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The impact of an asteroid that killed the dinosaurs gave rise to our planet’s rainforests, a study suggests.
The asteroid impact 66 million years ago led not only to the extinction of dinosaurs, but other forms of life.
Photo: 123RF
The researchers used fossil pollen and leaves from Colombia to investigate how the impact changed the tropical forests of South America.
After the 12 km wide space rock struck Earth 66 million years ago, the type of vegetation that made up these forests changed dramatically.
The team has described their findings in the prestigious journal Science.
Co-author Dr. Monica Carvalho, from the Smithsonian Institution for Tropical Research in Panama, said: “Our team examined more than 50,000 fossil pollen records and more than 6,000 leaf fossils before and after impact.”
They found that coniferous plants called conifers and ferns were common before the massive asteroid struck what is now Mexico’s Yucatan Peninsula.
But after the devastating impact, plant diversity was reduced by about 45 percent and extinctions became widespread, particularly among seed plants.
While forests recovered over the next 6 million years, angiosperms, or flowering plants, came to dominate them.
Modern rainforests are dense with thick canopies, unlike those of the late Cretaceous period.
Photo: 123RF
The structure of tropical forests also changed as a result of this transition. During the late Cretaceous period, when the dinosaurs were still alive, the trees that made up the forests were widely spaced. The tops did not overlap, leaving open sunlit areas on the forest floor.
But after the impact, the forests developed a dense canopy that allowed much less light to reach the ground.
So how did the impact transform the sparse coniferous-rich rainforests of the age of dinosaurs into the rainforests of today, with their towering trees dotted with flowers and multi-colored orchids?
From their analysis of the pollen and the leaves, the researchers propose three different explanations.
First, the dinosaurs could have prevented the forest from growing too dense by feeding on and trampling on the plants that grow in the lower levels of the forest.
A second explanation is that the ashfall from the impact enriched the soils of the tropics, giving faster-growing flowering plants an advantage.
The third explanation is that the preferential extinction of coniferous species created an opportunity for flowering plants to take over.
These ideas, the team says, are not mutually exclusive and all could have contributed to the outcome we see today.
“The lesson learned here is that under rapid disturbances … tropical ecosystems not only recover, they are replaced and the process takes a long time,” said Dr. Carvalho.
– BBC
