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How the giant asteroid that wiped out dinosaurs emerged as a modern rainforest



Asteroid planet atmosphere

About 66 million years ago, a huge asteroid crashed into what is now the Yucatan Peninsula and plunged the earth into darkness. The impact changed the tropical rain forest and caused the domination of flowers.

Today̵

7;s tropical rainforest is a hot spot for biodiversity and plays an important role in the world’s climate system.A new study published today science Reveals the origin of modern tropical rainforests, and may help scientists understand how tropical rainforests will cope with the rapidly changing climate in the future.

This study led by researchers from the Smithsonian Tropical Research Institute (STRI) showed that the asteroid impact ended the dinosaur rule 66 million years ago and caused the extinction of 45% of the plants in Colombia today, which is a modern tropical rain forest. The domination of flowering plants.

Fern to flower

From forests full of ferns to forests full of flowers and plants: plants begin to produce attractive flowers, which contain sugary rewards for insects that carry pollen grains (basically the male sperm of the plant) to other flowers , Thereby helping plants to reproduce. This strategy is so successful that flowering plants have taken over tropical forests and the entire world. Image courtesy: Hace Tiempo. Columbia University of Columbia. The Alexander von Humboldt Institute of Tropical Sciences and the Smithsonian Institution. Alexander von Humboldt Institute (Imágenes) (BIA).

Mónica Carvalho, the first author and postdoctoral co-researcher of STRI and the University of Rosario in Colombia, said: “We want to know how tropical rain forests will change after severe ecological disturbances (such as the Chicxulub impact), so we are looking for tropical plant fossils.” “We The team checked more than 50,000 fossil pollen records and more than 6,000 leaf fossils before and after the impact.”

Colombia has been covered by forests for 125 to 100 million years

Between 125 and 100 million years ago, during the reign of the dinosaurs, most of Colombia today was covered by forests dominated by conifers and ferns. Image courtesy: Hace Tiempo. Columbia Columbia University. The Alexander von Humboldt Institute of Tropical Sciences and the Smithsonian Institution. Alexander von Humboldt Institute (Imágenes) (BIA).

In Central and South America, geologists are busy searching for fossils that have been cut by roads and exposed by landmines, which are washed away by heavy rains, and the jungles hide them. Prior to this study, little was known about the effects of this extinction on the evolution of flowering plants that currently dominate the tropical Americas.

STRI paleontologist Carlos Jaramillo and his team (mainly from many STRI researchers in Colombia) studied pollen grains in 39 locations, including rock outcrops and cores for oil exploration in Colombia, to paint a large area picture of the previous forest . And subsequent effects. Pollen and spores obtained from rocks older than impact indicate that rain forests are also dominated by ferns and flowering plants. Coniferous trees are common, such as the Kauri pine trees sold in supermarkets (Araucaria family) at Christmas and relatives of Norfolk Island pine trees. After the impact, the conifers almost completely disappeared from the tropical regions of the New World, and the flowering plants took over. After being affected, the plant diversity has not recovered for about 10 million years.

Plants after asteroid impact

After the asteroid impact in Mexico, almost half of the plants existed before the impact disappeared. After the shock, flowering plants began to dominate modern tropical forests. Image source: Hace Tiempo Columbia University, Columbia. Alexander von Humboldt Institute and Tropical Smithsonian Institution. Alexander von Humboldt Institute (Imágenes) (BIA).

The leaf fossils told the team a lot about the past climate and local environment. Carvalho and Fabiany Herrera, postdoctoral researchers at the Negaunee Institute for Conservation Science and Action at the Chicago Botanic Garden, led the study of more than 6,000 specimens. The research team worked with Scott Wing and others at the Smithsonian’s National Museum of Natural History and found evidence that the tropical trees before the impact were so far apart that light could reach the forest floor. Within 10 million years after the impact, some tropical forests were dense, just like today’s forests. The leaves of trees and vines left deep shadows on the small trees, shrubs and herbs below. The sparse canopy of the forest before the impact has fewer flowering plants, and less soil moisture migrates into the soil compared to the soil that has grown for millions of years.

“It’s like in the rain Cretaceous, But the way the forest works is different. “Carvalho said.

Paleocene in Bogotá

Modern Bogotá is an Andean city with an altitude of about 3000m (9000ft). But during the Paleocene (10 million years after the asteroid impact), it was covered by tropical forests. Insect damage to fossil leaves collected near Bogotá tells researchers that after the impact, insects of picky eaters (eating only certain species of insects) became less common and replaced by insects with a wider taste, which they could eat Many different plants are dropped. Image courtesy: Hace Tiempo. Columbia Columbia University. The Alexander von Humboldt Institute of Tropical Sciences and the Smithsonian Institution. The Imágenes Bank (BIA) of the Istituto Alexander von Humboldt Institute.

