Ancient River on Mars leading to the Northern Ocean
On earth, we have definitive information by using stratigraphic principles; we can usually delineate rock units only in terms of their relative age to each other. We know younger rocks will be on the surface while the older ones will be under the surface as in strata of rock formations. Other methods, such as radiometric dating, are needed to determine absolute ages in geologic time on Earth. Assigning absolute ages to rock units on Mars is much more problematic. Numerous attempts have been made over the years to determine an absolute Martian chronology (timeline) by comparing estimated impact cratering rates for Mars to those on the Moon. If we know with precision the rate of impact crater formation on Mars by crater size per unit area over geologic time then crater densities also provide a way to determine absolute ages. Unfortunately, practical difficulties in crater counting and uncertainties in estimating the flux still create huge uncertainties in the ages derived from these methods. Martian meteorites have provided datable samples that are consistent with ages calculated thus far, but the locations on Mars from where these meteorites came (provenance) are unknown, limiting their value as chronostratigraphic tools. Absolute ages determined by crater density should therefore be taken with some skepticism.
Crater density timescale:
Pre-Noachian: Represents the interval from the accretion and differentiation of the planet about 4.5 (Gya.)billion years ago to the formation of the Hellas impact basin, between 4.1 to 3.8 Gya. Most of the geologic record of this interval has been erased by subsequent erosion and high impact rates. The crustal dichotomy is thought to have formed during this time, along with the Argyre and Isidis basins.
Noachian Period: Formation of the oldest extant surfaces of Mars between 4.1 and about 3.7 billion years ago (Gya): Noachian-aged surfaces are scarred by many large impact craters. The Tharsis bulge is thought to have formed during the Noachian, along with extensive erosion by liquid water producing river valley networks. Large lakes or oceans may have been present.
Hesperian Period: 3.7 to approximately 3.0 Gya. , marked by the formation of extensive lava plains. The formation of Olympus Mons probably began during this period. Catastrophic releases of water carved extensive outflow channels around Chryse Planitia and elsewhere. Ephemeral lakes or seas formed in the northern lowlands.
Amazonian Period: 3.0 Gya to present. The Amazonian regions have few meteorite impact craters but are otherwise quite varied. Lava flows, glacial/periglacial activity, and minor releases of liquid water continued during this period.
Mars Crater density time scale
Mineral alteration timescale:
In 2006, researchers using data from the OMEGA Visible and Infrared Mineralogical Mapping Spectrometer on board the Mars Express orbiter proposed an alternative Martian timescale based on the predominant type of mineral alteration that occurred on Mars due to different styles of chemical weathering in the planets past. They proposed dividing the history of the Mars into three eras: the Phyllocian, Theiikian and Siderikan.
Phyllocian: lasted from the formation of the planet until around the Early Noachian (about 4.0 Gya). OMEGA identified outcropping of phyllosilicates (clays) at numerous locations on Mars, all in rocks that were exclusively Pre-Noachian or Noachian in age (most notably in rock exposures in Nili Fossae and Mawrth Vallis). Phyllosillicates (clays) require a water-rich, alkaline environment to form. The Phyllocian era correlates with the age of valley network formation on Mars, suggesting an early climate that was conducive to the presence of abundant surface water. It is thought that deposits from this era are the best candidates in which to search for evidence of past life on the planet.
Theiikian: lasted until about 3.5 Gya. It was an era of extensive volcanism, which released large amounts of sulfur dioxide (SO2) into the atmosphere. The SO2 combined with water to create a sulphuric acid-rich environment that allowed the formation of hydrated sulphates (notably kieserite and gypsum).
Siderikan: lasted from 3.5 Gya until the present. With the decline of volcanism and available water, the most notable surface weathering process has been the slow oxidation of the iron-rich rocks by atmospheric peroxides producing the red iron oxides that give the planet its familiar color.
Mars Mineral Alteration Timescale
We see huge gaps in these geological timescales. Much of what we are looking for has been covered up or hard to find that is why we need geologists down on the planet doing the work not only rovers and satellites which are limited by the way they collect data. You will note that both timelines are almost the same, one with three periods and the other with four. This shows you how little we really know about the geological history of Mars.
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