Ancient Microorganisms Found in Halite May Have Implications for Search for
Life
Boulder, Colo., USA: Primary fluid inclusions in bedded halite from the
830-million-year-old Browne Formation of central Australia contain organic
solids and liquids, as documented with transmitted light and UV-vis
petrography. These objects are consistent in size, shape, and fluorescent
response to cells of prokaryotes and algae, and aggregates of organic
compounds. This discovery shows that microorganisms from saline
depositional environments can remain well preserved in halite over hundreds
of millions of years and can be detected in situ with optical methods
alone. This study has implications for the search for life in both
terrestrial and extraterrestrial chemical sedimentary rocks.
As halite crystals grow in saline surface waters, it traps parent water in
primary fluid inclusions. In addition to trapping parent waters, they can
trap any solids that were in the water near/on the crystal face. These
solids include tiny crystals of evaporite minerals or organics. Previous
studies of modern to Permian halites have documented the presence of
prokaryotic and eukaryotic organisms and organic compounds including beta
carotene.
This study uses non-destructive, optical techniques to identify and
document organic material in primary fluid inclusions in
830-million-year-old halite. Sara Schreder-Gomes, Kathleen Benison, and
Jeremiah Bernau had access to core samples from the Neoproterozoic Browne
Formation thanks to the Geological Survey of Western Australia.
The halite was well preserved and allowed them to examine halite crystals
from 10 halite beds from varying depths. They used transmitted light
petrography and UV-visible light petrography to identify primary fluid
inclusions and their contents. The team found that solids trapped in fluid
inclusions were consistent with prokaryotic and eukaryotic cells, and with
organic compounds, based on their size, shape, and fluorescent response to
UV-visible light.
This study reinforces the utility of non-destructive optical methods as a
first step in examining chemical sediments for biosignatures. The
petrographic context of fluid inclusions is vital to ensuring the contents
of fluid inclusions represent original parent waters and therefore are the
same age as the halite. This study also shows that microorganisms can be
preserved in fluid inclusions in halite for millions of years and suggests
that similar biosignatures may be able to be detected in chemical sediments
from Mars.
830-million-year-old microorganisms in primary fluid inclusions in
halite
Sara Schreder-Gomes; Kathleen Benison; Jeremiah Bernau
Contact: Sara Schreder-Gomes, sara.schreder-gomes@snc.edu, West Virginia
University, Geology and Geography, Morgantown, West Virginia
https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G49957.1/613521/830-million-year-old-microorganisms-in-primary
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