Paleontologists say that the extinction of the dinosaurs may have led to the proliferation of rivers and dense forests, allowing mammals -- and eventually humans -- to thrive.
(CN) -- The extinction of the dinosaurs didn't just end a biological era, researchers think it also profoundly changed the environmental landscape -- waterways changed, forests grew lush and wide and eventually, mammals reigned supreme.
Evidence published Monday in the journal Communication Earth & Environment by scientists from the University of Michigan, the University of Alabama and the University of Florida show forests had an opportunity to flourish, expand and create a new ecosystem that impacted rivers.
The forests thrived after the Chicxulub asteroid impact and subsequent events killed nearly 75% of all living creatures on Earth, including all the dinosaurs except birds, in a era known as the Cretaceous-Paleogene, or K-Pg mass extinction, 66 million years ago.
"We know from the fossil record that forests rebounded in a matter of decades to centuries, and the geologic changes we see are far more consistent with a sudden increase in river-channel stability, not instability (which you would expect in an immediate post-extinction wasteland)," Luke Weaver, one of the authors of the study and an assistant professor in the UM Department of Earth and Environmental Science, said in an email.
By stabilizing sediments and moving water into rivers with wide meanders -- an S-shaped curve in a river's course -- Weaver said dense forests played an important role in how the natural world looked and worked after the dinosaurs.
The evidence was found in rock formations in Montana, North and South Dakota and Wyoming from the period shortly before and after the asteroid impact, with a small section of the geologic record showing an iridium anomaly, a fine layer of sediment loaded with the rare element. That layer -- brought by the asteroid, and spread widely and settled throughout the planet -- defines the K-Pg boundary.
"The geologic changes we highlight in this study represent a wholescale transformation in the way river borne sediments accumulated, and that change persisted for millions of years post-extinction," Weaver said. "None of that is consistent with the impact itself causing the change. And we contend that that abrupt change was caused by the extinction of dinosaur megafauna."
Weaver noted it was not necessarily the herbivore dinosaurs' voracious appetites that made forests during the Cretaceous period more spacious, but "more had to do with them trampling and uprooting vegetation that caused habitats to be more open and savannah-like and therefore did not constrain rivers," he said.
While studying rock layers in Montana, Weaver and co-authors Tom Tobin and Courtney Sprain first noticed the patterns in the Williston Basin in the northeastern region of the state. When they continued to find the same patterns in different parts of country, with different tectonic history, they concluded it to be "a universal phenomenon."
"We were not expecting this phenomenon to be so widespread," Weaver said. "Plenty of people had pet hypotheses for why the geology changed in certain areas, but none of those were sufficient, especially not to explain why you'd have such a stark change across such an enormous geographic area."
Ultimately, Weaver said, the new findings may give some idea of how climate change, habitat destruction and the biodiversity crisis may impact the Earth in our lifetimes -- a blink of an eye in geologic terms.
"The paper highlights how interconnected Earth's biosphere and geosphere are," he said. "Strong perturbations to one can have immense consequences for the other. And the K-Pg mass extinction is the closest analog we have to the severity and rapidity of human-induced changes to our planet."