Araxes Geological History

Araxes Geological History.

The geological history of Araxes employs observations, indirect and direct measurements, and various inferometry techniques to estimate the physical evolution of Araxes. Early Imperium efforts by Nicholas Steno, included superposition and stratigraphy, have being actively applied to the data available from several Araxian observational and measurement resources. These include the landers, orbiting platforms, out of system-based observations and Araxian meteorites.

Observations of the surfaces of many Solar System bodies reveals important clues about their evolution. For example, a lava flow that spreads out and fills a large impact crater is likely to be younger than the crater. On the other hand, a small crater on top of the same lava flow is likely to be younger than both the lava and the larger crater since it can be surmised to have been the product of a later, unobserved, geological event. This principle, called the law of superposition, and other principles of stratigraphy, first formulated by Imperium Geologist Nicholas Steno in antiquity, allowed later geologists to divide geological history of a planet into various eras. The same methodology was later applied to Araxes.

Another stratigraphic principle used on planets where impact craters are well preserved is that of crater number density. The number of craters greater than a given size per unit surface area (usually million km2) provides a relative age for that surface. Heavily cratered surfaces are old, and sparsely cratered surfaces are young. Old surfaces have a lot of big craters, and young surfaces have mostly small craters or none at all.

These stratigraphic concepts form the basis for the Araxian geologic timescale.

Stratigraphy

Stratigraphy establishes the relative ages of layers of rock and sediment by denoting differences in composition (solids, liquids, and trapped gasses). Assumptions are often incorporated about the rate of deposition, which generates a range of potential age estimates across any set of observed sediment layers.

The primary technique for calibrating the ages to the Common Era calendar is radiometric dating. Combinations of different radioactive materials can improve the uncertainty in an age estimate based on any one isotope.

By using stratigraphic principles, rock units' ages can usually only be determined relative to each other. For example, knowing that Mesozoic rock strata making up the Cretaceous System lie on top of (and are therefore younger than) rocks of the Jurassic System reveals nothing about how long ago the Cretaceous or Jurassic Periods were. Other methods, such as radiometric dating, are needed to determine absolute ages in geologic time. Generally, this is only known for rocks on the Earth. Absolute ages are also known for selected rock units of the Moon based on samples returned to Earth.

Assigning absolute ages to rock units on Araxes is much more problematic. Numerous attempts have been made over the years to determine an absolute Araxian chronology (timeline) by comparing estimated impact cratering rates for Araxes to those on the Moon. If the rate of impact crater formation on Araxes by crater size per unit area over geologic time (the production rate or flux) is known with precision, 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. Araxian meteorites have provided datable samples that are consistent with ages calculated thus far, but the locations on Araxes from where the 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

Studies of impact crater densities on the Araxian surface have delineated three broad periods in the planet's geologic history. The periods were named after places on Araxes that have large-scale surface features, such as large craters or widespread lava flows, that date back to these time periods. The absolute ages given here are only approximate. From oldest to youngest, the time periods are:

The Pre-Noachian represents the interval from the accretion and differentiation of the planet to the formation of the Hellas impact basin about 400 million years later. 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.

The Noachian Period formed the oldest extant surfaces of Araxes between 400 Million years to 800 million years after the accretion and differentiation of the planet. 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.

The Hesperian Period formed approximately 800 million years to approximately 1.5 Billion years after the accretion and differentiation of the planet. 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.

The Amazonian Period began approximately 1.5 Billion years after the accretion and differentiation of the planet to the present time. Amazonian regions have few meteorite impact craters but are otherwise quite varied. Lava flows, glacial/periglacial activity, and releases of liquid water continued during this period.

The date of the Hesperian/Amazonian boundary is particularly uncertain. The Hesperian is thought of as a transitional period between the end of heavy bombardment of the Noachian and the cold, dry Araxes seen today in the Amazonian Period.

Researchers using data from the OMEGA Visible and Infrared Mineralogical Mapping Spectrometer proposed an alternative Araxian timescale based on the predominant type of mineral alteration that occurred on Araxes due to different styles of chemical weathering in the planet’s past. They proposed dividing the history of the Araxes into three eras: the Phyllocian, Theiikian and Siderikan.

