Researchers using refined techniques
to study minerals from meteorites now believe it took about 20 million
years for the Earth to coalesce from the materials already gathered
around our sun as the solar system. Recent estimates had pegged the
interval closer to 50 million years.

Brigitte Zanda-Hewins, an adjunct member of the graduate faculty at
Rutgers department of geological sciences and associate professor at
the mineralogy laboratory of the Muséum National d’Histoire Naturelle
in Paris, is among a group of researchers publishing its findings in
the international journal "Science," on Mar. 1.

The group studied radioactive forms of the elements niobium and
zirconium found in samples of meteorites. Because meteorites are the
oldest objects of our solar system available for study, scientists
use their components as a kind of "radioactive chronometer" to help
estimate time intervals separating events during the formation of
the solar system, including the formation of the Earth.

While recent attempts to use the niobium-zirconium "chronometer" had
produced the 50-million-year estimate, Zanda-Hewins said the new
20-million-year figure is the result of performing mineral
separations in the samples for the first time, and using extreme
precautions to maintain the purity of the samples. Researchers used
special processing equipment, anti-contamination air flow and
filters, magnetic separation devices and a wide range of chemical
separation techniques to avoid any interference by foreign materials.

"We designed an extremely careful approach to separate the minerals
and isolate the right ones," she said. The method is described in
the article entitled "Niobium-Zirconium Chronometry and Early Solar
System Development."

Zanda-Hewins’ co-authors are Maria Schönbächler, Mark Rehkämper, Alex
N. Halliday and Der-Chuen Lee of ETH Zurich Institute of Isotope
Geology and Mineral Resources; Bodo Hattendorf and Detlef Günther
of ETH Zurich Laboratory of Inorganic Chemistry; and Michèle
Bourot-Denise of the Muséum National d’Histoire Naturelle in Paris.

Besides her work at Rutgers, Zanda-Hewins is well-known as a Paris-
based geologist who helps coordinate distribution of meteorite samples
for scientific study around the world. She is the author of the 2001
book "Meteorites: Their Impact on Science and History."