Colombia’s rainforest appeared very totally different 66 million years in the past. At current, the humid and biodiverse ecosystem is jam-packed with vegetation and is roofed in a thick, light-blocking cover of leaves and branches. Notably, there aren’t any dinosaurs. But previous to the dinosaurs going away with the Chicxulub affect, signaling the tip of the Cretaceous interval, issues appeared very totally different. The space’s plant protection was comparatively sparse, and a bevy of conifers known as it residence.
Using the fossilized stays of vegetation, a crew of researchers studied the previous of the rainforest and the way the asteroid gave rise to the rainforests of right this moment. The research, revealed in Science on April 1, was led by scientists on the Smithsonian Tropical Research Institute (STRI) in Panama and supported by scientists on the Negaunee Institute for Plant Conservation Science and Action on the Chicago Botanic Garden.
“Forests disappeared because of the ecological catastrophe… and then, the returning vegetation was mostly dominated by flowering plants,” mentioned Mónica Carvalho, first creator and joint postdoctoral fellow at STRI and on the Universidad del Rosario in Colombia, in an interview with Ars.
The analysis started 20 years in the past, with elements of the crew amassing and analyzing 6,000 leaf and 50,000 pollen fossils from Colombia. Looking at these fossils allowed the crew to get a way of the kinds of vegetation current each earlier than and after the asteroid struck the planet. This sequence represents the area’s biodiversity between 72 million and 58 million years in the past, overlaying each earlier than and after the affect. “It took us a long time to gather enough data that we could have a clear picture of what was going on during the extinction,” Carvalho advised Ars.
While the research offers with Colombian fossils, Carvalho mentioned the researchers can get a good concept of what occurred in rainforests elsewhere in Central and South America, although the results of the asteroid’s affect are considerably variable from area to area. “It’s a little bit variable. We still don’t know why some places were affected more than others,” she mentioned.
After the asteroid hit the Earth, almost half of the plant species in Colombia perished—the pollen fossils for these species stopped showing previous that time. The rainforest started to be taken over by ferns and flowering vegetation that, whereas current pre-impact, have been much less frequent than they’re right this moment. The coniferous bushes, by comparability, successfully died out.
Beyond the presence of conifers, the rainforests of the previous have been probably a lot sparser than their fashionable counterparts. Current rainforests have thick canopies, and the vegetation inside them are spaced intently collectively, which means extra vegetation are transpiring water into the environment. This results in larger ranges of humidity and cloud protection. According to Carvalho, the relative lack of humidity in earlier forests implies that the areas have been probably a lot much less productive than they’re right this moment.
But the lower-productivity forest remained in place till the asteroid hit. “It was only after the impact that we see the forests change their structure,” she mentioned.
The researchers have some hypotheses about how this transformation occurred. The first is that the demise of the dinosaurs prompted the forests to develop extra dense—there may have been fewer animals consuming the vegetation or stomping by way of the comb, permitting foliage to develop comparatively unchecked. The second concept is that, shortly after the asteroid collided with the planet, there was a selective extinction of conifers within the tropics—they may have merely fared much less properly than their flowering friends post-impact.
The third is that the aftermath of the disaster may have fertilized the soil. Tsunami occasions that occurred after the affect may have carried particles and sediment from carbon-rich, shallow marine areas close by. Burning wildfires may have despatched ash into the environment, and when it lastly settled on the bottom, it may have acted as a sort of fertilizer. Flowering vegetation are inclined to develop higher than conifers in high-nutrient soils, Carvalho mentioned. She additionally famous that every one of those hypotheses, or any two of them, may concurrently be true.