[meteorite-list] Study Finds that a Single Impact Killed the Dinosaurs

[Ron Baalke]

http://munews.missouri.edu/NewsBureauSingleNews.cfm?newsid=12264

University of Missouri-Columbia News Release
Contact: Katherine Kostiuk
Sr. Information Specialist
573-882-3346
KostiukK at missouri.edu 

Study Finds that a Single Impact Killed the Dinosaurs
Data supports the single-impact theory in a controversial discussion

November 28, 2006

COLUMBIA, Mo. - The dinosaurs, along with the majority of all other
animal species on Earth, went extinct approximately 65 million years
ago. Some scientists have said that the impact of a large meteorite in
the Yucatan Peninsula, in what is today Mexico, caused the mass
extinction, while others argue that there must have been additional
meteorite impacts or other stresses around the same time. A new study
provides compelling evidence that "one and only one impact" caused the
mass extinction, according to a University of Missouri-Columbia researcher.

"The samples we found strongly support the single impact hypothesis,"
said Ken MacLeod, associate professor of geological sciences at MU and
lead investigator of the study. "Our samples come from very complete,
expanded sections without deposits related to large, direct effects of
the impact - for example, landslides - that can shuffle the record, so
we can resolve the sequence of events well. What we see is a unique
layer composed of impact-related material precisely at the level of the
disappearance of many species of marine plankton that were
contemporaries of the youngest dinosaurs. We do not find any
sedimentological or geochemical evidence for additional impacts above or
below this level, as proposed in multiple impact scenarios."

MacLeod and his co-investigators studied sediment recovered from the
Demerara Rise in the Atlantic Ocean northeast of South America, about
4,500 km (approximately 2,800 miles) from the impact site on the Yucatan
Peninsula. Sites closer to and farther from the impact site have been
studied, but few intermediary sites such as this have been explored.
Interpretation of samples from locations close to the crater are
complicated by factors such as waves, earthquakes and landslides that
likely followed the impact and would have reworked the sediment. Samples
from farther away received little impact debris and often don't
demonstrably contain a complete record of the mass extinction interval.
The Demerara Rise samples, thus, provide an unusually clear picture of
the events at the time of the mass extinction.

"With our samples, there just aren't many complications to confuse
interpretation. You could say that you're looking at textbook quality
samples, and the textbook could be used for an introductory class,"
MacLeod said. "It's remarkable the degree to which our samples follow
predictions given a mass extinction caused by a single impact.
Sedimentological and paleontological complexities are minor, the right
aged-material is present, and there is no support for multiple impacts
or other stresses leading up to or following the deposition of material
from the impact."

The impact of a meteorite on the Yucatan Peninsula likely caused massive
earthquakes and tsunamis. Dust from the impact entered the atmosphere
and blocked sunlight, causing plants to die and animals to lose
important sources of food. Temperatures probably cooled significantly
around the globe before warming in the following centuries, wildfires on
an unprecedented scale may have burned and acid rain might have poured
down. MacLeod and many other scientists believe that these effects led
to the relatively rapid extinction of most species on the planet. Some
other scientists have argued that a single impact could not have caused
the changes observed and say that the impact in the Yucatan predates the
mass extinction by 300,000 years.

MacLeod's co-investigators were Donna L. Whitney from the University of
Minnesota, Brian T. Huber from the Smithsonian National Museum of
Natural History and Christian Koeberl of the University of Vienna. The
study was recently published in the 'in press' section of the online
version of the Geological Society of America Bulletin. Funding was
provided by the U.S. Science Support Program, the U.S. National Science
Foundation and the Austrian Science Foundation. Samples were recovered
on Leg 207 of the Ocean Drilling Program.

-30-