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(meteorobs) More Evidence Points to Impact as Dinosaur Killer
>Date: Thu, 12 Mar 1998 11:33:19 -0500 (EST)
>From: NASANews@hq.nasadot gov
>Subject: More Evidence Points to Impact as Dinosaur Killer
>Sender: owner-press-release@lists.hq.nasadot gov
>To: undisclosed-recipients:;
>
>Douglas Isbell
>Headquarters, Washington, DC March 12, 1998
>(Phone: 202/358-1547)
>
>Diane Ainsworth
>Jet Propulsion Laboratory, Pasadena, CA
>(Phone: 818/354-5011)
>
>RELEASE: 98-42
>
>MORE EVIDENCE POINTS TO IMPACT AS DINOSAUR KILLER
>
> Two new impact crater sites in Belize and Mexico add further
>evidence to the hypothesis that an asteroid or comet collided with
>Earth about 65 million years ago, subsequently killing off the
>dinosaurs and many other species on the planet.
>
> Researchers Adriana Ocampo of NASA's Jet Propulsion
>Laboratory (JPL), Pasadena, CA, and Kevin Pope of Geo Eco Arc
>Research, La Canada-Flintridge, CA, led an international team that
>discovered the two new sites during a recent expedition sponsored
>by NASA's Exobiology Program and The Planetary Society, Pasadena, CA.
>
> "We discovered an important new site in Alvaro Obregon,
>Mexico, about 140 miles (230 kilometers) from the rim of the
>Chicxulub crater. This crater was formed when a 6-to-8-mile
>diameter (10-to-14-kilometer diameter) asteroid or comet collided
>with Earth," Ocampo said.
>
> "The site contains two layers of material, or ejecta, thrown
>out by the impact that flowed across the surface like a thick
>fluid, known as fluidized ejecta lobes," added Pope. "This is the
>closest surface exposure of ejecta to the Chicxulub crater that
>has yet been found and the best example known on Earth from a
>really big impact crater."
>
> Centered on the coast of Yucatan, Mexico, the Chicxulub
>crater is estimated to be about 120 miles (200 kilometers) in
>diameter. The impact 65 million years ago kicked up a global
>cloud of dust and sulfur gases that blocked sunlight from
>penetrating through the atmosphere and sent Earth into a decade of
>near-freezing temperatures. The drop in temperature and related
>environmental effects are thought to have brought about the demise
>of the dinosaurs and about 75 percent of the other species on Earth.
>
> The Earth orbits the Sun in a swarm of so-called near-Earth
>objects, whether they are comets or asteroids, yet the science of
>detecting and tracking them is still relatively young. Only a
>handful of astronomers around the world search for these objects,
>and they estimate that currently only about one-tenth of the
>population of near-Earth objects has been detected. Chicxulub is
>the only impact event that has been correlated with mass
>extinctions to date. The site has been dated geologically to the
>boundary between the Cretaceous and Tertiary periods, also known
>as the K/T boundary.
>
> Local geologist Brian Holland of Punta Gorda, Belize, guided
>the expedition to another new ejecta site about 290 miles (480
>kilometers) from the crater rim. This Belize site contains tiny
>spheres of altered green glass, called tektites. Tektites are
>rocks that have been melted to glass by the severe heat of an
>impact. Expedition member Jan Smit of Free University, Amsterdam,
>noted that the Belize tektites were similar to those found in
>Haiti and northern Mexico. This finding links the stratigraphy of
>the Belize sites to the more distant Caribbean and Mexican ejecta sites.
>
> Alfred Fischer of the University of Southern California,
>Michael Gibson of the University of Tennessee at Martin, and Jaime
>Urrutia and Francisco Vega of the National Autonomous University
>of Mexico helped the team collect 900 pounds (400 kilograms) of
>samples, including drill cores, for paleomagnetic studies. They
>also collected fossils from the site to help date the deposits and
>add new pieces to the puzzle of what happened at Chicxulub 65
>million years ago.
>
> Impact ejecta is very rare on Earth, but covers much of the
>surface of Mars because Mars' surface has remained stable and
>unchanged for billions of years, thus preserving debris from these
>rare impact events. Also, such fluidized ejecta lobes have never
>been observed directly on Earth before and can serve as an
>excellent laboratory for studying the ejecta lobes surrounding
>many Martian craters.
>
> "The discovery of these new ejecta sites is very exciting,"
>said team co-leader Ocampo. "It is like seeing a bit of Mars on Earth."
>
> The exact nature of these ejecta lobes on Mars remains a
>mystery, Ocampo noted. Some scientists think they were created by
>an abundance of water in the Martian crust, which turned the
>ejecta into a muddy, molasses-like material. Others suggest the
>fluidized ejecta lobes were enabled by a much thicker atmosphere
>in Mars' early history. As flying ejecta from an impact event flew
>through the Martian atmosphere, it was reduced by friction to a
>very dense, turbulent cloud of debris, which also flowed like
>water. Study of the Chicxulub fluidized ejecta may help settle
>this debate and shed new light on theories that the Martian
>surface may once have been more hospitable for life.
>
> Volunteers who assisted The Planetary Society and the
>scientists in the field have posted their photographs of the
>expedition on The Planetary Society web site at the following URL:
>
> http://planetary.org
>
> Information about and images of newly discovered near-Earth
>objects found by JPL's ongoing Near-Earth Asteroid Tracking (NEAT)
>program are available at:
>
> http://huey.jpl.nasadot gov/~spravdo/neat.html
>
> Ocampo and Pope's research was funded in part by the
>Exobiology Program of NASA's Office of Space Science, Washington,
>DC. NASA's Jet Propulsion Laboratory is a division of the
>California Institute of Technology, Pasadena, CA.
>
> -end-
>
>
>
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