Middle Noachian
59-461: The Noachian is a geologic system and early time period on the planet Mars 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 lunar Pre-Nectarian to Early Imbrian periods of 4100 to 3700 million years ago, during the interval known as
118-422: A sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin. In the same way, the sediments or sedimentary rocks on top of the basement can be called a "cover" or "sedimentary cover". Crustal rocks are modified several times before they become basement, and these transitions alter their composition. Basement rock
177-407: A terrane was accreted to the edge of the continent. Any of this material may be folded, refolded and metamorphosed. New igneous rock may freshly intrude into the crust from underneath, or may form underplating , where the new igneous rock forms a layer on the underside of the crust. The majority of continental crust on the planet is around 1 to 3 billion years old, and it is theorised that there
236-459: A weak zone on which the harder (stronger) limestone cover was able to move over the hard basement, making the distinction between basement and cover even more pronounced. In Andean geology the basement refers to the Proterozoic , Paleozoic and early Mesozoic ( Triassic to Jurassic ) rock units as the basement to the late Mesozoic and Cenozoic Andean sequences developed following
295-456: A cold, hyperarid desert with an average atmospheric pressure less than 1% that of Earth. Liquid water is unstable and will either freeze or evaporate depending on season and location (See Water on Mars ). Reconciling the geologic evidence of river valleys and lakes with computer climate models of Noachian Mars has been a major challenge. Models that posit a thick carbon dioxide atmosphere and consequent greenhouse effect have difficulty reproducing
354-575: 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:
413-435: 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
472-603: 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,
531-512: A large scale (>100 m), Noachian surfaces are very hilly and rugged, superficially resembling the 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. (See Anseris Mons , for example.) The number-density of large impact craters is very high, with about 200 craters greater than 16 km in diameter per million km. Noachian-aged units cover 45% of
590-473: A plate of oceanic crust is subducted beneath an overriding plate of oceanic crust, as the underthrusting crust melts, it causes an upwelling of magma that can cause volcanism along the subduction front on the overriding plate. This produces an oceanic volcanic arc , like Japan . This volcanism causes metamorphism , introduces igneous intrusions , and thickens the crust by depositing additional layers of extrusive igneous rock from volcanoes. This tends to make
649-522: A relatively thin veneer, but can be more than 5 kilometres (3 mi) thick. The basement rock of the crust can be 32–48 kilometres (20–30 mi) thick or more. The basement rock can be located under layers of sedimentary rock, or be visible at the surface. Basement rock is visible, for example, at the bottom of the Grand Canyon , consisting of 1.7- to 2-billion-year-old granite ( Zoroaster Granite ) and schist ( Vishnu Schist ). The Vishnu Schist
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#1732773038063708-463: 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
767-474: Is a sequence of strata (rock layers) that were laid down together within the same corresponding geological period . The associated period is a chronological time unit , a part of the geological time scale , while the system is a unit of chronostratigraphy . Systems are unrelated to lithostratigraphy , which subdivides rock layers on their lithology . Systems are subdivisions of erathems and are themselves divided into series and stages . The systems of
826-484: 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
885-594: Is believed to be highly metamorphosed igneous rocks and shale , from basalt , mud and clay laid from volcanic eruptions, and the granite is the result of magma intrusions into the Vishnu Schist. An extensive cross section of sedimentary rocks laid down on top of it through the ages is visible as well. The basement rocks of the continental crust tend to be much older than the oceanic crust. The oceanic crust can be from 0–340 million years in age, with an average age of 64 million years. Continental crust
944-437: Is clearly necessary for a more complete understanding of Martian 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 lunar cratering record suggests that
1003-560: 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. 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
1062-472: 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
1121-495: Is older because continental crust is light and thick enough so it is not subducted, while oceanic crust is periodically subducted and replaced at subduction and oceanic rifting areas. The basement rocks are often highly metamorphosed and complex, and are usually crystalline . They may consist of many different types of rock – volcanic, intrusive igneous and metamorphic. They may also contain ophiolites , which are fragments of oceanic crust that became wedged between plates when
1180-460: 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 Mars. 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
1239-506: Is still debated, valley networks are rare in subsequent Martian 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
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#17327730380631298-570: 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)
