Space Forum / Space Science / September 2005

http://news.uns.purdue.edu/UNS/html4ever/2005/050927.Lipschutz.meteorites.htm

Meteorites offer glimpse of the early Earth, say Purdue scientists
Purdue University
September 27, 2005

WEST LAFAYETTE, Ind. - Important clues to the environment in which the
early Earth formed may be emerging from Purdue University scientists'
recent study of a particular class of meteorites.

By examining the chemistry of 29 chunks of rock that formed billions of
years ago, probably in close proximity to our planet, two Purdue
researchers, Michael E. Lipschutz and Ming-Sheng Wang, have clarified
our understanding of the conditions present in the vicinity of the
ancient Earth's orbit. Because direct evidence for these conditions is
lacking in terrestrial samples, the scientists believe that the
composition of these so-called enstatite chondrite (EC) meteorites
could
offer a window into the planet's distant past.

"What happened to these rocks most likely happened to the Earth in its
early stages - with one great exception," said Lipschutz, a professor
of
chemistry in Purdue's College of Science. "Shortly after the early
Earth
formed, an object the size of Mars smashed into it, and the heat from
the cataclysm irrevocably altered the geochemical makeup of our entire
planet. These EC meteorites, however, are likely formed of matter
similar to that which formed the early Earth, but they were not
involved
in this great collision and so were not chemically altered. They might
be the last remaining pristine bits of the material that became the
planet beneath our feet."

The research appears in today's (Sept. 27) edition of a new journal,
Environmental Chemistry, which solicited the paper. Lipschutz said the
journal's editorial board includes F. Sherwood Rowland and Mario
Molina,
who received the Nobel prize for their discovery that Earth's
protective
ozone layer was threatened by human activity.

Lipschutz and Wang initially set out to increase our knowledge of EC
meteorites, one of many different meteorite classes. Meteorites come
from many different parts of the solar system, and a scientist can link
one with its parent object by determining the different isotopes of
oxygen in a meteorite's minerals. Chunks of the moon, the Earth and EC
meteorites, for example, have very similar isotopic "signatures," quite
different from those of Mars and other objects formed in the asteroid
belt. The variations occurred because different materials condensed in
different regions of the disk of gas and dust that formed the sun and
planets.

Bits of these materials orbit the sun, occasionally falling to earth as
meteorites. But there is one place on our planet that meteorites
accumulate and are preserved in a pristine fashion - the ice sheet of
Antarctica.

"Over the millennia, many thousands of meteorites have struck the
Antarctic ice sheet, which both preserves them and slowly concentrates
them near mountains sticking through the ice, much as ocean waves wash
pebbles to the shore," said Lipschutz. "These stones have come from
many
different parts of the solar system and have given us a better picture
of the overall properties of their parent objects."

By examining their mineralogy, scientists have determined that about
200
of these Antarctic stones are EC meteorites that formed from the same
local batch of material as the Earth did more than 4.5 billion years
ago. But there is additional information that the chemistry of these
ECs
can offer on the temperatures at which they formed. To obtain this
information, however, required Lipschutz to analyze chemicals in the
meteorites called volatiles - rare elements such as indium, thallium
and
cadmium.

"Volatiles in meteorites can give unique information on their
temperature histories, but only 14 of them had ever been analyzed for
these elements," Lipschutz said. "Naturally, we want to know the story
behind the formation of objects in our own neighborhood, so we set out
to increase that number."

In this study, the researchers gathered samples taken from another 15
EC
meteorites that had, for the most part, landed in Antarctica tens of
thousands of years ago. Using a unique method involving bombardment of
the samples with neutrons, chemically separating the radioactive
species
and counting them, the researchers were able to determine the amounts
of
15 volatiles that together offered clues to each rock's heating
history.

"Volatiles can act like thermometers," Lipschutz said. "They can tell
you whether the temperature was high or low when the rock formed. We
tested two different kinds of ECs, and the oldest, most primitive
examples of each kind had very similar volatile contents - which means
their temperature at formation was similar. These rocks have
essentially
recorded the temperature at which the early Earth formed, and we now
know that this was much lower than 500 degrees Celsius."

The two different kinds of EC meteorites, known as ELs and EHs, were
found in the Purdue study to have condensed at low temperatures like
the
Earth. However, the two groups are controversial because scientists
have
not been able to agree on whether they originated from a single parent
object or two different ones. Unfortunately, Lipschutz said, the data
from the 29 ECs they analyzed were insufficient to settle the issue.

"There are still quite a few unanswered questions about the earliest
periods of the Earth's history, and this study only provides one piece
of the puzzle," he said. "But aspects of this study also show that ECs
differ substantially from other meteorite types that came from much
farther out in the disk, in the region of the asteroid belt."

For Lipschutz, who had an asteroid named for him on his 50th birthday
in
honor of his many studies of meteorites, their parent bodies and the
early history of the solar system, deeper answers may lie farther away
than Antarctica.

"If we understand how our solar system formed, we might be better able
to understand the processes at work in other solar systems, which we
are
just beginning to discover," he said. "Probing the asteroid belt could
give us clues to these processes."

This research was funded in part by NASA.

Writer: , (765) 494-2081, cboutin@purdue.edu

Source: Michael E. Lipschutz, (765) 494-5326, rnaapunl@purdue.edu

Purdue News Service: (765) 494-2096; purduenews@purdue.edu
Related Web site:
Lipschutz's asteroid
<http://news.uns.purdue.edu/UNS/html3month/870722.Lipschutz.planet.html>

PHOTO CAPTION:

Purdue University's Michael E. Lipschutz analyzed enstatite chondrite
meteorites in a recent study of the materials near Earth at the dawn of
the solar system about 4.5 billion years ago. Data from the study may
offer clues into the conditions under which the Earth formed, evidence
of which no longer exists in terrestrial stone. (NASA photo/ID number
S91-41199)