Phyllocian (named after phyllosilicate or clay minerals that characterize the era) lasted from the formation of the planet until around the Early Noachian (ending about 500 Million years after the accretion and differentiation of the planet). OMEGA identified outcropping of phyllosilicates at numerous locations on Araxes, all in rocks that were exclusively Pre-Noachian or Noachian in age (most notably in rock exposures in Nili Fossae and Mawrth Vallis). Phyllosillicates require a water-rich, alkaline environment to form. The Phyllocian era correlates with the age of valley network formation on Araxes, 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 (named after sulphurous in Greek, for the sulphate minerals that were formed) lasted from about 500 Million years until about One Billion years after the accretion and differentiation of the planet. It was an era of extensive volcanism, which released large amounts of sulphur 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 (named for iron in Greek, for the iron oxides that formed) began One Billion years after the accretion and differentiation of the planet 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 colour.

Early Pre-Noachian Period: 0 - 100 Million Years after planetary crust formation

Mid Pre-Noachian Period: 100 - 200 Million Years after planetary crust formation

Late Pre-Noachian Period: 200 - 400 Million Years after planetary crust formation

Early Noachian Period: 400 - 500 Million Years after planetary crust formation

Mid Noachian Period: 500 - 640 Million Years after planetary crust formation

Late Noachian Period: 640 - 800 Million Years after planetary crust formation

Early Hesperian Period: 800 - 1100 Million Years after planetary crust formation.

Late Hesperian Period: 1.1 - 1.5 Billion Years after planetary crust formation.

Early Amazonian Period: 1.5 Billion Years after planetary crust formation until the present.

Early Phyllocian Period: 0 - 125 Million years after the accretion and differentiation of the planet.

Mid Phyllocian Period: 125 - 250 Million years after the accretion and differentiation of the planet.

Late Phyllocian Period: 250 - 500 Million years after the accretion and differentiation of the planet.

Early Theiikian Period: 500 - 640 Million years after the accretion and differentiation of the planet.

Mid Theiikian Period: 640 - 800 Million years after the accretion and differentiation of the planet.

Late Theiikian Period: 800 - 1000 Million years after the accretion and differentiation of the planet.

Early Siderikan Period: 1.0 - 1.25 Billion years after the accretion and differentiation of the planet.

Mid Siderikan Period: 1.25 - 1.6 Billion years after the accretion and differentiation of the planet.

Late Siderikan Period: 1.6 Billion years after the accretion and differentiation of the planet until present.

Two different dating system might seem confusing at first glance, but because they use different but independent methodologies, they can assist in narrowing down a date range. For example, a strata demonstrating conditions consistent with Mid Pre-Noachian: 100 - 200 Million Years after planetary crust formation but also characteristics of Early Phyllocian Period: 0 - 125 Million years after the accretion and differentiation of the planet; then one can estimate for comparison purposes a date of 100-125 years after the accretion and differentiation of the planet due to the date range crossover. Irreconcilable or non-crossing date ranges usually indicates the need to re-examine methodology or look for other means to cross reference.

1. Noachian Period

The Noachian is a geologic system and early time period on the planet Araxes characterized by high rates of meteorite and asteroid impacts and the possible presence of abundant surface water. The absolute age of the Noachian period is uncertain but probably corresponds to the Late Heavy Bombardment. Many of the large impact basins on Araxes formed at this time. The Noachian Period is roughly equivalent to the Hadean and early Archean eons when the first life forms likely arose.

Noachian-aged terrains on Araxes are prime spacecraft landing sites to search for fossil evidence of life. During the Noachian, the atmosphere of Araxes was denser than it was during the colonization era, but thinner than we are accustomed to today, and the climate warm enough to allow rainfall, but cool enough to allow surface water to stay. Large lakes and rivers were present in the southern hemisphere, and an ocean covered the low-lying northern plains. Extensive volcanism occurred in the Tharsis region, building up enormous masses of volcanic material (the Tharsis bulge) and releasing large quantities of gases into the atmosphere. Weathering of surface rocks produced a diversity of clay minerals (phyllosilicates) that formed under chemical conditions conducive to microbial life.

