Meteorites Offer Glimpse of the Early Earth, Say Purdue Scientists

http://news.uns.purdue.edu/UNS/html4...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,

Source: Michael E. Lipschutz, (765) 494-5326,

Purdue News Service: (765) 494-2096;
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)

I love this stuff and the way the casually drop zingers into it ...

"Shortly after the early Earth
formed, an object the size of Mars smashed into it,

I have never heard that before. Does anybody know where the evidence
for this Mars-sized is described. Unless that is the Mar-sized body
that splashed off the moon and formed the Pacific ocean, but I thought
those theories were defunct.

Best,

Michael

wrote:
I love this stuff and the way the casually drop zingers into it ...

"Shortly after the early Earth
formed, an object the size of Mars smashed into it,

I have never heard that before. Does anybody know where the evidence
for this Mars-sized is described.

Rumour has it that the banded iron formations will eventually be shown
to be the result of lunar impact or very close:-
"The whole-Earth scale of the structures and their rotational asymmetry
imply causational dynamics in opposition to the Earth's gravity,
reviving earlier speculation that protracted prograde Moon capture
during Archean to Proterozoic times may have caused the deformation.
In support are cited the pan-global distribution of banded iron
formations (as possible impact-related dust fall) virtually co-eval
with the ages of lunar impacts, the heavy cratering on the nearside of
the Moon, the obliquity of the rotational axes of both the Earth and
the Moon to the ecliptic, and the present ambital enlargement of the
Earth as a remnant related effect of the same forces that initiated the
disruptive tectonics."
But they need to be reinterpreted.
http://users.indigo.net.au/don/ee/abstract.html
http://users.indigo.net.au/don/ee/precursor.html
(Some event. Some dust fall)

Or check out the Moon Book for the Mars-size collision model (Heiken,
Vaniman and French)


Unless that is the Mar-sized body
that splashed off the moon and formed the Pacific ocean, but I thought
those theories were defunct.

Best,

Michael

The whole-Earth scale of the structures

That's another thing I love -- guys who look at the big picture. What
structures are they referring to?

Are not the bands and layers in the banded iron formations evidence
that their formation was a result of a cyclical process. BIF origins
are complicated, but how would be a catastrophically-captured moon
would help describe what we see. I thought the banded iron formations
were linked to early life producing oxygen and the rise of oxygen in
the early atmosphere. Wouldn't a Mars-sized body crashing down
seriously set back the progress of life?

during Archean to Proterozoic times

That's a long period. When did it come crashing in -- We would be
right back into the Hadean? Shouldn't there be better evidence for the
crash if it came down during the Proterozoic. I would expect
shattercones everywhere in Precambrian rocks and some kind of
disruption or anomaly on the far side of the planet.

Michael

In article .com,
wrote:
"Shortly after the early Earth
formed, an object the size of Mars smashed into it,

I have never heard that before. Does anybody know where the evidence
for this Mars-sized is described. Unless that is the Mar-sized body
that splashed off the moon and formed the Pacific ocean, but I thought
those theories were defunct.

You're confusing two different theories, I think.

The theory that the Pacific Ocean and the Moon were connected somehow is
long defunct. It died with the rise of plate tectonics: the Pacific is a
relatively recent feature of Earth. (Earth has long had big oceans, but
the details have varied greatly over time as the continents have shuffled
around.)

The theory that the Moon is mantle rock splashed up from an off-center
impact by a Mars-sized body is widely believed because it's about the only
credible theory of the Moon's origin. All the others were destroyed by
the Apollo samples: the Moon's rocks are too Earthlike to have had an
independent origin, and too different to have had a similar history
(notably, they were severely baked sometime quite early). The giant-
impact theory is the only one that fits all the data.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

wrote in message
oups.com...
The whole-Earth scale of the structures

That's another thing I love -- guys who look at the big picture. What
structures are they referring to?

What are you referring to? I have found no reference in that report to
"whole-Earth scale".

Are not the bands and layers in the banded iron formations evidence
that their formation was a result of a cyclical process. BIF origins
are complicated, but how would be a catastrophically-captured moon
would help describe what we see. I thought the banded iron formations
were linked to early life producing oxygen and the rise of oxygen in
the early atmosphere. Wouldn't a Mars-sized body crashing down
seriously set back the progress of life?

The banded Iron formations are only 2 billion years old. The earth is 4.54
billion years old. The collision occured during its early formation,
according to the theory, when it was still in its accretionary phase.

wrote:
The whole-Earth scale of the structures

That's another thing I love -- guys who look at the big picture. What
structures are they referring to?

