FOR
IMMEDIATE RELEASE Contact:
Martian meteorite mineral not made by
organisms
Claims that tiny crystals of iron oxide in a martian meteorite were formed by organisms on Mars are
incorrect, according to a new study published today. Two scientists at the
Since the startling report in 1996 by NASA
scientists of possible evidence for life in the Martian meteorite ALH84001,
attention has become increasingly focussed on the origin of tiny crystals of an
iron oxide called magnetite as they appeared to provide the most compelling
evidence for Martian life. The magnetite crystals are remarkably similar in
size, shape and composition to the tiny magnetites used by bacteria as
compasses to help them navigate through pools of water, and seemingly unlike
all other known iron oxides in rocks.
The new study of ALH84001 by David Barber and Ed
Scott, which is published in the Proceedings of the National Academy of
Sciences USA, shows that the planes of oxygen atoms in the magnetite crystals
are beautifully aligned with those in the surrounding carbonate crystal. This proves that the magnetite crystals could
not have formed elsewhere and then been deposited in the carbonate, as the NASA
scientists argued. They must have formed
exactly where they are observed today in the carbonate.
Barber and Scott also discovered oriented
crystals of magnesium oxide in the martian carbonate
and conclude that the iron and magnesium oxides both formed when the carbonate
was hot and had partly decomposed to form carbon dioxide gas. Since the meteorite was heated by an impact
on Mars 4.0 billion years old that melted and vaporized many minerals in the
rock, Barber and Scott infer that the iron and magnesium oxides formed then.
Martian organisms cannot be responsible for the size and shape of any magnetite
crystal in ALH84001.
Does this result mean
that the most famous meteorite will now be returning to obscurity? Absolutely not, according to Scott. “Meteorites are cosmic gifts that keep on
giving, and giving!” ALH 84001 is the oldest rock we have from any planet as it
crystallized over 4.4 billion years ago and it surely contains clues to many
mysteries about the solar system. For
example, if Mars and the Moon were both bombarded by asteroids 4.0 billion
years ago, why should we find an ancient meteorite from Mars but no equally
ancient lunar meteorites or returned samples from the Moon of comparable
size? Can the magnetite crystals in
ALH84001 tell us the strength of the magnetic field on Mars 4.0 billion years
ago? An ancient Martian rock, even one
that has apparently failed to bring evidence of extra-terrestrial life, is a
precious gift.
For
more information read:
Planetary Science Research Discoveries:
http://www.psrd.hawaii.edu/May02/ALH84001magnetite.html
Proceedings of the National Academy of Sciences,
http://www.pnas.org/cgi/content/full/99/10/6556
Ed
Scott 1-808-956-3955 escott@pgd.hawaii.edu