At a large scale (>100 m), Noachian surfaces are very hilly and rugged, superficially resembling typical lunar highlands. Noachian terrains consist of overlapping and interbedded ejecta blankets of many old craters. Mountainous rim materials and uplifted basement rock from large impact basins are also common. The number-density of large impact craters is very high, with about 400 craters greater than 8 km in diameter per million km^2. Noachian-aged units cover 45% of the Araxian surface; they occur mainly in the southern highlands of the planet, but are also present over large areas in the north, such as in Tempe and Xanthe Terrae, Acheron Fossae, and around the Isidis basin (Libya Montes).

Across many areas of the planet, the top of the Noachian System is overlain by more sparsely cratered, ridged plains materials interpreted to be vast flood basalts similar in makeup to lunar maria. These ridged plains form the base of the younger Hesperian System. The lower stratigraphic boundary of the Noachian System is not formally defined. The system was conceived originally to encompass rock units dating back to the original formation of the crust. Work by Herbert Frey using Araxes Orbital Laser Altimeter (MOLA) data indicates that the southern highlands of Araxes contain numerous buried impact basins (called quasi-circular depressions, or QCDs) that are older than the visible Noachian-aged surfaces and that pre-date the Hellas impact. Herbert Frey suggests that the Hellas impact should mark the base of the Noachian System. If Frey is correct, then much of the bedrock in the Araxian highlands is pre-Noachian in age, dating back to up to 400 million years after the formation of the planetary crust.

The Noachian System is subdivided into three chronostratigraphic series: Lower Noachian, Middle Noachian, and Upper Noachian. The series are based on referents or locations on the planet where surface units indicate a distinctive geological episode, recognizable in time by cratering age and stratigraphic position. For example, the referent for the Upper Noachian is an area of smooth intercrater plains east of the Argyre basin. The plains overlie (are younger than) the more rugged cratered terrain of the Middle Noachian and underlie (are older than) the less cratered, ridged plains of the Lower Hesperian Series. The corresponding geologic time (geochronological) units of the three Noachian series are the Early Noachian, Mid Noachian, and Late Noachian Periods. Note that a Period is a subdivision of a period; the two terms are not synonymous in formal stratigraphy.

Early Noachian: 400-500 Million Years after planetary crust formation

Mid Noachian: 500-640 Million Years after planetary crust formation

Late Noachian: 640-800 Million Years after planetary crust formation

The scheme of formal stratigraphic nomenclature has been successfully applied to Araxes for several decades now but has numerous flaws. The scheme will no doubt become refined or replaced as more and better data become available. Obtaining radiometric ages on samples from identified surface units is clearly necessary for a more complete understanding of Araxian history and chronology.

The Noachian Period is distinguished from later periods by high rates of impacts, erosion, valley formation, volcanic activity, and weathering of surface rocks to produce abundant phyllosilicates (clay minerals). These processes imply a wetter global climate with at least episodic warm conditions.

The cratering record suggests that the rate of impacts in the Inner Solar System 500 million years after the crust formation was 500 times higher than today. During the Noachian, about one 100-km diameter crater formed on Araxes every million years, with the rate of smaller impacts exponentially higher. Such high impact rates would have fractured the crust to depths of several kilometers and left thick ejecta deposits across the planet’s surface. Large impacts would have profoundly affected the climate by releasing huge quantities of hot ejecta that heated the atmosphere and surface to high temperatures. High impact rates probably played a role in removing much of Araxes’ early atmosphere through impact erosion.

Frequent impacts produced a zone of fractured bedrock and breccias in the upper crust called the megaregolith. The high porosity and permeability of the megaregolith permitted the deep infiltration of groundwater. Impact-generated heat reacting with the groundwater produced long-lived hydrothermal systems that would have been exploited by thermophilic microorganisms. Computer models of heat and fluid transport in the ancient Araxian crust suggest that the lifetime of an impact-generated hydrothermal system could be hundreds of thousands to millions of years after impact.

Most large Noachian craters have a worn appearance, with highly eroded rims and sediment-filled interiors. The degraded state of Noachian craters, compared with the nearly pristine appearance of Hesperian craters only a few hundred million years younger, indicates that erosion rates were higher (approximately 1000 to 100,000 times) in the Noachian than in subsequent periods. The presence of partially eroded (etched) terrain in the southern highlands indicates that up to 1 km of material was eroded during the Noachian Period. These high erosion rates, though still lower than average terrestrial rates, are thought to reflect wetter and perhaps warmer environmental conditions.

