Colombia’s rainforest looked very different 66 million years ago. Currently, the humid and biodiverse ecosystem is full of plants and is covered in a thick canopy of leaves and branches, which blocks light. In particular, there are no dinosaurs. But before the dinosaurs disappeared with the impact of Chicxulub, signaling the end of the Cretaceous period, things looked very different. The cover of plants in the area was relatively low, and a lot of conifers called it home.
Using the fossilized remains of the plants, a team of researchers studied the past of the rainforest and how the asteroid gave rise to today’s rainforests. The study, published in Science on April 1, it was led by scientists at the Smithsonian Tropical Research Institute (STRI) in Panama and supported by scientists at the Negaunee Institute for Plant Conservation and Action at the Chicago Botanical Garden.
“Forests have disappeared due to the ecological catastrophe … and then the vegetation that has returned has been largely dominated by flowering plants,” said Mónica Carvalho, first author and joint postdoctoral fellow at STRI and the Universidad del Rosario in Colombia. , in an interview with Ars.
The research began 20 years ago, with parts of the team collecting and analyzing 6,000 leaves and 50,000 pollen fossils from Colombia. Looking at these fossils, the team was able to understand the types of plants present both before and after the asteroid hit the planet. This sequence represents the region’s biodiversity between 72 and 58 million years ago, covering both before and after the impact. “It took us a long time to gather enough data to have a clear picture of what was happening during the disappearance,” Carvalho told Ars.
While the study covers Colombian fossils, Carvalho said researchers may have a correct idea of what happened in tropical forests in other parts of Central and South America, although the effects of the asteroid’s impact are somewhat variable from one region to another. other. “It simply came to our notice then. We still don’t know why some places were affected more than others, “she said.
After the asteroid hit Earth, nearly half of Columbia’s plant species perished – pollen fossils for those species ceased to appear after that point. The rainforest has begun to be taken over by ferns and flowering plants that, although they had an impact before, were less common than they are today. In comparison, coniferous trees have actually disappeared.
Beyond the presence of conifers, the rainforests of the past were probably much rarer than their modern counterparts. Today’s rainforests have thick canopies, and the plants in them are spaced apart, which means that more plants sweat water into the atmosphere. This leads to higher levels of humidity and cloud cover. According to Carvalho, the relative lack of moisture in earlier forests means that the regions were probably much less productive than they are today.
But the forest with lower productivity remained in place until it hit the asteroid. “Only after the impact do we see that the forests are changing their structure,” she said.
Researchers have some hypotheses about how this change occurred. The first is that the death of the dinosaurs made the forests denser – there could have been fewer animals that ate the plants or trampled on the brush, allowing the leaves to grow relatively uncontrollably. The second idea is that shortly after the asteroid collided with the planet, there was a selective disappearance of conifers in the tropics – they could simply have gone less well than their flowering colleagues after the impact.
The third is that the aftermath of the catastrophe could have fertilized the soil. The post-impact tsunami events could have transported debris and sediment from deep, carbon-rich marine areas. Burning fires could have sent ash into the atmosphere, and when it finally settled on the ground, it could have acted as a kind of fertilizer. Flowering plants tend to grow better than conifers in nutrient-rich soils, Carvalho said. She also mentioned that all these hypotheses, or any of them, could be simultaneously true.