Monday, March 7, 2016
Ian Miller, PhD, Curator of Paleobotany
Chair, Department of Earth Sciences
Director, Earth and Space Sciences
Deciduousness and The KT Extinction: How An Asteroid Shaped the Forest in Your Backyard.It has been long hypothesized that many deciduous trees that live in our backyard today, have ancestors that first evolved to shed their leaves in response to changing light conditions, as opposed to either changing temperature or moisture.
Ancestors of these trees can be traced back to the time of the dinosaurs, when the earth was, for the most part, a greenhouse.
As a result, both the North and South Poles would have been free of ice and completely covered by forests. Trees living near the North or South Pole would have flourished in a season of light, when they leafed out and grew as much as possible, and they would have ceased to grow through a season of darkness, when they adapted to lose their leaves and lay dormant.
Research at the Denver Museum of Nature & Science focused on the extinction of the dinosaurs in North Dakota and Montana and suggests that many plants also went extinct too. Caused by the impact of an asteroid 10 kilometers in diameter that hit the Yucatan Peninsula, the first minutes to hours of the extinction saw a massive shockwave, an intense fire storm, towering tsunamis, and an atmospheric thermal pulse equivalent to temperatures in an oven that would be hot enough to bake cookies. As these effects subsided, dust in the air persisted and blotted out much of the sun for months to even a year or two.
Many plants were in trouble, since they need abundant light to photosynthesize. However, those plants in the Polar Regions that had evolved to be deciduous were already adapted to a season of darkness, and, as a result, fared better.
Today many trees that lose their leaves in the fall, have ancestors that survived the darkness that followed the impact of the asteroid that killed the dinosaurs.