- Global wildfires ignited by high-velocity debris from
the catastrophic impact of an asteroid or comet with Earth 65 million years
ago spread over southern North America, the Indian subcontinent and most
of the equatorial part of the world one to three days after impact, according
to a new study.
-
- But northern Asia, Europe, Antarctica and possibly much
of Australia may have been spared, David A. Kring of the University of
Arizona and Daniel D. Durda of the Southwest Research Institute report
in the Journal of Geophysical Research -- Planets.
-
- UA planetary scientist H. Jay Melosh in 1990 and others
modeled global wildfire scenarios from the horrific impact that is thought
to have led to one of the greatest mass extinctions in Earth history, including
dinosaur extinction. The impact that blasted the immense Chicxulub crater
near Yucatan, Mexico, marked the end of the Age of Reptiles, the Mesozoic,
and heralded the Age of Mammals, the Cenozoic.
-
- "We've added more detail in re-evaluating the extent
of the wildfires," Kring said. "Our new calculations show that
the fires were not ignited in a single pulse, but in multiple pulses at
different times around the world. We also explored how the trajectory of
the impacting object, which is still unknown, may affect the distribution
of these fires."
-
- Their more detailed modeling suggests pulses of misery
for life on Earth during days after impact. More than 75 percent of the
planet's plant and animal species did not survive to see the Cenozoic.
-
- "The fires were generated after debris ejected from
the crater was lofted far above the Earth's atmosphere and then rained
back down over a period of about four days. Like countless trillions of
meteors, the debris heated the atmosphere and surface temperatures so intensely
that ground vegetation spontaneously ignited."
-
- The collision was so energetic -- 10 billion times more
energetic than the nuclear bombs that flattened Hiroshima and Nagasaki
in 1945 -- that 12 percent of the impact debris was launched beyond Earth
into the solar system, Kring said.
-
- About 25 percent of the debris rained back through the
atmosphere within two hours of impact. Fifty-five percent fell back to
Earth within 8 hours of impact, and 85 percent showered down within 72
hours of impact, according to Kring's and Durda's calculations.
-
- Both physics and Earth's rotation determined the global
wildfire pattern. High-energy debris would have concentrated both around
the Chicxulub crater in Mexico and its global antipode -- which corresponded
to India and the Indian Ocean 65 million years ago. "The way to think
of this is, the material was launched around Earth and headed on a return
trajectory to its launch point," he explained.
-
- "Then, because the Earth rotates, it turned beneath
this returning plume of debris, and the fires migrated to the west. That's
what causes the wildfire pattern."
-
- Durda has turned the simulations into a movie that can
be viewed at the Lunar and Planetary Lab Space Imagery Center Web site,
http://www.lpl.Arizona.edu/SIC/news/chicxulub2.html
-
- Kring and Durda noted not in this paper, but in an unrefereed
abstract, that post-impact wildfires generated as much carbon dioxide,
and perhaps more carbon dioxide, than limestone vaporized at the impact
site. Wildfires played at least as big a role as the limestone target site
in disrupting the carbon cycle and in greenhouse warming.
-
- The team proposes to model other impact events using
the code they developed for these simulations.
-
-
- Note: This story has been adapted from a news release
issued by University Of Arizona for journalists and other members of the
public. If you wish to quote from any part of this story, please credit
University Of Arizona as the original source. You may also wish to include
the following link in any citation:
-
- http://www.sciencedaily.com/releases/2002/09/020910081734.htm
-
- Copyright © 1995-2002 ScienceDaily Magazine
|
