Noachian (4.1 – 3.7 billion years ago)
The Noachian Period is named after Noachis Terra, an ancient highland region located between the huge Argyre and Hellas impact basins of the southern hemisphere.
This was still a period of heavy bombardment, with numerous asteroid and comet impacts. These created the Hellas, Isidis and Argyre basins, the largest impact structures still visible on the planet today, as well as many of the craters that pockmark the southern highlands.
At the same time, large-scale volcanic activity was taking place in the Tharsis region and parts of the highlands. The growth of the Tharsis bulge – home to Arsia Mons, Pavonis Mons and Ascraeus Mons, some of the largest volcanoes in the Solar System – coincided with widespread fracturing of the surface and the creation of the giant rift valley system known as Valles Marineris.
The volcanic eruptions poured ash and gases into the atmosphere. As the thicker blanket of air trapped more solar heat, the planet warmed. Clouds probably developed and precipitation rained to the ground. Many of the valley networks on Mars date from this period, and lakes seem to have formed in many basins and craters. There may even have been a shallow ocean covering at least part of the northern lowlands.
Surface rovers have found evidence to indicate that many rocks were chemically altered by periodic or prolonged exposure to non-acidic ground water. This led to the formation of clay minerals, known as phyllosilicates.
Meanwhile, as the interior of the planet cooled and its magnetic dynamo shut down, Mars no longer retained a global magnetic field.
Habitable environments gradually became smaller and more localised, but Noachian surface conditions continued to be favourable for the emergence of life.
Guest “what a cool field trip this would be!” by David Middleton
An ancient river on Mars may have flowed for 100,000 years
SPACE 5 May 2020
By Donna Lu
We know from images of Mars’s surface that the planet once had plenty of flowing water, but now we’ve found the first evidence of a river that was there for more than 100,000 years.
Francesco Salese at Utrecht University in the Netherlands and his colleagues discovered a high rocky cliff in the north-western rim of Mars’s Hellas basin that seems to have been formed gradually by the flow of an ancient river.
As rivers moves, they deposit sediment that builds up in layers. The rocky outcrop is 200 metres high – about twice the height of the White Cliffs of Dover – and 1.5 kilometres wide. The sedimentary rocks of the cliff are an estimated 3.7 billion years old. For something of this size to form, it would have required a river that was active for at least 100,000 Earth years.[…]
“To form these 200-metre-thick deposits we needed conditions that would have required an environment capable of maintaining significant volumes of liquid water,” says Salese. That means the water would have flowed year round, which suggests that Mars once had a water cycle driven by precipitation, similar to that of Earth.[…]
Read more: https://www.newscientist.com/article/2242630-an-ancient-river-on-mars-may-have-flowed-for-100000-years/#ixzz6LgSTnSPT
The full text of the paper, Salese et al., 2020, is available and literally “rocks!” (Whenever anyone says “literally,” they almost always mean figuratively.)
This image is from the New Scientist article:
This appears to be an erosional exposure of a sedimentary rock sequence, most likely of fluvial origin, covered by subsequent lava flows.
In this study, we use high-resolution imaging science experiment (HiRISE) image (25 cm/pixel) and topographic (1 m/pixel) data to describe the sedimentary-stratigraphic architecture of a far-larger, 1500-m-wide, 190-m-thick sedimentary succession. The recently identified Izola outcrop is located in the northwestern rim of the Hellas basin (Fig. 1a), a ~2000 km diameter impact structure containing a variety of 3.7 Ga Noachian Fe/Mg phyllosilicate-rich sedimentary intercrater plains, overlain by Hesperian-aged (~3.3 Ga) lava flows19.
These intercrater plains offer erosional windows which expose stratigraphic sections with well-preserved channel forms, and which must be older than the ~3.7 Ga overlying plains19. The channel forms and associated sedimentary packages are interpreted as the product of an actively depositing fluvial system, with the final sedimentary architecture suggesting that these Noachian-aged rivers were not typified by high-energy episodic floods, but rather perennial or semi-perennial fluvial flow. The scale and completeness of the sedimentary succession offers a so far unique opportunity to assess the larger scale morphology of an evolving Noachian-aged fluvial system.
Salese et al., 2020
The detail of the sedimentary architecture is stunning.
Hopefully the Mars Perseverance Rover will launch on schedule, this summer. It will explore Jezero crater, where evidence of both clay mineralogy (phyllosilicates) and lacustrine carbonates have been detected. Perseverance will cache rock and regolith samples for future recovery.
Salese, F., McMahon, W.J., Balme, M.R. et al. Sustained fluvial deposition recorded in Mars’ Noachian stratigraphic record. Nat Commun 11, 2067 (2020). https://doi.org/10.1038/s41467-020-15622-0