Dinosaurs and fossil aficionados have strong knowledge of the meteorite strike that wiped out Tyrannosaurus rex and all nonavian dinosaurs extinct around 66 million years ago. But it is often overlooked that the impact was also destroying whole ecosystems. A new study shows how these casualties, as a result, produced another unique evolutionary product: the emergence of the Amazon rainforest in South America, the most amazingly diverse environment on the planet. But now the threat from Amazon’s tropical species and habitats is now due to the unprecedented destruction of human activity, including the clearing of land for agriculture.
The new study, published Thursday in Science, analyzed tens of thousands of plant fossils and represents “fundamental advances in knowledge,” said Peter Wilf, a geologist at Pennsylvania State University, who involved in the research. “The authors confirm that the extinction of dinosaurs is also a major resettlement event for neotropical ecosystems, putting their evolution on a completely new path leading directly to the rainforests. amazing, diverse, amazing and in great danger in the area today. “
These comments, Wilf adds, “provide a new impetus for the conservation of a living evolutionary heritage in the tropics that supports human life, along with millions of living species.”
Carlos Jaramillo, a paleobiologist at the Smithsonian-based Tropical Research Institute and co-lead author of the study, agrees that the evolutionary and ecological impact of the meteorite is affecting today’s rapid, human destruction of forest Amazon water and other key habitats. across the planet. “We can relate this to today,” he said, “because we are also changing landscapes, and that will last forever – or at least for a long time.”
Examination of some 50,000 pollen grains and 6,000 fossil leaves reveals that the meteorite caused the extinction of nonavian dinosaurs in the Amazon rainforest.
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Today’s rainforests are essential for life on Earth. The Amazon, in particular, plays an important role in regulating the planet’s freshwater cycle and climate. But paleontologists in western Europe and North America have paid little attention to tropical forests, focusing their place on medium latitudes. Many academic and amateur fossil hunters have also described warm, wet areas as a lost cause for discovery because they have accepted that conditions there would prevent the preservation of organic matter. Long enough for fossils. “It was this combination of factors that led us to the lack of data in the tropics,” says Bonnie Jacobs, a paleobiologist at Southern Methodist University, who co-wrote an essay in a context published by the new study in the Science.
Scientists already knew that the effects of the meteorite crash and its aftermath – at least in temperate zones – varied according to local conditions and distance from the Chicxulub impact crater in the Yucatan Peninsula in Mexico. The forests of New Zealand, for example, escaped unscathed. But researchers had no idea how the event changed Africa’s tropical rainforests or, so far, South American ones.
Along with most of his co-authors, Jaramillo is from Colombia and was particularly keen to explore the origins of his country’s tropical forests. The new study, which he thought of as an undergraduate student, represents nearly 12 years of effort. “It took us a long time,” he says, “because we had to start from zero.”
Almost whole trees are preserved in the fossil record, so Jaramillo and his colleagues turned to fossil pollen and left for views. Pollen retains well over time and is abundant in the fossil record. Like leaves, it differs morphologically among species, which helps researchers determine which types of plants lived in an ancient habitat.
Jaramillo and his colleagues explored 53 sites across Colombia for rocks formed during the Late Cretaceous period, just before the meteorite strike, and others formed during 10 million years later, in the Paleogene period. From these rocks, the team collected and produced approximately 50,000 fossil pollen grains and 6,000 fossil leaves to identify the types of plants they produced. Recent individual findings show that the leaves of plants that receive more light have a higher density of vines, as well as a higher ratio of naturally occurring isotopes known as carbon 13. The researchers studied these features among the collected fossils to bring together the historical structure of the area. woods.
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Their findings paint a picture of a sudden, cataclysmic life of life after the impact – but also of a phoenix-like rebirth in millions of years afterward. Before the meteorite arrived, the authors concluded, there were many conifers in South American forests and an open canopy with bright light supporting a warm base of ferns. Dinosaurs seem to have played a key role in maintaining these Cretaceous forests by felling trees and clearing vegetation, among other things. Within times of the impact of the Chicxulub meteorite, however, this ecosystem was inexorably altered. Fires, which were likely to burn for several years, broke into the forests of southern South America. Along with many of the animals they supported, 45 percent of the continent’s tropical plant species disappeared, according to the authors ’calculations.
It took six million years for the forests to return to their pre-meteorite diversity, and the species that grew back were completely different than before. Legumes – plants that form symbiotic relationships with bacteria that allow them to fix nitrogen from the air – were the first to emerge, and enriched the nutrient-poor soil. This flow of nitrogen, along with phosphorus from meteorite ash, allowed other flowering plants to thrive alongside the legumes and conifers. As flowering species competed for light, they formed thick canopies of leaves and created the linear rainforest of the Amazon we know today, marked by a blanket of productivity above and a dark basement at the bottom.
Regan Dunn, a paleoecologist at La Brea Tar Museum and Museum in Los Angeles, who was not involved in the new study, agrees that his findings are not just to reflect the past but also for putting conventional anthropogenic threats into view. In particular, the authors’ calculation notes that 45 per cent of plant species became extinct after the meteorite strike, as “conventional estimates suggest that at least many plant species are endangered. worldwide in the Amazon basin in the next 30 years of human-only activity. ”
“The question remains: How will human influence change the shape and function of Amazonian forests forever?” Dunn says.
The new findings show how major events can become “the course of everything,” Jacobs says. Today we are in the middle of another such event, she said, but this one is driven by one gender – and is nowhere near the metaphorical impact crack “because humans are ubiquitous.”
But unlike major events that have gone before, Jacobs says, this time “we have no power to stop it.”