The high erosion rates during the Noachian may have been due to precipitation and surface runoff. Many (but not all) Noachian-aged terrains on Araxes are densely dissected by valley networks. Valley networks are branching systems of valleys that superficially resemble terrestrial river drainage basins. Although their principal origin (rainfall erosion, groundwater sapping, or snow melt) is still debated, valley networks are rare in subsequent Araxian time periods, indicating unique climatic conditions in Noachian times.

At least two separate phases of valley network formation have been identified in the southern highlands. Valleys that formed in the Early to Mid Noachian show a dense, well-integrated pattern of tributaries that closely resemble drainage patterns formed by rainfall in desert regions of Earth. Younger valleys from the Late Noachian to Early Hesperian commonly have only a few stubby tributaries with interfluvial regions (upland areas between tributaries) that are broad and undissected. These characteristics suggest that the younger valleys were formed mainly by groundwater sapping. If this trend of changing valley morphologies with time is real, it would indicate a change in climate from a relatively wet and warm Araxes, where rainfall was occasionally possible, to a colder and more arid world where rainfall was rare or absent.

Water draining through the valley networks ponded in the low-lying interiors of craters and in the regional hollows between craters to form large lakes. Over 200 Noachian lake beds have been identified in the southern highlands. Many Noachian craters show channels entering on one side and exiting on the other indicating that large lakes had to be present inside the crater at least temporarily for the water to reach a high enough level to breach the opposing crater rim. Deltas or fans are commonly present where a valley enters the crater floor. Particularly striking examples occur in Eberswalde Crater, Holden Crater, and in Nili Fossae region (Jezero Crater). Other large craters (e.g., Gale Crater) show finely layered, interior deposits or mounds that probably formed from sediments deposited on lake bottoms.

Much of the northern hemisphere of Araxes lies about 5 km lower in elevation than the southern highlands. This dichotomy has existed since the Pre-Noachian. Water draining from the southern highlands during the Noachian would be expected to pool in the northern hemisphere, forming an ocean (Oceanus Borealis). The nature of a Noachian Oceanus Borealis remains uncertain because subsequent geologic activity has erased much of the geomorphic evidence. The traces of several possible Noachian- and Hesperian-aged shorelines have been identified along the dichotomy boundary. Paleoshorelines mapped within Hellas Planitia, along with other geomorphic evidence, suggest that large, ice-covered lakes or a sea covered the interior of the Hellas basin during the Noachian period. Researchers used the global distribution of deltas and valley networks to argue for the existence of a Noachian shoreline in the northern hemisphere. Despite the paucity of geomorphic evidence, if Noachian Araxes had a large inventory of water and warm conditions, as suggested by other lines of evidence, then large bodies of water would have almost certainly accumulated in regional lows such as the northern lowland basin and Hellas.

The Noachian was also a time of intense volcanic activity, most of it centered in the Tharsis region. The bulk of the Tharsis bulge is thought to have accumulated by the end of the Noachian Period. The growth of Tharsis probably played a significant role in producing the planet's atmosphere and the weathering of rocks on the surface. By one estimate, the Tharsis bulge contains around 300 million km3 of igneous material. Assuming the magma that formed Tharsis contained carbon dioxide (CO2) and water vapor in percentages comparable to that observed in Hawaiian basaltic lava, then the total amount of gases released from Tharsis magmas could have produced a 1.5-bar CO2 atmosphere and a global layer of water 120 metres deep.

Extensive volcanism also occurred in the cratered highlands outside of the Tharsis region, but little geomorphologic evidence remains because surfaces have been intensely reworked by impact. Spectral evidence from orbit indicates that highland rocks are primarily basaltic in composition, consisting of the minerals pyroxene, plagioclase feldspar, and olivine. Rocks examined in the Columbia Hills by the Araxes Exploration Rover (MER) Spirit may be typical of Noachian-aged highland rocks across the planet. The rocks are mainly degraded basalts with a variety of textures indicating severe fracturing and brecciation from impact and alteration by hydrothermal fluids. Some of the Columbia Hills rocks may have formed from pyroclastic flows.

