Martian meteorite's organic materials origin not biological, formed by geochemical interactions between water and rock
The search for life on Mars can teach us about the reactions that led to
the building blocks of life on early Earth

Date:
January 13, 2022
Source:
Carnegie Institution for Science
Summary:
Organic molecules found in a meteorite that hurtled to Earth
from Mars were synthesized during interactions between water and
rocks that occurred on the Red Planet about 4 billion years ago,
according to new analysis.



FULL STORY ========================================================================== Organic molecules found in a meteorite that hurtled to Earth from Mars
were synthesized during interactions between water and rocks that occurred
on the Red Planet about 4 billion years ago, according to new analysis
led by Carnegie's Andrew Steele and published by Science.


==========================================================================
The meteorite, called Allan Hills (ALH) 84001, was discovered in the
Antarctic in 1984 and is considered one of the oldest known projectiles
to reach Earth from Mars.

"Analyzing the origin of the meteorite's minerals can serve as a window to reveal both the geochemical processes occurring early in Earth's history
and Mars' potential for habitability," explained Steele, who has done
extensive research on organic material in Martian meteorites and is a
member of both the Perseverance and Curiosity rovers' science teams.

Organic molecules contain carbon and hydrogen, and sometimes include
oxygen, nitrogen, sulfur, and other elements. Organic compounds
are commonly associated with life, although they can be created by non-biological processes as well, which are referred to as abiotic
organic chemistry.

For years, scientists have debated the origin story for the organic
carbon found in the Allan Hills 84001 meteorite, with possibilities
including various abiotic process related to volcanic activity, impact
events on Mars, or hydrological exposure, as well as potentially the
remnants of ancient life forms on Mars or contamination from its crash
landing on Earth.

The Steele-led team, which also included Carnegie's Larry Nittler,
Jianhua Wang, Pamela Conrad, Suzy Vitale, and Vincent Riggi as well
as researchers from GFZ German Research Centre for Geosciences, Free
University of Berlin, NASA Johnson Space Center, NASA Ames Research
Center, and Rensselaer Polytechnic Institute, used a variety of
sophisticated sample preparation and analysis techniques -- including co-located nanoscale imaging, isotopic analysis, and spectroscopy -- to
reveal the origin of organic molecules in the Allan Hills 84001 meteorite.

They found evidence of water-rock interactions similar to those that
happen on Earth. The samples indicate that the Martian rocks experienced
two important geochemical processes. One, called serpentinization,
occurs when iron- or magnesium-rich igneous rocks chemically interact
with circulating water, changing their mineralogy and producing hydrogen
in the process. The other, called carbonization, involves interaction
between rocks and slightly acidic water containing dissolved carbon
dioxide and results in the formation of carbonate minerals.

It is unclear whether these processes were induced by surrounding aqueous conditions simultaneously or sequentially, but the evidence indicates
that the interactions between water and rocks did not occur over a
prolonged period.

What is evident, however, is that the reactions produced organic material
from the reduction of carbon dioxide.

These mineralogical features are rare in Martian meteorites, and while carbonation and serpentinization have been shown in orbital surveys
of Mars and carbonation has been found in other, less-ancient, Martian meteorites, this is the first instance of these processes occurring in
samples from ancient Mars.

Organic molecules have been detected by Steele in other Martian meteorites
and from his work with the Sample Analysis at Mars (SAM) team on the
Curiosity rover, indicating that abiotic synthesis of organic molecules
has been a part of Martian geochemistry for much of the planet's history.

"These kinds of non-biological, geological reactions are responsible
for a pool of organic carbon compounds from which life could have
evolved and represent a background signal that must be taken into
consideration when searching for evidence of past life on Mars," Steele concluded. "Furthermore, if these reactions happened on ancient Mars,
they must have happened on ancient Earth, and could possibly explain
the results from Saturn's moon Enceladus as well.

All that is required for this type of organic synthesis is for a brine
that contains dissolved carbon dioxide to percolate through igneous
rocks. The search for life on Mars is not just an attempt to answer the question 'are we alone?' It also relates to early Earth environments and addresses the question of 'where did we come from?'" The US Antarctic meteorite samples were recovered by the Antarctic Search for Meteorites (ANSMET) program, which has been funded by NSF and NASA and characterized
and curated by the Department of Mineral Sciences of the Smithsonian Institution and the Astromaterials Acquisition and Curation Office at
NASA Johnson Space Center, respectively.

This work was funded by NASA, Carnegie's Earth and Planets Laboratory,
and the Helmholtz Recruiting Initiative program.

========================================================================== Story Source: Materials provided by
Carnegie_Institution_for_Science. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. A. Steele et al. Organic synthesis associated with serpentinization
and
carbonation on early Mars. Science, 2022 DOI:
10.1126/science.abg7905 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220113151349.htm
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