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30-465: During the Pre-Noachian period, the northern hemisphere of Mars developed lowlands , which may have served as reservoirs for ancient Martian water during subsequent epochs. These lowlands likely formed through lava erosion caused by extensive volcanic activity, as the Pre-Noachian period experienced the highest level of volcanic activity among all Martian epochs. The atmosphere of Mars during

60-1040: A riffle and pool structure and cooler water temperatures. Rivers with a course that drops in elevation very slowly will have slower water flow and lower force. This in turn produces the other characteristics of a lowland river—a meandering course lacking rapids , a river bed dominated by fine sediments and higher water temperatures. Lowland rivers tend to carry more suspended sediment and organic matter as well, but some lowland rivers have periods of high water clarity in seasonal low-flow periods. The generally clear, cool, fast-flowing waters and bedrock and coarse sediment beds of upland rivers encourage fish species with limited temperature tolerances, high oxygen needs, strong swimming ability and specialised reproductive strategies to prevent eggs or larvae being swept away. These characteristics also encourage invertebrate species with limited temperature tolerances, high oxygen needs and ecologies revolving around coarse sediments and interstices or "gaps" between those coarse sediments. The term "upland"

90-505: A stratum ( pl. : strata ) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as either bedding surfaces or bedding planes . Prior to the publication of the International Stratigraphic Guide, older publications have defined a stratum as being either equivalent to

120-575: A crater ejecta deposit, lava flow, or any surface that can be represented in three dimensions as a discrete stratum bound above or below by adjacent units (illustrated right). Using principles such as superpositioning (illustrated left), cross-cutting relationships , and the relationship of impact crater density to age, geologists can place the units into a relative age sequence from oldest to youngest. Units of similar age are grouped globally into larger, time-stratigraphic ( chronostratigraphic ) units, called systems . For Mars, four systems are defined:

150-436: A few millimeters to several meters or more. A band may represent a specific mode of deposition : river silt , beach sand , coal swamp , sand dune , lava bed, etc. In the study of rock and sediment strata, geologists have recognized a number of different types of strata, including bed , flow , band , and key bed . A bed is a single stratum that is lithologically distinguishable from other layers above and below it. In

180-435: A geologic period represents the time interval over which the strata of a system were deposited, including any unknown amounts of time present in gaps. Periods are measured in years, determined by radioactive dating . On Mars, radiometric ages are not available except from Martian meteorites whose provenance and stratigraphic context are unknown. Instead, absolute ages on Mars are determined by impact crater density, which

210-603: A given system are apt to contain gaps ( unconformities ) analogous to missing pages from a book. In some places, rocks from the system are absent entirely due to nondeposition or later erosion. For example, rocks of the Cretaceous System are absent throughout much of the eastern central interior of the United States. However, the time interval of the Cretaceous (Cretaceous Period) still occurred there. Thus,

240-621: A single bed or composed of a number of beds; as a layer greater than 1 cm in thickness and constituting a part of a bed; or a general term that includes both bed and lamina . Related terms are substrate and substratum (pl. substrata ), a stratum underlying another stratum. Typically, a stratum is generally one of a number of parallel layers that lie one upon another to form enormous thicknesses of strata. The bedding surfaces (bedding planes) that separate strata represent episodic breaks in deposition associated either with periodic erosion , cessation of deposition, or some combination of

270-727: Is also used in wetland ecology , where "upland" plants indicate an area that is not a wetland. The generally more turbid , warm, slow-flowing waters and fine sediment beds of lowland rivers encourage fish species with broad temperature tolerances and greater tolerances to low oxygen levels, and life history and breeding strategies adapted to these and other traits of lowland rivers. These characteristics also encourage invertebrate species with broad temperature tolerances and greater tolerances to low oxygen levels and ecologies revolving around fine sediments or alternative habitats such as submerged woody debris ("snags") or submergent macrophytes ("water weed"). Lowland alluvial plains form when there

300-484: Is an idealized stratigraphic column based on the physical rock record of a type area (type section) correlated with rocks sections from many different locations planetwide. A system is bound above and below by strata with distinctly different characteristics (on Earth, usually index fossils ) that indicate dramatic (often abrupt) changes in the dominant fauna or environmental conditions. (See Cretaceous–Paleogene boundary as example.) At any location, rock sections in