1357-413: Is the thick foundation of ancient, and oldest, metamorphic and igneous rock that forms the crust of continents , often in the form of granite . Basement rock is contrasted to overlying sedimentary rocks which are laid down on top of the basement rocks after the continent was formed, such as sandstone and limestone . The sedimentary rocks which may be deposited on top of the basement usually form
1416-525: The Late Heavy Bombardment . Many of the large impact basins on the Moon and Mars formed at this time. The Noachian Period is roughly equivalent to the Earth's Hadean and early Archean eons when Earth's first life forms likely arose. Noachian-aged terrains on Mars are prime spacecraft landing sites to search for fossil evidence of life . During the Noachian, the atmosphere of Mars
1475-602: The Ordovician system was added in 1879. The Cenozoic has seen more recent revisions by the International Commission on Stratigraphy . It has been divided into three systems with the Paleogene and Neogene replacing the former Tertiary System though the succeeding Quaternary remains. The one-time system names of Paleocene , Eocene , Oligocene , Miocene and Pliocene are now series within
1534-648: The Phanerozoic were defined during the 19th century, beginning with the Cretaceous (by Belgian geologist Jean d'Omalius d'Halloy in the Paris Basin ) and the Carboniferous (by British geologists William Conybeare and William Phillips in 1822). The Paleozoic and Mesozoic were divided into the currently used systems before the second half of the 19th century, except for a minor revision when
1593-535: The geomorphic evidence. The traces of several possible Noachian- and Hesperian-aged shorelines have been identified along the dichotomy boundary, but this evidence has been challenged. 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. In 2010, researchers used
1652-457: The lunar maria . These ridged plains form the base of the younger Hesperian System (pictured right). 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 formation of the crust 4500 million years ago. However, work by Herbert Frey and colleagues at NASA's Goddard Spaceflight Center using Mars Orbital Laser Altimeter (MOLA) data indicates that
1711-773: The minerals pyroxene , plagioclase feldspar , and olivine . Rocks examined in the Columbia Hills by the Mars 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
1770-495: The Earth's continents being accreted into one giant supercontinent . Most continents, such as Asia, Africa and Europe, include several continental cratons, as they were formed by the accretion of many smaller continents. In European geology , the basement generally refers to rocks older than the Variscan orogeny . On top of this older basement Permian evaporites and Mesozoic limestones were deposited. The evaporites formed
1829-491: 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 Mars, where rainfall
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1888-714: The Martian 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 ). Epochs: 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
1947-502: The Paleogene and Neogene. Another recent development is the official division of the Proterozoic into systems, which was decided in 2004. Basement (geology) In geology , basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The basement rocks lie below
2006-631: 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 Noachian System is the Noachian Period. Rock or surface units of the Noachian System were formed or deposited during the Noachian Period. System and Period are not interchangeable terms in formal stratigraphic nomenclature, although they are frequently confused in popular literature. A system
2065-574: 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 Mars. It is thought that deposits from this era are the best candidates in which to search for evidence of past life on the planet. System (stratigraphy) A system in stratigraphy
2124-451: The atmosphere. Weathering of surface rocks produced a diversity of clay minerals ( phyllosilicates ) that formed under chemical conditions conducive to microbial life . Although there is abundant geologic evidence for surface water early in Mars history, the nature and timing of the climate conditions under which that water occurred is a subject of vigorous scientific debate. Today Mars is
2183-461: 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 Mars’ early atmosphere through impact erosion. By analogy with the Moon, frequent impacts produced a zone of fractured bedrock and breccias in the upper crust called the megaregolith . The high porosity and permeability of
2242-416: The crust thicker and less dense, making it immune to subduction. Oceanic crust can be subducted, while continental crust cannot. Eventually, the subduction of the underthrusting oceanic crust can bring the volcanic arc close to a continent, with which it may collide. When this happens, instead of being subducted, it is accreted to the edge of the continent and becomes part of it. Thin strips or fragments of
2301-993: 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
2360-511: The edge of the continent. There are exceptions, however, such as exotic terranes . Exotic terranes are pieces of other continents that have broken off from their original parent continent and have become accreted to a different continent. Continents can consist of several continental cratons – blocks of crust built around an initial original core of continents – that gradually grew and expanded as additional newly created terranes were added to their edges. For instance, Pangea consisted of most of
