Ancient Denvers by Kirk Johnson

Author:Kirk Johnson
Language: eng
Format: epub
Publisher: Chicago Review Press
Published: 2020-01-15T00:00:00+00:00

Excavation for Denver International Airport in 1991 exposed thousands of fossils.

A museum volunteer holds the base of a fossil palm frond.

In a flash, about 65.5 million years ago, an asteroid about the size of Denver struck Earth in the shallow seas that covered Mexico’s Yucatan Peninsula. This was the largest known extraterrestrial impact on Earth and the results were devastating all around the world. Dinosaurs and their ecosystems were literally blown away. North America, due to its proximity to ground zero, was hardest hit but forests on the other side of the world in New Zealand were also flattened and incinerated. It was a humongous disaster, yet there were survivors such as certain plants, small animals and birds, and aquatic creatures. These were the lonely colonists of the new ecosystems that formed in the years and millennia after the impact. The fact that Colorado had topography in the form of the Front Range was a good thing, as survivorship here was greater than it was farther north where there were no mountains to provide protection from the blast.

This was also a time of great volcanism in the Rockies. It was during this time that the minerals of the Colorado Mineral Belt were emplaced by the percolation of gold- and silver-laced hot water associated with volcanic activity. Lava eruptions near Golden flowed out across the landscape and remain today as the mesa-capping layers at the top of North and South Table Mountains. More distant volcanoes, behaving like Mount Saint Helens, repeatedly blasted volcanic ash into the sky, dusting the forests. An excellent example of this was discovered during the excavation for Concourse B at Denver International Airport in 1991. Workers found a coal seam, the remains of a 65 million-year-old palm and walnut swamp. The coal seam contained forty-seven distinct ash layers, showing that the swamp had been dusted by forty-seven eruptions.

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