Before the extinction event, the research team found no signs of legumes, but after that, the leaves and pods of legumes have become very diverse and rich. Nowadays, legumes have become the main family in the tropical rainforest, and through the combination with bacteria, they absorb nitrogen from the air and convert it into soil fertilizer. The rise of pulses will greatly affect the nitrogen cycle.

Carvalho also collaborated with Conrad Labandeira of the Smithsonian’s National Museum of Natural History to study the destruction of leaf fossils by insects.

Flowering plants begin to diversify

From 66 to 100 million years ago, flowering plants began to diversify in the sea-level swamps and lowland forests where the Andes Mountains are now. Credit: A long time ago. A paleontological journey through Colombia. Alexander von Humboldt Institute and Smithsonian Tropical Institute. Picture Library (BIA), Alexander von Humboldt Institute.

Labandala said: “Insect damage to plants can be revealed in the miniature of a single leaf or the vast area of ​​a plant community. This is the basis of the vegetative structure of tropical forests.” “The energy that exists in plant tissues throughout the food chain. Eventually it will be passed on to pythons, eagles and jaguars. Its energy starts from insects, which are skeletonized through plant tissues, chewed, pierced and sucked, mined, rubbed and drilled. This evidence of the consumption food chain begins with insects All the diverse, dense and fascinating ways of consuming plants.”

“Before being affected, we found that different types of plants were damaged differently: eating was directed at the host,” Carvalho said. “After the impact, we found the same type of damage to almost every plant, which means eating more general.”

Fossil Euphorbia Leaf

Fossils from the leaves used in this study. A large leaf of insect breeding from the neotropical rainforest of the 58-60 Mayr, Bogotá Group, Colombia. Nowadays, Euphorbiaceae is one of the families with the largest number and most species in the lowland tropical rainforest. Image credit: Monica Carvalho.

How did the after-effects of the impact transform the sparse, conifer-rich tropical forest of the dinosaur era into the rainforest of today — towering trees dotted with yellow, purple, and pink flowers, and dotted with orchids? Based on evidence from pollen and leaves, the research team proposed three explanations for this change, all of which are correct. One idea is that the dinosaurs kept the forest open before the impact by eating and walking through the landscape. The second explanation is that the fly ash from the impact increases the soil throughout the tropics, providing an advantage for faster-growing flowering plants. The third explanation is that the preferential extinction of coniferous species creates an opportunity for flowering plants to take over the tropics.

“Our research follows a simple question: How does the tropical rain forest evolve?” Carvalho said. “The lesson learned is that, geographically speaking, tropical ecosystems will not only rebound under rapid turbulence, but vice versa. They were replaced, and the whole process took a long time.”

References: Mónica R. Carvalho, Carlos Jaramillo, Felipe de la Parra, Dayenari Caballero-Rodríguez, Fabiany Herrera, Scott Wing, Benjamin L. Turner, Carlos D’, “Extinction at the End of the Cretaceous Period and the Origin of the Modern Neotropical Rainforest” Apolli Tor, Miller, Randi Romero Baez, Paula Narvaz, Camilla Martinez, Mauricio Gutierrez, Conrad Labandra , Bayonne, Germany, Milton Rueda, Manuel Pez Ries, Dairon Cardinas, Alvaro Duke, James Crowley, Carlos Santos And Daniel Silvestro in 2021, science.
DOI: 10.1126/science.abf1969

The authors of this article are affiliated with STRI in Colombia, University of Rosario in Bogotá, Panama; University of Montpellier, France, CNRS, EPHE, IRD; University of Salamanca, Spain; Colombian Institute of Non-Petrochemical Research in Bucaramanga, Colombia; Chicago Botanic Garden; National Museum of Natural History in Washington, DC; University of Florida, We; Mato Grosso Federal University in Cuiabá, Brazil; Exxon Mobil Corporation, Texas Springs, USA; Technical Science Center-CONICET, Mendoza, Argentina; University of Santiago, Chile; University of Maryland College Park; Capital Normal University, Beijing, China; Geológica Ares, Bogota, Colombia; Paleoflora Ltda, Zapatoca, Colombia. University of Houston, Texas, USA; The Amazonian Institute of Science, Columbia Institute of Science, Leticia, Columbia; Columbia National University, Medellin, Columbia; Boise State University, Boise, Idaho, USA; BP Exploration Ltd., UK ; University of Fribourg in Switzerland.




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