankton after the impact, he says.

The bottom line: "The modern-day climatic crises we’re creating are geologically going to appear very fast in the record millions of years from now," Gulick says, pointing to the current rates of species extinction.

  • "We’re going to take a very long time to come back to the same level of diversity, and it is very likely it won’t look the same."

Go deeper

Updated 20 mins ago - Politics & Policy

Smaller than expected "Justice for J6" rally met with large police presence

Police officers watch as demonstrators gather for the "Justice for J6" rally in Washington, D.C., on Sept. 18, 2021. Photo: Andrew Caballero-Reynolds/AFP via Getty Images

A few hundred demonstrators were met by a heavy law enforcement presence on Saturday at the "Justice for J6" rally outside the fenced-off U.S. Capitol, AP reports.

The latest: About 400 to 450 people were inside the protest area, excluding law enforcement, U.S. Capitol Police said.

DHS to increase deportation flights to Haiti from Del Rio

Migrants walk across the Rio Grande River carrying supplies back to a makeshift encampment under the international bridge between Del Rio, Texas, and Acuña, Mexico. Officials are struggling to provide food, water, shelter and sanitation, forcing migrants to cross the Rio Grande several times per day for basic necessities. Photo: Jordan Vonderhaar via Getty Images

The Department of Homeland Security on Saturday announced plans to ramp up deportation flights to Haiti out of the small Texas border town Del Rio, starting as soon as Sunday.

Why it matters: Reports have emerged of more than 10,000 migrants, primarily from Haiti, crowded in a temporary camp under the international bridge in Del Rio. Hoping to find refuge in the United States, they've had to bear with filthy conditions and the scorching sun for days, per an NBC News affiliate.

4 hours ago - World

Pope Francis urges bishops to listen to survivors of sexual abuse

Pope Francis rides his Pope mobile through a crowd of pilgrims before holding an open-air mass on September 15, 2021 in Sastin, Slovakia. Photo: Sean Gallup/Getty Images

Pope Francis on Saturday urged European bishops to listen to survivors of clergy sexual abuse, saying "these important discussions truly touch the future of the church," AP reports.

Driving the news: Francis spoke in a video message to Central and Eastern European bishops who are convening in Poland for a four-day child protection conference beginning on Sunday.