Meteorite That Doomed The Dinosaurs Also Remade Earth’s Forests

April Flowers for redOrbit.com – Your Universe Online
Approximately 66 million years ago, a relatively small chunk of rock changed the entire face of the planet. A meteorite, approximately 6 miles in diameter, impacted the Earth near the present-day site of the town of Chicxulub, in the Yucatan. With a force nearing that of 100 teratons of TNT, the meteorite left a crater nearly 100 miles wide and set off a megatsunami, wildfires, global earthquakes and volcanism that, to our knowledge, wiped out the dinosaurs and made way for the rise of mammals as the dominant species.
The question that hasn’t been answered until now is what happened to the plants. A new study led by the University of Arizona reveals that the same meteor strike that decimated the dinosaurs had the same effect on evergreen flowering plants, making way for the deciduous flowering plants. Their results, published in a recent journal of PLOS Biology, suggest that deciduous plants have properties that make them better able to rapidly respond to chaotically varying climate conditions.
The team used biomechanical formulae on thousands of fossilized leaves of angiosperms (flowering plants excluding conifers) to reconstruct the ecology of a diverse plant community that thrived during a 2.2 million year period. This time period spanned the impact event, which is believed to have killed off half the plant species of the time.
The evidence suggests that, for the most part, fast-growing, deciduous angiosperms replaced the slower-growing, evergreen plants after the event. Modern examples of evergreen angiosperms — for example, holly and ivy, are dark-leaved, slow-growing plants.

Image Above: This post-extinction landscape is lush from warm weather and ample rain along the Front Range, but there are only a few types of trees. Extinct relatives of sycamores, walnut trees, and palm trees are the most common. Credit: Donna Braginetz/courtesy of Denver Museum of Nature & Science
“When you look at forests around the world today, you don’t see many forests dominated by evergreen flowering plants,” said Benjamin Blonder, who graduated last year from the lab of UA Professor Brian Enquist with a Ph.D. from the UA’s Department of Ecology and Evolutionary Biology and is now the science coordinator at the UA SkySchool. “Instead, they are dominated by deciduous species, plants that lose their leaves at some point during the year.”
According to Blonder, the results provide much needed evidence of how the extinction level event affected plant communities. Before this study, scientists knew that plant species existed before the impact that were decidedly different from those existing after. What wasn’t understood, however, was whether the shift in plant assemblages was coincidental, or a direct result of the event.
“If you think about a mass extinction caused by catastrophic event such as a meteorite impacting Earth, you might imagine all species are equally likely to die,” Blonder said. “Survival of the fittest doesn’t apply — the impact is like a reset button. The alternative hypothesis, however, is that some species had properties that enabled them to survive.”
“Our study provides evidence of a dramatic shift from slow-growing plants to fast-growing species,” he said. “This tells us that the extinction was not random, and the way in which a plant acquires resources predicts how it can respond to a major disturbance. And potentially this also tells us why we find that modern forests are generally deciduous and not evergreen.”
Previous studies found evidence of an “impact winter,” or a temperature shift so dramatic that it caused plants to struggle in order to harvest enough sunlight to maintain metabolism and growth.
“The hypothesis is that the impact winter introduced a very variable climate,” Blonder said. “That would have favored plants that grew quickly and could take advantage of changing conditions, such as deciduous plants.”

Image Above: Seen here is a Late Cretaceous specimen from the Hell Creek Formation, morphotype HC62, taxon “Rhamnus” cleburni. Specimens are housed at the Denver Museum of Nature and Science in Denver, Colorado. Credit: Benjamin Blonder
The team – which included scientists from Wesleyan University, the Smithsonian National Museum of Natural History and the Denver Museum of Nature and Science – examined nearly 1,000 fossilized plant leaves collected from North Dakota. The samples were found embedded in rock layers known as the Hell Creek Formation and are currently housed at the Denver Museum of Nature and Science.
Analyzing the leaves was a new approach for predicting how plant species used carbon and water in the ancient world. This technique shed light on the ecological strategies of plant communities of long ago.
“We measured the mass of a given leaf in relation to its area, which tells us whether the leaf was a chunky, expensive one to make for the plant, or whether it was a more flimsy, cheap one,” Blonder explained. “In other words, how much carbon the plant had invested in the leaf.”
“There is a spectrum between fast- and slow-growing species,” said Blonder. “There is the ‘live fast, die young’ strategy and there is the ‘slow but steady’ strategy. You could compare it to financial strategies investing in stocks versus bonds.” The team’s results revealed that while slow-growing evergreens dominated the plant assemblages before the extinction event, fast-growing flowering species had taken their places afterward.
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