Asteroid that decimated dinosaurs gave birth to the Amazon, says study | News from science to improve the quality of life | DW

The impact of the asteroid that decimated the dinosaurs 66 million years ago helped to give rise to the tropical forests we know today, pointed out a study published in the scientific journal Science this Friday (02/04).

Researchers analyzed tens of thousands of pollen fossils, spores and leaves to understand how the asteroid collision affected the rainforests of South America. These fossils were collected at 39 locations across Colombia and date from 70 million to 56 million years ago. back.

Scientists concluded that after the huge space rock hit Earth, wiping out more than 75% of life on the planet, the type of vegetation that formed these forests has also changed dramatically.

Before the collision, the tropical forest that thrived in Colombia consisted of flowering shrubs bathed in sunlight, which in turn flowed through large crevices between the tops of tall conifers. After the asteroid, this open canopy forest was transformed into the dense, dark forests of the Amazon that we know today, say the scientists.

When analyzing the fossils collected, the study found that the diversity of plants decreased by 45% immediately after the fall of the space rock. After the event, it took 6 million years for the rich diversity of the rainforest to recover. Even so, the forest was never the same.

“A single historic accident changed the ecological and evolutionary trajectory of tropical forests,” says Carlos Jaramillo, a researcher at the Smithsonian Tropical Research Institute in Panama City. “The forests that we have today are really the by-product of what happened 66 million years ago.”

Before, tropical forests were a mixture of angiosperms, or flowering trees and shrubs, and other plant species, such as conifers and ferns. “The competition for light was not so intense,” explains Jaramillo, who is a paleoecologist, a field of science that studies fossils to reconstruct ecosystems of the past.

Then, ferns and conifers largely disappeared, and angiosperms came to represent about 90% of forest plant species.

Why changed?

The reasons are not entirely clear, say the scientists in the study. The region’s climate at the end of the Cretaceous period, 66 million years ago, was similar to today: hot and humid. But other factors were probably at play.

Huge herbivorous sauropods, the long-necked dinosaurs, would have helped to keep the gaps open between the trees, allowing light to enter, says Jaramillo. As soon as the asteroid hit Earth, the dinosaurs left the scene. According to the researcher, the extinction of certain families of plants due to the impact may also have influenced it.

A third probable factor was a change in the chemical composition of the forest soil. The frequent rains during the hot and humid Cretaceous removed many nutrients from the soil, which would have favored the existence of gymnosperms such as conifers.

“Gymnosperms had this incredible ability to grow with very little food and could beat angiosperms,” ​​explains Jaramillo.

According to the team, the ashes that fell after the impact of the asteroid may have added phosphorus to the soil, effectively fertilizing them. With more food available, angiosperms outnumbered gymnosperms, growing rapidly towards the sky and blocking sunlight.

This thick, closed canopy appeared shortly after the impact, but the forest diversity took much longer to recover, as new species began to evolve to occupy new ecological niches.

For researcher Jaramillo, this long road to recover the forest brings an important alert to the lasting impact of modern human activities, such as deforestation. “Generating new diversity takes geological time,” he says. “It is not just about planting trees.”

The importance of research

In an interview with Science, paleoecologist Elena Stiles, of the University of Washington in Seattle, who did not participate in the study, says the research is the first to bring a comprehensive idea of ​​what happened in tropical ecosystems shortly after the extinction of the dinosaurs. According to her, most studies on the event involve forests in North America or further south, as in Patagonia, but not in the tropics.

For Stiles, it is also impressive that the discovery could help answer a long-standing question about South America’s surprising biodiversity.

“People have long wondered where all this diversity comes from,” says the scientist. Researchers have already speculated, for example, that the continent’s climate or its long isolation from other regions may be responsible. “So it is really interesting that this mass extinction event may have been one of the mechanisms that shaped it to be this unique region.”

ek (ots)

  • Unraveling the reefs of the Amazon

    An unlikely reef

    A scientific mission travels the northern coast of Brazil to French Guiana. Brazilian scientists from UFPA, UFRJ, USP and UENF research coral in the Amazon, practically unknown to science. They form the largest reef in Brazil, are found from 70 meters to 220 meters deep and have the potential to house new species.

  • Ship Esperanza Greenpeace

    Unraveling the reefs of the Amazon

    Esperanza on scientific mission

    Scientists are aboard Greenpeace’s Esperanza. With 72 meters in length, he traveled from Bordeaux, in France, to Belém, in Pará. The vessel left the Brazilian port for the scientific mission in the beginning of April and, until May, it traverses the Atlantic area that is influenced by the Amazon River. .

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    On-board technology

    The current mission investigates the so-called northern sector of the Amazon reef, where Total and BP are awaiting a license to explore for oil. The side-scan sonar makes a “reading” of the ocean floor. It emits acoustic waves that are transformed into images that are analyzed simultaneously, with the help of researcher Mirella Borba Costa, from USP.

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    Unraveling the reefs of the Amazon

    Robot in action

    When the researchers locate an interesting point after using the sonar, it is time for the robot to make images and collections. It is an ROV (Remotely Operated Vehicle). The equipment can reach 2 thousand meters in depth and is equipped with three cameras that transmit images in real time. Special coupled bottles collect water, and mechanical arms, material.

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    Unraveling the reefs of the Amazon

    The secret of bacteria

    In parallel, the research work takes place on board the ship. In the photo, a preparation of the culture medium will allow only vibri, a type of bacteria, to grow. In the university’s laboratory, genetic sequencing will be carried out and the researchers will try to understand the role of this bacterium in the corals of the Amazon.

  • Atlantic spotted dolphins (Stnella frontalis)

    Unraveling the reefs of the Amazon

    Visitors

    During the expedition, dolphins are spotted swimming near the ship. These are called Atlantic spotted dolphins (Stnella frontalis). In this region of the ocean, on the north coast of Brazil, turtles, whales, various types of crustaceans and fish are also found. In the coral region of the Amazon, for example, the mere, an endangered species of fish, still lives.

    Authors: Nádia Pontes

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