Colombia’s rainforest looked 66 million years ago very different. At present, the moist and biodiverse ecosystem is chock-full of plants and is covered with a thick, light-blocking foliage of leaves and branches. In particular, there are no dinosaurs. But before the dinosaurs leave with the Chicxulub impact, which marks the end of the Cretaceous, it looks very different. The area’s plant cover was relatively sparse, and a mighty conifer calls it home.
Using the fossilized remains of plants, a team of researchers studied the past of the rainforest and how the asteroid gave rise to the rainforests of today. The study, published in Science led on April 1 by scientists from the Smithsonian Tropical Research Institute (STRI) in Panama and supported by scientists from the Negaunee Institute for Plant Conservation Science and Action at the Chicago Botanic Garden.
“Forests have disappeared due to the ecological catastrophe … and then the recurring vegetation has mostly been dominated by flowering plants,” Mónica Carvalho, first author and co-postdoctoral fellow at STRI and at the Universidad del Rosario in Colombia, said in an interview with Ars.
The research began 20 years ago, with parts of the team collecting and analyzing 6,000 leaf and 50,000 pollen fossils from Colombia. By looking at these fossils, the team was able to get an idea of the types of plants that were present before and after the asteroid hit the planet. This series represents the biodiversity of the region between 72 million and 58 million years ago, covering both before and after the impact. “It took us a long time to gather enough data to get a clear picture of what was going on during the extinction,” Carvalho told Ars.
While studying Colombian fossil fuels, Carvalho said researchers could get a good idea of what happened in rainforests elsewhere in Central and South America, although the effects of the asteroid’s impact vary from region to region. is. “It’s a little variable. “We still do not know why some places are affected more than others,” she said.
After the asteroid hit Earth, nearly half of the plant species in Colombia perished – the pollen fossils for those species stopped appearing beyond that point. The rainforest was taken over by ferns and flowering plants which, although currently before the impact, were less common than today. The conifers effectively became extinct by comparison.
Aside from the appearance of conifers, the rainforests of the past were probably slimmer than their modern counterparts. Current rainforests have thick canopies, and the plants in them are now separated from each other, which means that more plants carry water to the atmosphere. This leads to higher humidity levels and cloud cover. According to Carvalho, the relative lack of moisture in earlier forests means that the regions were probably much less productive than today.
But the lower productivity forest remained in place until the asteroid hit. “It was only after the impact that the forests changed their structure,” she said.
The researchers have some hypotheses about how this change occurred. The first is that the downfall of the dinosaurs made the bushes denser – fewer animals could have digested the plants or bumped through the brush, which could cause the leaves to grow relatively unnoticed. The second idea is that, shortly after the asteroid collided with the planet, there was a selective extinction of conifers in the tropics – they could have fared less well than their flower companions after the impact.
The third is that the aftermath of the disaster could fertilize the ground. Tsunami events that occurred after the impact could carry debris and sediment from carbon-rich, shallow marine areas in the area. Burning wildfires could send ash into the atmosphere, and when it eventually sank to the ground, it could act as a kind of fertilizer. Flowering plants tend to grow better than conifers in soil rich in nutrients, Carvalho said. She also noted that all of these hypotheses, or any two of them, may be true at the same time.