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(meteorobs) Asteroid hits at deadly oblique angle...65 mil years ago(long article)
A friend sent me the following ...thought to share it with you all.
George Z.
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ASTEROID HIT AT DEADLY OBLIQUE ANGLE 65 MILLION YEARS AGO
From The Brown University News Bureau
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 study
suggests one rationale for the dire consequences of such an
impact--the severity of extinctions that result from an object's
impact on Earth may reflect the incoming object's angle.
"This finding may help us determine what other impacts did to
Earth in the past and what they may do in the future," said Peter
Schultz, professor of geological sciences at Brown University.
Schultz and Steven D'Hondt, professor of oceanography at the
University of Rhode Island, are co-authors of the study in the
November issue of the journal Geology.
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. Venus's thick atmosphere holds in place gases
emitted from a crater after an impact. The researchers studied
images of these corked-in Venusian vapors, which show that
gaseous material is propelled in waves downrange after an object
strikes a planetary surface at an oblique angle.
Schultz used a high-powered gun to recreate the dynamics of an
object striking Earth's surface at a 20- to 30-degree angle. The
experiment produced horseshoe-shaped craters, while high-speed
film captured gas and materials jettisoned downrange.
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.
"The basic point of the study is that we can determine the impact
angle of this object and that the angle matters," D'Hondt said.
Most scientists study the aftermath of collisions that caused
Earth's craters as if objects struck the planet at 90-degree
angles, or from directly overhead. But such vertical impacts are
very rare.
An oblique angle of impact may have more deadly global
consequences than a vertical impact, because an oblique impact
should release a greater fraction of impact energy to the
atmosphere and surface target, said Schultz and D'Hondt.
"The study also underscores the point that regional repercussions
can be expected from an Earth-object impact, something scientists
have rarely considered in previous studies of this 65-million-
year-old event," D'Hondt said.
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