B. Ashley Zauderer
AstroTerps Conference, Fall '04
U. of Maryland, Dept. of Astronomy

 
"Rummaging through Earth's Attic for Remains of Ancient Life"
John C. Armstrong,  Lloyd E. Wells and Guillermo Gonzalez
Icarus 160, 183-196 (2002).

Abstract:
The sequence of events that led to the development of a habitable zone
on the Earth and the development of complex, diverse, and even
intelligent life seems to be precisely ordered.  We are now trying to
piece together this jigsaw puzzle, which is extraordinarily
challenging because many pieces are missing or have changed over time.
We hope to present evidence that sheds light on one of these pieces.

With many missing pieces and hence many degrees of freedom, any
constraint on the system is invaluable.  For example, new research
shows that rapid variations between tidal flooding and drying (on the
order of hours), "could have provided a driving force for cyclic
replication of early biomolecules" (Lathe 2004).  And this cyclic
variation is hypothesized to have come about from rapid rotation of
the Earth (between 2 and 6 hours), resulting from the theorized major 
impact that created the moon.  However, recent hydrodynamic
simulations show that a large moon-creating impact would have most
likely occurred when the Earth was over 95% accreted (Canup 2004).  
Lathe also cites that other things could lead to the development of
life, namely submarine hot springs or seeding.  Each individual clue
must fit into place in order to re-construct the actual sequence of
events that led to the devlopment of life on Earth.

And this is where the Earth's moon becomes invaluable.  Like the attic
in a grandmother's house, not much that gets to the moon is disposed
of, although the reasons vary significantly!  For the latter, junk
stays around becaue the moon does not have an atmosphere or much
geologic activity on the surface.  Infalling meteorites from
intersolar space during the period of heavy bombardment could easily
be from the Earth, Mercury or Venus.  However, everything gets jumbled
up in the regolith, as impacts have continued, making a search difficult.  
 
Armstrong, Wells and Gonzalez make a statistical argument in the paper
we examine why a mission should be funded that would involve a careful
search of the moon's regolith for ancient debris from early in the
solar system.  If the debris from long ago could be sorted from the
more recent debris, much could be learned about the early geochemical
and biological state of the planets' formation history.  
They consider the parameters that will affect
the likelihood of finding clues on the moon:  the amount of ejecta
from the proto-planets that could have been "swept up" by the moon
over its history as well as the likelihood of survival of any tracers 
of early building blocks of life.  


Canup, Robin M.  Icarus 168 (2004) 433-456.
Lathe, Richard.  Icarus 168 (2004) 18-22.