Chixculub: changed the South American jungles (Introduction)

by David Turell , Thursday, April 01, 2021, 22:31 (1331 days ago) @ David Turell

More dense and covered by overhead canopy:

https://www.sciencenews.org/article/dinosaur-killing-asteroid-tropical-forest-fossil

"The day before a giant asteroid hit Earth 66 million years ago, a very different kind of rainforest thrived in what is now Colombia. Ferns unfurled and flowering shrubs bathed in the sunlight that streamed down through large gaps in the canopy between towering conifers.

"Then the bolide hit and everything changed. That impact not only set off a massive extinction event that wiped out more than 75 percent of life on Earth, but it also redefined Earth’s tropical rainforests, transforming them from sun-dappled, open-canopied forests into the dark, dense, lush, dripping forests of today’s Amazon, researchers report April 2 in Science.

"'A single historical accident changed the ecological and evolutionary trajectory of tropical rainforests,” says Carlos Jaramillo, a paleopalynologist — someone who studies ancient pollen — 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.”

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"The reasons why aren’t wholly clear. The region’s climate at the end of the Cretaceous Period 66 million years ago was similar to how it is today: hot and humid. But other factors were likely at work. Huge plant-eating sauropods, the long-necked dinosaurs, would have helped maintain the open gaps, letting light in, Jaramillo says (SN: 11/17/20). Once the asteroid hit, those dinosaurs were out of the picture. Extinction of certain plant families due to the impact also may have played a role, he says.

"A third likely factor was a shift in the chemical composition of the forest soil. Frequent rainfall during the warm, wet Cretaceous leached the soils of many nutrients, which would have favored gymnosperms like conifers, says Jaramillo. “The gymnosperms had this amazing ability to grow with very little food, and could outcompete the angiosperms.”

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"This is the first comprehensive picture of what happened in tropical ecosystems right after the extinction event, says paleoecologist Elena Stiles of the University of Washington in Seattle, who was not connected with the study. Most previous work on the chunks of time immediately before and after the extinction event — the very end of the Cretaceous and the start of the Paleogene Period — comes from North America, or from much farther south, such as in Patagonia, Stiles says (SN: 4/2/19). “In the tropics, there is no place where we have the boundary [between periods] preserved, [and] we have the limitation of a very fragmentary fossil record.'”

comment: Gerald Schroeder in his books about science and God wondered if God sent Chixculub. So do I.