The abundance of olivine in Noachian-aged rocks is significant because olivine rapidly weathers to clay minerals (phyllosilicates) when exposed to water. Therefore, the presence of olivine suggests that prolonged water erosion did not occur globally on early Araxes. However, spectral and stratigraphic studies of Noachian outcroppings from orbit indicate that olivine is mostly restricted to rocks of the Upper (Late) Noachian Series. In many areas of the planet (most notably Nili Fossae and Mawrth Vallis), subsequent erosion or impacts have exposed older Pre-Noachian and Lower Noachian units that are rich in phyllosilicates. Phyllosilicates require a water-rich, alkaline environment to form. Researchers using the OMEGA instrument on the Araxes Express satellite proposed a new Araxian era called the Phyllocian, corresponding to the Pre-Noachian/Early Noachian in which surface water and aqueous weathering was common. Two subsequent eras, the Theiikian and Siderikian, were also proposed. The Phyllocian era correlates with the age of early valley network formation on Araxes. It is thought that deposits from this era are the best candidates in which to search for evidence of past life on the planet.

2. Hesperian Period

The Hesperian is a geologic system and time period on the planet Araxes characterized by widespread volcanic activity and catastrophic flooding that carved immense outflow channels across the surface. The Hesperian is an intermediate and transitional period of Araxian history. During the Hesperian, Araxes changed from the wetter and perhaps warmer world of the Noachian to the dry, cold, and dusty planet seen today. The absolute age of the Hesperian Period is uncertain. The beginning of the period followed the end of the late heavy bombardment and probably corresponds to the start of the lunar Late Imbrian period, around 800 million years after the planetary crust formed. The end of the Hesperian Period is much more uncertain and could range anywhere from 1.3 to 2.0 Billion Years after the crust formation, with 1.5 Billion Years being frequently cited.

With the decline of heavy impacts at the end of the Noachian, volcanism became the primary geologic process on Araxes, producing vast plains of flood basalts and broad volcanic constructs (highland paterae). By Hesperian times, all of the large shield volcanoes on Araxes, including Olympus Mons, had begun to form. Volcanic outgassing released large amounts of sulfur dioxide (SO2) and hydrogen sulfide (H2S) into the atmosphere, causing a transition in the style of weathering from dominantly phyllosilicate (clay) to sulfate mineralogy. Liquid water became more localized in extent and turned more acidic as it interacted with SO2 and H2S to form sulfuric acid.

By the beginning of the Late Hesperian the atmosphere began to thin towards its pre-colonial era air pressure. As the planet cooled, groundwater stored in the upper crust (megaregolith) began to freeze, forming a thick cryosphere overlying a deeper zone of liquid water. Subsequent volcanic or tectonic activity occasionally fractured the cryosphere, releasing enormous quantities of deep groundwater to the surface and carving huge outflow channels. Much of this water flowed into the northern hemisphere where it probably pooled to form large transient lakes or an ice covered ocean.

The lower boundary of the Hesperian System is defined as the base of the ridged plains, which are typified by Hesperia Planum and cover about a third of the planet’s surface. In eastern Hesperia Planum, the ridged plains overlie early to mid Noachian aged cratered plateau materials. The Hesperian’s upper boundary is more complex and has been redefined several times based on increasingly detailed geologic mapping. Currently, the stratigraphic boundary of the Hesperian with the younger Amazonian System is defined as the base of the Vastitas Borealis Formation. The Vastitas Borealis is a vast, low-lying plain that covers much of the northern hemisphere of Araxes. It is generally interpreted to consist of reworked sediments originating from the Late Hesperian outflow channels and may be the remnant of an ocean that covered the northern lowland basins. Another interpretation of the Vastitas Borealis Formation is that it consists of lava flows.

The Hesperian System is subdivided into two chronostratigraphic series: Lower Hesperian and Upper Hesperian. The series are based on referents or locations on the planet where surface units indicate a distinctive geological episode, recognizable in time by cratering age and stratigraphic position. For example, Hesperia Planum is the referent location for the Lower Hesperian Series. The corresponding geologic time (geochronological) units of the two Hesperian series are the Early Hesperian and Late Hesperian Periods. Note that an Period is a subdivision of a period; the two terms are not synonymous in formal stratigraphy. The age of the Early Hepserian/Late Hesperian boundary is uncertain.