330-466: Is clearly necessary for a more complete understanding of Martian history and chronology. During the Pre-Noachian period, Mars experienced significant geological and environmental dynamics. Intense volcanic activity sculpted the planet's surface through widespread eruptions, while impact cratering events left numerous craters across the Martian landscape. The atmosphere during this era was denser than it

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360-407: Is defined by the presence of ancient cratered terrains, volcanic constructs, and impact ejecta deposits dating back to the earliest stages of Martian geological development. While the precise location of this boundary may vary depending on geological context and criteria used for its definition, it marks the beginning of Mars’ geological history as understood by scientists. In the Pre-Noachian period,

390-596: Is deposition of sediment over a long period of time by one or more rivers coming from highland regions, and then are deposited in lowland regions for long periods of time. Examples include American Bottom , a flood plain of the Mississippi River in Southern Illinois, Bois Brule Bottom , and Bottomland hardwood forest a deciduous hardwood forest found in broad lowland floodplains of the United States. Stratum In geology and related fields,

420-453: Is frequently colored by sediment and organic matter. These classifications overlap with the geological definitions of "upland" and "lowland". In geology an "upland" is generally considered to be land that is at a higher elevation than the alluvial plain or stream terrace , which are considered to be "lowlands". The term "bottomland" refers to low-lying alluvial land near a river. Much freshwater fish and invertebrate communities around

450-519: Is heavily dependent upon models of crater formation over time. Accordingly, the beginning and end dates for Martian periods are uncertain, especially for the Hesperian/Amazonian boundary, which may be in error by a factor of 2 or 3. The lower boundary of the Pre-Noachian period on Mars is characterized by the emergence of significant geological activity and the initial shaping of the planet's surface during its early history. This boundary

480-472: Is large enough to be shown on a map. Mappers use a stratigraphic approach pioneered in the early 1960s for photogeologic studies of the Moon . Although based on surface characteristics, a surface unit is not the surface itself or group of landforms . It is an inferred geologic unit (e.g., formation ) representing a sheetlike, wedgelike, or tabular body of rock that underlies the surface. A surface unit may be

510-685: Is named after Noachis Terra , a region of highlands west of the Hellas Planitia basin , and the pre comes from the word meaning before. (See Description and name origin on the Misplaced Pages page for the Noachian era on Mars for more information) Martian time periods are based on geologic mapping of surface units from spacecraft images . A surface unit is a terrain with a distinct texture, color, albedo , spectral property, or set of landforms that distinguish it from other surface units and

540-433: Is not the sole determinant of whether a river is upland or lowland. Arguably the most important determinants are those of stream power and stream gradient . Rivers with a course that drops rapidly in elevation will have faster water flow and higher stream power or "force of water". This in turn produces the other characteristics of an upland river—an incised course , a river bed dominated by bedrock and coarse sediments,

570-474: Is today, likely containing higher concentrations of carbon dioxide and other gases, potentially contributing to a greenhouse effect . This atmospheric composition may have facilitated conditions conducive to the presence of liquid water on the surface , with evidence suggesting the existence of water bodies such as lakes , rivers , and possibly even oceans . Geological features such as valleys , channels , and basins formed during this period further support

600-574: The Caspian Depression lie below sea level. Uplands areas tend to spike into valleys and mountains , forming mountain ranges while lowland areas tend to be uniformly flat, although both can vary such as the Mongolian Plateau . Upland habitats are cold, clear and rocky whose rivers are fast-flowing in mountainous areas; lowland habitats are warm with slow-flowing rivers found in relatively flat lowland areas, with water that

630-787: The Pre-Noachian Noachian, Hesperian, and Amazonian. Geologic units lying below (older than) the Noachian are informally designated Pre-Noachian. The geologic time ( geochronologic ) equivalent of the Pre-Noachian System is the Pre-Noachian Period. Rock or surface units of the Pre-Noachian System were formed or deposited during the Pre-Noachian Period. System and Period are not interchangeable terms in formal stratigraphic nomenclature, although they are frequently confused in popular literature. A system

