[meteorite-list] Research Yields Greater Precision in Determining Age of Meteorites

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 22 Jul 2010 11:33:02 -0700 (PDT)
Message-ID: <201007221833.o6MIX2kt010112_at_zagami.jpl.nasa.gov>

NEWS RELEASE FROM THE PLANETARY SCIENCE INSTITUTE

SENT:
July 21, 2010

FROM:
Alan Fischer
Public Information Office
Planetary Science Institute
520-885-5648
fischer at psi.edu

 
Research Yields Greater Precision in Determining Age of Meteorites

Researchers have aged dated a very important group of meteorites with
far greater precision than previously possible by using a different type
of radioactive dating on a particularly difficult type of specimen to study.

The project found that the asteroid from which ureilite meteorites are
derived differentiated - or separated into parts of different
composition - within 5 million years of the formation of the Solar
System, said Cyrena Anne Goodrich, senior scientist at the Planetary
Science Institute. "That is a really short time period," she said.

Goodrich's research offered dating with approximately 10 times greater
precision than previously available.

Most meteorite dating research has looked at two types of meteorite -
angrites and eucrites - which contain ample amounts of minerals
necessary for the study. Goodrich and her team opted to investigate
ureilites.

The project's radioactive isotope dating methods looked at short-lived
radionuclides rather than the long-lived radionuclides that researchers
have studied for years.

"Ureilites are the second most abundant group of differentiated
meteorites, but they are particularly enigmatic and are very difficult
to date because they don't contain many different minerals," she said.

Radiometric dating is based on the principle that radioactive elements
decay and change into other elements at a constant rate that can be
measured in a laboratory. The basic idea behind radioactive dating is
that if you can measure the ratio of parent to daughter isotopes in a
rock or mineral using a mass spectrometer, which separates isotopes from
one another according to their weight, you can calculate its age.

"Short-lived radionuclides are isotopes that decay much faster than the
long-lived ones. In fact, they decay so quickly that any parent atoms
that were present at the time the Solar System formed would have
completely changed into daughter isotopes a long time ago," she said.
"By measuring the daughter isotopes in several different minerals, it is
possible to determine how much of the parent isotope was in the rock
when rock formed, and this value can be compared to a known value for
how much of the parent was present at some specific time, say at the
formation of the Solar System."

Goodrich's research, which was funded by NASA grants, studied how
isotopes manganese-53 decays to chromium-53 and aluminum-26 decays to
magnesium 26. "We were able to apply Mn-Cr and Al-Mg dating to ureilites
because I discovered some unusual Mn-rich and Al-rich minerals in a
couple of rare types of ureilites," she said. "The results of our work
provide the first high-precision ages dates for ureilites, 4.5639
billion years ago, plus or minus 0.00045 billion years (450,000 years)."

Earlier dating efforts for ureilites offered precision of only plus or
minus 6 million years, she said.

"The beauty of this technique is that it has much smaller uncertainties
than the long-lived radionuclide dating technique, and the development
of this method has resulted in scientists using meteorites to work out
many details of what happened in our Solar System in the first 5-6
million years of its history. In particular, they have been able to
reconstruct many details of the early differentiation of planetesimals
like asteroids."

Goodrich is lead author of a paper, "53Mn-53Cr and 26Al-26Mg ages of a
feldspathic lithology in polymict ureilites," appearing in Earth &
Planetary Science Letters in July.

Meteorites are a solid piece of some planetary body - planets, moons,
asteroids and comets in our Solar System - other than Earth that got
chipped off its "parent body" and made its way to Earth. Meteorites are
"free samples" of other bodies, and the vast majority of the world's
collections totaling more than 39,000 specimens come from various asteroids.

Meteorites are an invaluable source of information about the formation
and early evolution of our Solar System, partly because any record of
the Earth's earliest history has been destroyed by subsequent geological
processing. Without meteorites we would probably know very little about
the beginnings of our Solar System, Goodrich said.

CONTACT:

Cyrena Anne Goodrich
Senior Scientist
802-875-1509
cgoodrich at psi.edu
Received on Thu 22 Jul 2010 02:33:02 PM PDT