BIG PICTURE- You're looking at the reasons for the demise of plate
tectonics and its substitution by Earth expansion. The dedicated
followers of fashion on this ng are still with plate tectonics because
they've forgotten (if they ever knew) how to think, and are much too
concerned with each other's bums. The structures involved are those
describing the break-up of the Mesozoic crust (ocean floors and
mountain belts) and the balance between 'uplift' of continental
platforms and their erosion ("whole-Earth" through geological time).
The pattern can be extrapolated right back the Phanerozoic and probably
into the Proterozoic. The picture very closely relates to the
evolution of the planet. Hence "Whole-Earth". That's Earth expansion.
It relates the geological history of the Earth to gravitational -
rotational imbalance and its position in the solar system Plate
Tectonics ignores this connection, seeing the geological history more
anatomically, and related to internal convection in the mantle
('indigestion')

So, ..Whole-Earth structu its differentiated layering, its oblate
shape, the global break-up of the mantle (spreading ridges/ transform
fault sets/ zones of crust-mantle overriding (earlier called
'subduction zones'), the remants of Mesozoic crustal collapse, the
entirety of stratigraphic sequence, ... everything in fact. And yes,
you have to look at it as a whole as the big picture. You lose it if
you look at the elemental parts (Plate Tectonics)


Are not the bands and layers in the banded iron formations evidence
that their formation was a result of a cyclical process.

Yes, indeed. What could be more cyclical than the accumulation of
Earth-Moon dust? Mars-sized object slams into the planet, through the
crust, the mantle, and right to the core, knocking off a piece and
throwing up an iron plasma. (The Earth was a lot smaller then with very
little stratigraphic sequence, only Archaean crust riddled with
greenstone belts (mantle intrusions/ effusions). Mantle was much
thinner.) Much plasma escapes the gravitational field. So there we
have a picture of two planetary bodies now, encased in dust,
travelling through the solar system, and every year picking up a new
charge of settling dust. Settling dust - Every day, Every month,
Every Year, and comming back regularly for a re-charge. What could be
more 'seasonally cyclical' cyclical than that?


BIF origins
are complicated, but how would be a catastrophically-captured moon
would help describe what we see. I thought the banded iron formations
were linked to early life producing oxygen and the rise of oxygen in
the early atmosphere.

Yes, ..I know, that's what they say, when they put it under the
microscope, and of course it has to accummulate in water, but they
can't even tell whether they're looking at iron grains or biological
residue. But when you look at the bigger (whole-Earth) picture, the
spread of ages related to those of Lunar impacts (and all those
phenomenal craters on the Moon), and the areal/ temporal distribution,
and take into account all the micrometeorites they're finding in the
interbeds, you have to wonder at what they've got for marbles by
sticking to their story. The banded iron formations is the legacy on
Earth of what we can see on the Moon all the way from here. Once
people get an eye for them, they'll be seeing evidence everyshe-

"Evidence for four impacts even older than than Vredefort, that
occurred 3.2 to 3.5 billion years ago, has been found in the greenstone
rocks around Barberton in South Africa and corresponding rocks in the
eastern Pilbara block of Western Australia. However, these impacts are
no longer recognizable as structures on the surface like Vredefort's."


Wouldn't a Mars-sized body crashing down
seriously set back the progress of life?

I guess, ..if there was any. (Might even start it. )


during Archean to Proterozoic times

That's a long period. When did it come crashing in -- We would be
right back into the Hadean? Shouldn't there be better evidence for the
crash if it came down during the Proterozoic.

Banded iron formations have a spread of age maxima, with the oldest
ones being somewhere around 3.8by. The spread is slightly offset from
that worked out for lunar impacts, so that discrepancy and the hubris
of human error in suchlike matters will be used by those with no
imagination or common sense, to discredit the notion of a correlation.
That's why I said it was just a rumour just now (being spread by me).
After all that money being spent on getting to the Moon they've worked
out the Mars impactor thing as a 'best fit' model for the origin of the
Moon, but for some reason don't link it to that unique
near-contemporaneous stratigraphic history. They still have to waken
up on that one. I'm a bit more flexible whether it was a third party
or the Moon itself, because (of this whole_Earth thing again)
everything that we see at the present day ties right back to then.
Whatever happened, the repercussions are still going on, and appear to
be accellerating. That's why I go for fly-by. Impact or fly-by - I
don't much bother. I find a 'hit' difficult to envisage without the
whole lot disintetrating to another asteroidal belt or whatever.
Either way it would have been pretty catastrophic. I believe it has
been calculated that if it was retrograde capture, Earth would have
been vaporised. Even at the size it is now. So, .. But I do
think capture is a bit iffy, though I suggest it on my site. Maybe
being a 'clump' of sorts that got kicked out of some original orbit
(links to asteroid belt? the third planet model? ..who knows..)


I would expect
shattercones everywhere in Precambrian rocks and some kind of
disruption or anomaly on the far side of the planet.

Depends how brittle or mushy I guess, how rapid the hit. You know how
when you throw a stone high in the air so that zips through the surface
of the water almost without a mark..? What sort of shock absorbption
is that, compared to a more 'noisy' one? Would there be a difference?
Personally I reckon Spinifex textures in the Archaean ultramafics are
best interpreted as stress-textures of sorts, either shock or pressure
release or metamorphic textures of some sort (this one from the
archives, from years back):-
http://users.indigo.net.au/don/ore/spinifexshock.html
(but that's another bandwagon like plate tectonics/ orogensis/
isostacy/ etc that people can't see past.) There's a whole spectrum
from crystallites in glass in ramifying veinlets to large interlocking
laths overprinting schistosity in entire stratigraphic sequences.
"Quenching" is usually touted as a heat thing, when stress (to me)
seems much more likely.


Michael