Bibcode
Westall, F.; Walsh, M. M.; McKay, D. S.; Wentworth, S.; Gibson, E. K.; Steele, A.; Toporski, J.; Lindstrom, D.; Martinez, R.; Allen, C. C.; Morris-Smith, P.; Thomas-Keprta, K.; Bell, M. S.
Referencia bibliográfica
Workshop on Mars 2001: Integrated Science in Preparation for Sample Return and Human Exploration, p. 109
Fecha de publicación:
1
1999
Número de citas
0
Número de citas referidas
0
Descripción
The rationale for looking for prokaryote fossils in Martian materials is
based on our present understanding of the environmental evolution of
that planet in comparison to the history of the terrestrial environments
and the development and evolution of life on Earth. On Earth we have
clear, albeit indirect, evidence of life in 3.8 b.y.-old rocks from
Greenland and the first morphological fossils in 3.3-3.5 b.y.-old cherts
from South Africa and Australia. In comparison, Mars, being smaller,
probably cooled down after initial aggregation faster than the Earth.
Consequently, there could have been liquid water on its surface earlier
than on Earth. With a similar exogenous and endogenous input of organics
and life-sustaining nutrients as is proposed for the Earth, life could
have arisen on that planet, possibly slightly earlier dm it did on
Earth. Whereas on Earth liquid water has remained at the surface of the
planet since about 4.4 b.y. (with some possible interregnums caused by
planet-sterilising impacts before 3.8. b.y. and perhaps a number of
periods of a totally frozen Earth, this was not the case with Mars.
Although it is not known exactly when surficial water disappeared from
the surface, there would have been sufficient time for life to have
developed into something similar to the terrestrial prokaryote stage.
However, given the earlier environmental deterioration, it is unlikely
that it evolved into the eukaryote stage and even evolution of oxygenic
photosynthesis may not have been reached. Thus, the impetus of research
is on single celled life simnilar to prokaryotes. We are investigating a
number of methods of trace element analysis with respect to the Early
Archaean microbial fossils. Preliminary neutron activation analysis of
carbonaceous layers in the Early Archaean cherts from South Africa and
Australia shows some partitioning of elements such as As, Sb, Cr with an
especial enrichment of lanthanides in a carbonaceous-rich banded iron
sediment . More significantly, preliminary TOF-SIMS investigations of
organics in the cherts reveals the presence of a biomarker, which
appears to be a derivative of bacterial polymer, in the carbonaceous
parts of the rocks. We conclude that a combination of morphological,
isotope and biogeochemical methods can be used to successfully identify
signs of life in terrestrial material, and that these methods will be
useful in searching for signs of life in extraterrestrial materials.