MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
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PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: Diane Ainsworth
FOR IMMEDIATE RELEASEMarch 12, 1998
MORE EVIDENCE POINTS TO IMPACT AS DINOSAUR KILLER
Two new 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 230 kilometers (140 miles) from the rim of the
Chicxulub crater. This crater was formed when a 10-to-14-
kilometer diameter (6-to-8-mile) 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 200 kilometers (120 miles) 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 480 kilometers
(290 miles) 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 400 kilograms (900
pounds) 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 that 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.nasa.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.
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