[meteorite-list] Dust In 'Earth's Attic' Could Hold Evidence Of Planet's Earliest Life

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:00:08 2004
Message-ID: <200207222129.OAA23718_at_zagami.jpl.nasa.gov>

http://www.washington.edu/newsroom/news/2002archive/07-02archive/k072202.html

Office of News and Information
University of Washington
Seattle, Washington

FROM: Vince Stricherz, 206-543-2580, vinces_at_u.washington.edu

FOR IMMEDIATE RELEASE: July 22, 2002

Dust in 'Earth's attic' could hold evidence of planet's earliest
life

The dust has been piling up in Earth's attic for billions of
years, and now some scientists want to sift through the
accumulation to see if they can find evidence of the planet's
earliest life.

"It is up there. I don't know how common it is, but somewhere up
there is at least one fist-sized chunk of rock with Earth's name
on it," said John Armstrong, a University of Washington doctoral
student in astronomy and astrobiology. "It would probably take
hundreds of years of human habitation to find it and recognize
it, but it's there."

"Up there" is the moon, what Armstrong and his colleagues refer
to as Earth's attic. And while he doesn't expect to actually find
a large chunk of Earth rock, he believes there is likely a wealth
of planetary debris in the form of fine particles on the moon's
surface.

In an upcoming edition of Icarus, an international journal of
solar system science, Armstrong and colleagues Llyd Wells, a UW
graduate student in oceanography, and Guillermo Gonzalez, an
assistant physics and astronomy professor at Iowa State
University, argue that humans should seriously consider returning
to lunar exploration. Any mission, they say, should include a
search for fossils of some of Earth's earliest microbial life.

In its very early history, 3.8 billion to 3.9 billion years ago,
comets and asteroids constantly bombarded the Earth. Some of
those bodies hit with such force that chunks of the planet's
surface were ejected beyond the pull of its gravity. The three
astrobiologists believe some of that ejected material went
directly to the lunar surface, while other material went into
orbit and some gradually fell to the moon.

Finding rocks, or even particles, from that period could be
invaluable in understanding how life on Earth came to be as it
is today, since any fossils found likely would be from a time
long before life on Earth developed great complexity and
diversity.

Because of the moon's position in the inner solar system, in
theory it has collected material from all the planets. Earth
matter probably is most abundant, since it is closest to the
moon, but Armstrong, Wells and Gonzalez expect that fallout
from Mars and Venus also is abundant enough that it could be
recovered. They have calculated that, on average, perhaps 22
tons of Earth material is spread over every 38 square miles
of the moon.

If they are right, Armstrong said, that means about 10 parts
per million of lunar material originated on Earth. However, it
would not necessarily be identifiable as Earth material. And
while material blasted directly to the moon probably came down
on the side facing Earth, any material that ended up in orbit
could have been deposited anywhere on the lunar surface.

"One thing we're still debating is where would be the best place
to look," Armstrong said.

The scientists believe Earth material from that long ago
probably became buried over time, so one strategy they have
devised is to look for recent craters in which old rocks have
been excavated. They also are searching through lunar samples
already returned to Earth, on the off chance those samples might
contain rocks that originated on the planet. They would be able
to tell by isotope ratios or by determining whether materials
in the rocks were formed in water -- something that cannot occur
on the moon.

At the very least, Armstrong hopes to find dust from pulverized
Earth rocks, material that can be dated and can give clues about
the history of bombardment by asteroids and meteors and how that
affected evolution. If materials are more intact, they might
contain interesting elements that would shed light on the early
Earth's environment and how life existed at that time. Less
likely, he said, would be the discovery of rare, volatile
elements that would tell about the early atmosphere. The
least likely find -- and the one most prized -- would be
microbiological fossils from 3.9 billion years ago.

"The part I like about this is that it makes the moon a window
on the early Earth," Armstrong said. "It also would give us
access to samples you can't get anywhere else at the moment."

Currently there are no plans for a U.S. mission to the moon,
though other nations are considering the possibility. It has
been 30 years since the National Aeronautics and Space
Administration's last manned mission, and three years since
the controlled crash of the robotic Lunar Prospector spacecraft
in a search for water on the moon.

Armstrong believes a new lunar mission would benefit science
on several levels and could help prepare and test systems for
eventual Martian exploration. To search for material of Earth
origin, he suggests the inclusion of a rover that could
systematically pass over a specific area, conduct tests and
prepare samples to be launched back to Earth. The only way
to find the Earth rocks, he said, is to find a way to look
specifically for them.

"If you find one of these things, it's going to be hard to
convince someone that it's of Earth origin," he said. "But if
you find more than one, then you can begin to classify them as
a group of materials and begin to make a more convincing case."

###

For more information, contact Armstrong at (206) 543-9039 or
jca_at_astro.washington.edu; Wells at (206) 543-0147 or
chimera1_at_ocean.washington.edu; or Gonzalez at (515) 294-5630
or gonzog_at_iastate.edu

IMAGE CAPTION:
[http://www.washington.edu/newsroom/news/images/lunar.jpg]
The moon as seen from the Stardust spacecraft during a flyby of
Earth in 2001. (Jet Propulsion Laboratory)
Received on Mon 22 Jul 2002 05:29:21 PM PDT