- An asteroid effect wiped out most life on the planet 66 million years ago.
- Before the asteroid, Colombian forests were airy and light with tall conifers.
- Scientists used plant and pollen fossils to trace the changes over millions of years.
The dense, dark rainforests of what is today Colombia looked very different 66 million years ago.
Sunlight streamed through tall conifers to reach ferns and flowering shrubs with plenty of room to grow along the forest floor. The air was much less humid. And yes, there were dinosaurs.
Then a giant asteroid slammed into the ground, wiping out 75% of life on the planet, ending the Cretaceous.
“A single historic accident changed the ecological and evolutionary trajectory of tropical rainforests,” Carlos Jaramillo of the Smithsonian Tropical Research Institute told the Panama City Science News. “The forests we have today are really the by-product of what happened 66 million years ago.”
Jaramillo is a paleopalynologist, which means he studies old pollen. He was part of a team that spent 20 years collecting and analyzing thousands of fossils of pollen, spores and leaves from 72 million to 58 million years ago. Their study was published last week in Science.
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“It took us a long time to gather enough data to get a clear picture of what went on during the extinction,” said Mónica Carvalho, lead author and postdoctoral fellow at the Smithsonian Tropical Research Institute, Ars Technica.
After the asteroid, almost half of the plant species in Colombia disappeared. The cone-bearing conifers died off. Over the next 6 million years, the remaining flowering plants and ferns took over the rainforest.
They grew close together, creating the thick canopy that blocked the sun. The water that evaporated from the leaves increased the humidity.
Researchers have some ideas as to why this change occurred.
Without hungry herbivorous dinosaurs penetrating the vegetation and going through the bushes, the plants can grow untouched. Conifers have simply no longer been suitable for the tropics.
Finally, remember the asteroid? It could have released tsunamis that deposited carbon-rich sediment in the forests. Ash from forest fires triggered by the explosion could have acted as fertilizer. Conifers do not do as well in nutrient-rich soils as flowering plants.
“This is something we continue to explore as we search for more fossil sites and as we continue to study the tropics,” Carvalho said.
Bonnie Jacobs, a paleobotanist at Southern Methodist University in Texas who was not part of the study, told New Scientist, “We love the way it ended, this incredibly diverse, truly structurally complex forest, but right now we are living through a mass extinction caused by humans and again entire ecosystems are put on a different path. In the case of the rainforest, we like the end product, but all the animals that lived in chalk did not. ”
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Jaramillo said the rainforest trail took over the millions of years, has lessons for us today as we see extensive deforestation in the Amazon and around the world.
“In some of the places we studied, I could see right before my eyes how this forest, which has taken 66 million years to build, was gone in a day, and the deforestation is astonishing,” Jaramillo told New Scientist. “We know from this study that it takes a long time to rebuild these diverse forests: You can not cut into the forest and think, ‘Oh, tomorrow I will plant more trees.’ ”
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