2419-420: The fluvial features seen today. Other researchers argue for a semiarid early Mars with at least transient periods of rainfall warmed by a carbon dioxide-hydrogen atmosphere. Causes of the warming periods remain unclear but may be due to large impacts, volcanic eruptions, or orbital forcing . In any case it seems probable that the climate throughout the Noachian was not uniformly warm and wet. In particular, much of
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2478-432: 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 Mars 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
2537-451: The higher mean temperatures necessary for abundant liquid water. This is partly because Mars receives less than half the solar radiation that Earth does and because the sun during the Noachian was only about 75% as bright as it is today. As a consequence, some researchers now favor an overall Noachian climate that was “cold and icy” punctuated by brief (hundreds to thousands of years) climate excursions warm enough to melt surface ice and produce
2596-731: The magma that formed Tharsis contained carbon dioxide (CO 2 ) 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 CO 2 atmosphere and a global layer of water 120 m 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
2655-487: The megaregolith permitted the deep infiltration of groundwater . Impact-generated heat reacting with the groundwater produced long-lived hydrothermal systems that could have been exploited by thermophilic microorganisms , if any existed. Computer models of heat and fluid transport in the ancient Martian 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
2714-717: 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 Epochs . Note that an epoch is a subdivision of a period; the two terms are not synonymous in formal stratigraphy. Stratigraphic terms are often confusing to geologists and non-geologists alike. One way to sort through
2773-441: The northern hemisphere of Mars 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). Unfortunately, the existence and nature of a Noachian ocean remains uncertain because subsequent geologic activity has erased much of
2832-738: The onset of subduction along the western margin of the South American Plate . When discussing the Trans-Mexican Volcanic Belt of Mexico the basement include Proterozoic, Paleozoic and Mesozoic age rocks for the Oaxaquia, the Mixteco and the Guerrero terranes respectively. The term basement is used mostly in disciplines of geology like basin geology , sedimentology and petroleum geology in which
2891-672: The other. This indicates 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
2950-570: 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. In 2006, researchers using the OMEGA instrument on the Mars Express spacecraft proposed a new Martian era called the Phyllocian, corresponding to
3009-515: The rate of impacts in the Inner Solar System 4000 million years ago was 500 times higher than today. During the Noachian, about one 100-km diameter crater formed on Mars 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
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#17327730380633068-592: The river- and lake-forming activity appears to have occurred over a relatively short interval at the end of the Noachian and extending into the early Hesperian . The Noachian System and Period is named after Noachis Terra (lit. "Land of Noah "), a heavily cratered highland region west of the Hellas basin. The type area of the Noachian System is in the Noachis quadrangle (MC-27) around 40°S 340°W / 40°S 340°W / -40; -340 . At
3127-450: The southern highlands of Mars 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. He suggests that the Hellas impact should mark the base of the Noachian System. If Frey is correct, then much of the bedrock in the Martian highlands is pre-Noachian in age, dating back to over 4100 million years ago. The Noachian System
3186-414: The underthrusting oceanic plate may also remain attached to the edge of the continent so that they are wedged and tilted between the converging plates, creating ophiolites . In this manner, continents can grow over time as new terranes are accreted to their edges, and so continents can be composed of a complex quilt of terranes of varying ages. As such, the basement rock can become younger going closer to
3245-474: 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 km of igneous material. Assuming
3304-572: Was at least one period of rapid expansion and accretion to the continents during the Precambrian. Much of the basement rock may have originally been oceanic crust, but it was highly metamorphosed and converted into continental crust . It is possible for oceanic crust to be subducted down into the Earth's mantle , at subduction fronts, where oceanic crust is being pushed down into the mantle by an overriding plate of oceanic or continental crust. When
3363-405: Was denser than it is today, and the climate possibly warm enough (at least episodically) to allow rainfall. Large lakes and rivers were present in the southern hemisphere, and an ocean may have 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
3422-590: 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 Mars 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)
3481-517: 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, some as large as Lake Baikal or the Caspian Sea on Earth. Many Noachian craters show channels entering on one side and exiting on
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