Those silly scientists, just can't be trusted to know much about anything...<quoted text>
And here those silly scientists thought it was that little old asteroid that hit off the Yucatan Peninsula.
A new study says the asteroid that struck Earth 65 million years ago and wiped out the dinosaurs was particularly deadly to North America because it hit the Yucatan peninsula from the southeast at a 20- to 30-degree angle, spreading the devastating impact of its energy northwest.
The oblique angle of the asteroid's contact with Earth coupled its impact energy with that of the atmosphere and planetary surface to send waves of ground-hugging, vaporous fireballs onward, the study says. This resulted in an extinction intensity most severe downrange of the impact in North America.
...The researchers suggest that the relatively low angle of the Yucatan impact propelled a ballistic fireball downrange into North America. The fireball carried a two-mile-deep layer of vaporized rock and other material sheared off the Yucatan. The killing zone of matter cascaded through the atmosphere at near orbital speed, across North America and eventually around the globe.
"It was like a nuclear explosion taken north on a jet-powered sleigh ride," Schultz said. "This was indeed the day the Earth shook."
As evidence, the researchers show that the horseshoe-shaped Yucatan crater matches the structure of craters on the moon and Venus that were created when objects struck those heavenly bodies at oblique angles.
...The researchers said that biological evidence appears to support their oblique-impact hypothesis. North America, the first region to experience the fireball, had the most severe extinctions of plants.
After the devastation, ferns dominated the flora of central North America. Ferns accounted for 70 to 100 percent of the spore- or pollen-producing plants in the region after the impact, compared with only 10 to 40 percent before it. At the base of the food chain, plants are considered sensitive indicators of environmental devastation. Because ferns reproduce through the use of hardy spores, the plants are regarded as key flora in colonizing the site of a natural disaster.
Plants in parts of the world not downrange from the impact took a lesser hit from the corridor of incineration. For example, several ancient evergreen trees found in North America before the impact, but not after, still grow in parts of Australia and South America. Modern relatives of these trees, often called "primitive conifers," include the Norfolk Island pine, Chilean monkey puzzle and Wollemi pine.