Asteroid that killed the dinosaurs gave us today's tropical rainforests: study

Serrania de Chiribiquete National Natural Park, Colombia. (© WWF Colombia)

TORONTO — About 66-million years ago, the asteroid most known for killing the dinosaurs set off another chain of events that would pave the way for modern tropical rainforests and flowers to grow, according to a new study.

Researchers aimed to find the evolution of modern rainforests by studying tropical plant fossils. The study, conducted by researchers at the Smithsonian Tropical Research Institute (STRI), found that along with the dinosaurs, 45 per cent of plants in what is now Colombia went extinct.

“We wondered how tropical rainforests changed after a drastic ecological perturbation such as the Chicxulub impact, so we looked for tropical plant fossils,” Monica Carvalho, first author, said in a press release. “Our team examined over 50,000 fossil pollen records and more than 6,000 leaf fossils from before and after the impact.”

By studying the pollen fossils, the researchers were able to determine that plant diversity in the area didn’t recover for nearly 10 million years after the impact, the press release said, but as it recovered, flowering plants and trees became dominant.

They used leaf fossils to judge the climate and environment of pre- and post-impact forests and they found that it rained just as much then as it does now.

“It was just as rainy back in the Cretaceous, but the forests worked differently,” Carvalho said.

The study found that before the mass extinction event, rainforests looked very different. They were made up of mostly ferns and conifer plants, relatives of the pine trees bought and sold at Christmastime. Now, rainforests are complete with tall, flowering trees in a variety of colours.

The researchers have three theories as to how the asteroid impact changed rainforests into the dense flowering forests of modern times.

One theory is that the dinosaurs kept the pre-impact forests sparse by their feeding and movements through them.

The second is that the ash from the impact enriched the soils and gave way to faster growing plants.

The third is that the extinction of the once-thriving conifer plants gave flowering plants an opportunity to thrive.

“Our study follows a simple question: How do tropical rainforests evolve?” Carvalho said. “The lesson learned here is that under rapid disturbances—geologically speaking—tropical ecosystems do not just bounce back; they are replaced, and the process takes a really long time.”