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How the Chicxulub impactor triggered the modern rainforest-ScienceDaily



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 reign of flowers.

Today’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.

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 look 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.”

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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 STRI researchers (many of whom are from Colombia), studied pollen grains at 39 locations, including rock outcrops and cores for oil exploration in Colombia, thus depicting Colombia’s large scale. Regional picture. The impact before and after the forest. Pollen and spores obtained from rocks older than impact indicate that rain forests are also dominated by ferns and flowering plants. Coniferous trees such as Kauri (relatives of Kauri pine and Norfolk Island pine) sold in supermarkets (Araucaria family) at Christmas are common and cast shadows on dinosaur footprints. 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.

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. In the ten 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.

“There were as many rainy days as the Cretaceous, but the way the forest worked was different.” Carvalho said.

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, leguminous plants have become the main family in tropical rain forests. 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.

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

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

How did the after-effects of the impact transform the sparse, conifer-rich tropical forest of the dinosaur era into the rainforest of today-tall trees dotted with yellow, purple, and pink flowers and 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 enriches the soil throughout the tropics, providing advantages 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 from here is that under fast turbulent conditions (from a geological point of view) tropical ecosystems will not only rebound, they will also be replaced, and this process will take a long time.”

The Smithsonian Tropical Research Institute is a subsidiary of the Smithsonian Institution and is headquartered in Panama City, Panama. The institute further understands tropical biodiversity and its importance to human well-being, trains students to conduct research in tropical areas, and promotes conservation by raising public awareness of the beauty and importance of tropical ecosystems.


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