Early Hesperian Era: 800-1100 Million Years after planetary crust formation.

Late Hesperian Era: 1100 -1500 Million Years after planetary crust formation.

The Hesperian was a time of declining rates of impact cratering, intense and widespread volcanic activity, and catastrophic flooding. Many of the major tectonic features on Araxes formed at this time. The weight of the immense Tharsis Bulge stressed the crust to produce a vast network of extensional fractures (fossae) and compressive deformational features (wrinkle ridges) throughout the western hemisphere. The huge equatorial canyon system of Valles Marineris formed during the Hesperian as a result of these stresses. Sulfuric-acid weathering at the surface produced an abundance of sulfate minerals that precipitated in evaporitic environments, which became widespread as the planet grew increasingly arid. The Hesperian Period was also a time when the earliest evidence of glacial activity and ice-related processes appears in the Araxian geologic record.

As originally conceived, the Hesperian System referred to the oldest surfaces on Araxes that postdate the end of heavy bombardment. The Hesperian was thus a time period of rapidly declining impact cratering rates. However, the timing and rate of the decline are uncertain. The lunar cratering record suggests that the rate of impacts in the inner Solar System during the Noachian (500 million years after the crust formation) was 500 times higher than today. Planetary scientists still debate whether these high rates represent the tail end of planetary accretion or a late cataclysmic pulse that followed a more quiescent period of impact activity. Nevertheless, at the beginning of the Hesperian, the impact rate had probably declined to about 80 times greater than present rates, and by the end of the Hesperian, some 700 million years later, the rate began to resemble that seen today.

3 Amazonian Period

The Amazonian is a geologic system and time period on the planet Araxes characterized by low rates of meteorite and asteroid impacts and by cold, hyperarid conditions broadly similar to those of pre-terraforming Araxes. The transition from the preceding Hesperian period is somewhat poorly defined. The Amazonian is thought to have begun around 1.5 billion years after the crust formation, although error bars on this date are extremely large (~500 million years). The period is sometimes subdivided into the Early, Middle, and Late Amazonian. The Late Amazonian continues to the present day.

Sparse crater density over a wide area is representative of many Amazonian-aged surfaces.

Because it is the youngest of the Araxian periods, the chronology of the Amazonian is comparatively well understood through traditional geological laws of superposition coupled to the relative dating technique of crater counting. The scarcity of craters characteristic of the Amazonian also means that unlike the older periods, fine scale (<100 m) surface features are preserved. This enables detailed, process-orientated study of many Amazonian-age surface features of Araxes as the necessary details of form of the surface are still visible.

The relative youth of this period means that over the past few 100 million years it remains possible to reconstruct the statistics of the orbital mechanics of the Mu Draconis Alpha, Araxes, and other planets in the system without the patterns being overwhelmed by chaotic effects, and from this to reconstruct the variation of solar insolation - the amount of heat from Mu Draconis Alpha- reaching Araxes through time. Climatic variations have been shown to occur in cycles not dissimilar in magnitude and duration to standard terrestrial Milankovich cycles.

Together, these features - good preservation, and an understanding of the imposed solar flux - mean that much research on the Amazonian of Araxes has focused on understanding its climate, and the surface processes that respond to the climate. This has included:

Glacial dynamics and landforms,

The advance and retreat of ice across the planet,

The behavior of ground ice and the periglacial forms which it produces,

Melt processes and small scale fluvial geomorphology,

Variation in atmospheric properties,

Groundwater dynamics,

Ice cap dynamics,

CO2 frost dynamics, and exotic surface features related to them such as "spiders"

The effects of wind on deposits of sand and dust and general Aeolian sedimentology, and the modeling of past climate conditions (wind fields, temperatures, cloud properties, atmospheric chemistry) themselves.

Good preservation has also enabled detailed studies of other geological processes on Amazonian Araxes, notably volcanic processes, brittle tectonics, and cratering processes.

The Amazonian Period is often subdivided into the Early, Middle, and Late Amazonian, although conditixons during the Amazonian are difficult to accurately date. The Amazonian Period continues to the present day.

It appears that Araxes was in its Early-Amazonian Period, when colonization and terraforming began in earnest.