Quirks and Quarks

The asteroid that wiped out the dinosaurs might have created the rainforests

The tropical rainforests we see today in South America might not have flourished had it not been for the asteroid that struck Earth 66 million years ago.

As with animals, the catastrophe wiped the slate clean and allowed different organisms to take over

Fossil leaves like this one from a field site near Bogota indicate the type of forests that existed before and after an asteroid hit the Earth 66 million years ago. (Carlos Jaramillo)

The asteroid impact 66 million years ago that ended the Cretaceous period transformed life on our planet. The dinosaurs were among 75 per cent of all life that went extinct.

Conifers and ferns had dominated the landscape in the tropics up to that point, but a new lineage of angiosperms — flowering plants — was developing. When the dust from the impact had literally settled, the flowering plants had an opportunity to establish themselves on a blank canvas.

According to a new study by Carlos Jaramillo and his colleagues, the result, after several million years of evolution, was the dense, diverse tropical rainforests we know today. Jaramillo is a geologist and paleontologist from the Smithsonian Tropical Research Institute in Panama and the University of Salamanca in Spain.

Pollen and leaf fossils

Jaramillo and his team studied fossil pollen and fossil leaves ranging in age from 72 million to 58 million years ago from sites in Central and South America. These fossils indicated a dramatic drop in plant diversity at 66 million years, when the asteroid devastated life on Earth.

Fossil pollen, like this one from the Buttinia genus, found in rocks indicate plant diversity on either side of the asteroid impact 66 million years ago (Carlos Jaramillo)

The fossils also confirmed that tropical forests before the impact had been dominated by conifers that were part of an open canopy forest of widely spaced trees and open forest floor. Dinosaurs played a key role in maintaining this open landscape by continual trampling and eating vegetation, much like elephants do in present day Africa.

No asteroid, no rainforest

The forests prior to the impact also had low levels of nutrients. But the vast clouds of minerals ejected onto the landscape by the asteroid impact increased nutrient levels, particularly phosphorous. This paved the way for the angiosperm trees and plants that did survive the impact to flourish.

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Fossil leaf from the Paleocene, a plant that flourished after the asteroid impact. (Carlos Jaramillo)

They came to dominate and by seven million years after the asteroid impact closed canopy, dense rainforests with high levels of diversity were in place. 

How the rainforests came to be. Smithsonian Tropical Research Institute