The origin of the Amazon, as well as modern tropical forests, may be a consequence of the impact of the large asteroid that fell on Earth in the late Cretaceous period and extinguished the dinosaurs. The conclusion is from a study published last week (2) in the journal Science.
According to the scientists, before the terrible 12 km wide rocket hit the Yucatán peninsula in Mexico, the rainforests of South America were made up of a type of vegetation very different from the exuberance of flowering plants that now exist. The forest was “an open canopy with many ferns, many conifers and dinosaurs”, says a study author, Carlos Jaramillo.
Jaramillo and his colleagues at the Smithsonian Tropical Research Institute analyzed tens of thousands of samples of fossil pollen and leaves found in Colombia, dating from the Cretaceous period just before the asteroid collision, and other samples from the Paleocene period, after the asteroid crash. .
Why did the impact of the asteroid give rise to the current rainforest?
The lead researcher for the project, Dr. Mónica Carvalho explained to the BBC that, after examining more than 50 thousand fossil pollen records and more than 6 thousand leaf fossils, before and after the impact, the team started to work with three different hypotheses.
The first one proposes that the huge herbivorous sauropods, those necked dinosaurs that we see in the movies, could have prevented the forests of that time from becoming too dense, feeding on or trampling on the plants that grew at the lowest levels.
A second explanation concerns the ashes that fell from the sky after the impact. According to the researchers, these residues may have acted as a kind of fertilizer to create a soil rich in nutrients. This fact allowed the forest to recover over the next six million years.
The third hypothesis also refers to the substitution of species: the particular extinction of conifers, which left areas open and illuminated by the sun, created an opportunity for flowering plants (angiosperms) to take their place. From there, the treetops became thicker, reducing the amount of sunlight reaching the ground.
Importance of research
For paleontologist Elena Stiles, from the University of Washington, Seattle, USA, who did not participate in the research, the importance of this study is to provide a comprehensive explanation of what may have happened in tropical ecosystems shortly after the extinction of the dinosaurs. Until then, she told Science magazine, studies were limited to North American forests and, at most, Patagonia.
The study also answers the basic question of “where does all this diversity” of species come from, a question that, according to Stiles, was justified by the climate of the continent or its isolation from other regions. Therefore, putting the extinction event as one of the mechanisms that shaped this important ecosystem “is really interesting”, says the paleontologist.
In some places studied, said Carlos Jaramillo, it was possible to observe “how this forest that took 66 million years to be formed ended in one day”. This rate of deforestation is impressive, he says, because the study shows the absurd amount of time it takes to rebuild a forest with such diversity.