Amazon Rainforest Origin: Did the Asteroid That Caused Dinosaur Extinction Started It?

Forest vegetation in South America changed drastically, giving rise to today's Amazon rainforests after an asteroid hit the area. Said asteroid impact also led to the extinction of the dinosaurs 66 million years ago, a study published on Science and entitled "Extinction at the end-Cretaceous and the origin of modern Neotropical rainforests," revealed.

Researchers retrieved fossil leaves and pollen in Colombia to find out how the 12 kilometer-wide space rock that hit Earth altered the forests.

Carlos Jaramillo, a paleobiologist at the Smithsonian Tropical Research Institute in Panama and co-lead author of the study, indicated in a Scientific American feature that trees were not preserved in the fossil record, so his team turned to the fossil of leaves and pollen for new insights. Pollen, he stressed, is well preserved over time and quite common in fossil records. Its species is also varied morphologically, helping researchers ascertain the types of plants that existed in the ancient era.

Impact Causes Amazon Plant Diversity to Drop 45 Percent

In its findings, they discovered that cone-bearing plants named conifers and ferns were widespread before in the impact zone, which is now the Yucatan Peninsula in Mexico. After the asteroid struck, plant diversity dropped by about 45 percent as extinctions were prevalent, especially among the seed-bearing plants.

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In the next six million years, these forests recovered with the flowering plants, or angiosperms, now taking over the area.

(Photo: Lucian Dachman on Unsplash)

The tropical forests' structure also underwent a huge transformation. In the late Cretaceous Period, during the age of the dinosaurs, forest trees were widely spaced. There was no overlapping in the top parts, thus allowing open sunlit areas in the forest floor.

After the asteroid struck, a thick canopy grew in the forests that prevented sunlight from reaching the ground.

How did the impact change the dinosaur-age tropical rainforests into what they are today-all with the towering trees highlighted by multi-colored orchids and blossoms?

Explanations for Rainforest Transformation After Asteroid Impact

The study gave three explanations.

First, the dinosaurs themselves would have fed on and trampled the plants in the lower levels, preventing the forest from growing too dense.

Second, falling ash from the impact might have enriched the soils throughout the rainforest, and this would definitely prove beneficial to faster-growing flowering plants.

And lastly, the conifer species' preferential extinction led to a takeover by the flowering plants.

Researchers said the ideas are not mutually exclusive, and all these might have led to the rainforests we see at present.

Fundamental Advance in Knowledge

Pennsylvania State University geoscientist Peter Wilf, who is not involved in the study, underscored the significance of the research, which he said was "a fundamental advance in knowledge."

In a Scientific American feature, Wilf said: "The authors demonstrate that the dinosaur extinction was also a massive reset event for neotropical ecosystems, putting their evolution on an entirely new path leading directly to the extraordinary, diverse, spectacular and gravely threatened rain forests in the region today."

He added that the new insights would "provide new impetus for the conservation of the living evolutionary heritage in the tropics that supports human life, along with millions of living species."