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Geologic Constraints on Early Mars Climate
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Journal Article
Geologic Constraints on Early Mars Climate
2019
Overview
Early Mars climate research has well-defined goals (MEPAG
2018
). Achieving these goals requires geologists and climate modelers to coordinate. Coordination is easier if results are expressed in terms of well-defined parameters. Key parameters include the following quantitative geologic constraints. (1) Cumulative post-3.4 Ga precipitation-sourced water runoff in some places exceeded
1
km
column. (2) There is no single Early Mars climate problem: the traces of ≥2 river-forming periods are seen. Relative to rivers that formed earlier in Mars history, rivers that formed later in Mars history are found preferentially at lower elevations, and show a stronger dependence on latitude. (3) The duration of the longest individual river-forming climate was
>
(
10
2
–
10
3
)
yr
, based on paleolake hydrology. (4) Peak runoff production was
>
0.1
mm
/
hr
. However, (5) peak runoff production was intermittent, sustained (in a given catchment) for only <10% of the duration of river-forming climates. (6) The cumulative number of wet years during the valley-network-forming period was
>
10
5
yr
. (7) Post-Noachian light-toned, layered sedimentary rocks took
>
10
7
yr
to accumulate. However, (8) an “average” place on Mars saw water for
<
10
7
yr
after the Noachian, suggesting that the river-forming climates were interspersed with long globally-dry intervals. (9) Geologic proxies for Early Mars atmospheric pressure indicate pressure was not less than 0.012 bar but not much more than 1 bar. A truth table of these geologic constraints versus currently published climate models shows that the late persistence of river-forming climates, combined with the long duration of individual lake-forming climates, is a challenge for most models.
Publisher
Springer Netherlands,Springer Nature B.V