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660-477: The Pre-Noachian period was denser than it is today, containing higher concentrations of carbon dioxide from volcanic and meteorite outgassing . This may have led to a greenhouse effect on Mars and the formation of various minerals, including silicates , iron oxide , sulfates , carbonates , clays , and hydrates , due to intense heat. Meteorite outgassing is believed to have caused water vapor to condense into Mars' atmosphere, eventually precipitating onto

690-473: The classification hierarchy of sedimentary lithostratigraphic units, a bed is the smallest formal unit. However, only beds that are distinctive enough to be useful for stratigraphic correlation and geologic mapping are customarily given formal names and considered formal lithostratigraphic units. The volcanic equivalent of a bed, a flow, is a discrete extrusive volcanic stratum or body distinguishable by texture, composition, or other objective criteria. As in case of

720-993: The difficulty is by the following example: You can easily go to Cincinnati, Ohio and visit a rock outcrop in the Upper Ordovician Series of the Ordovician System. You can even collect a fossil trilobite there. However, you cannot visit the Late Ordovician Epoch in the Ordovician Period and collect an actual trilobite. The Earth-based scheme of formal stratigraphic nomenclature has been successfully applied to Mars for several decades now but has numerous flaws. The scheme will no doubt become refined or replaced as more and better data become available. (See mineralogical timeline below as example of alternative.) Obtaining radiometric ages on samples from identified surface units

750-693: The eastern region of Mars featured ridged plains overlaying early to mid-Noachian aged cratered plateau materials. This period marked a significant phase in Mars’ geological history, preceding the Noachian era characterized by its own distinct geological features and processes. The Pre-Noachian System is subdivided into two chronostratigraphic series : Lower Pre-Noachian and Upper Pre-Noachian. These series are delineated based on specific references or locations on Mars where surface units indicate distinctive geological episodes, identifiable by cratering age and stratigraphic position. For example, Hesperia Planum serves as

780-591: The notion of liquid water on ancient Mars. Lowlands Upland and lowland are conditional descriptions of a plain based on elevation above sea level . In studies of the ecology of freshwater rivers , habitats are classified as upland or lowland. Upland and lowland are portions of a plain that are conditionally categorized by their elevation above the sea level . Lowlands are usually no higher than 200 m (660 ft), while uplands are somewhere around 200 m (660 ft) to 500 m (1,600 ft). On unusual occasions, certain lowlands such as

810-819: The referent location for the Lower Pre-Noachian Series. The corresponding geologic time units for the two Pre-Noachian series are the Early Pre-Noachian and Late Pre-Noachian Epochs . It's important to note that an epoch is a subdivision of a period, and the terms are not synonymous in formal stratigraphy. The age of the Early Pre-Noachian/Late Pre-Noachian boundary remains uncertain, with estimates ranging from 4500 to 4100 million years ago based on crater counts. Stratigraphic terms are often confusing to geologists and non-geologists alike. One way to sort through

840-438: The surface and forming oceans during subsequent epochs. Over time, gases trapped by Mars' gravity during the Pre-Noachian period have gradually escaped into space as the planet cooled. During this era, Mars possessed a distinctive magnetic field , indicating an active core . As magma cooled in the planet's lower layers, it generated metals necessary for the formation of the magnetic field. The Pre-Noachian System and Period

870-497: The two. Stacked together with other strata, individual stratum can form composite stratigraphic units that can extend over hundreds of thousands of square kilometers of the Earth 's surface. Individual stratum can cover similarly large areas. Strata are typically seen as bands of different colored or differently structured material exposed in cliffs , road cuts, quarries , and river banks. Individual bands may vary in thickness from

900-531: The world show a pattern of specialization into upland or lowland river habitats. Classifying rivers and streams as upland or lowland is important in freshwater ecology , as the two types of river habitat are very different, and usually support very different populations of fish and invertebrate species. In freshwater ecology, upland rivers and streams are the fast-flowing rivers and streams that drain elevated or mountainous country, often onto broad alluvial plains (where they become lowland rivers). However, elevation

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