Land and Sea

7/31/2019 Land and Sea

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Land and Sea

There are many theory of formation of the Earth which outlines how it hascome into existence. The geological history of Earth follows the major eventsin Earth's past based on the geologic time scale, a system of chronologicalmeasurement based on the study of the planet's rock layers (stratigraphy).Earth formed about 4.54 billion years agoby accretion from the solar nebula, a

disk-shaped mass of dust and gas left over from the formation of the Sun,which also created the rest of the Solar System.

Earth was initially molten due to extreme volcanic activities and frequentcollisions with other bodies. Eventually, the outer layer of the planet cooled toform a solid crust when water began accumulating in the atmosphere.Outgassing and volcanic activity produced the primordial atmosphere.Condensing water vapor, augmented by ice delivered from comets, producedthe oceans.

As the surface continually reshaped itself over hundreds of millions of years,continents formed and broke apart. They migrated across the surface,

occasionally combining to form a supercontinent. Roughly 750 Ma the earliest-known supercontinent Rodinia, began to break apart. The continents laterrecombined to form Pannotia, 600540 Ma,[5] then finally Pangaea, whichbroke apart 180 Ma.

The late Paleozoic-early Mesozoic supercontinent of Pangaea completed its

breakup into present day continents by the end of the Mesozoic era, the continents

had drifted into nearly their present form. Laurasia became North and Eurasia,

while Gondwana split into South America, Africa, Australia, Antarctica and

the Indian subcontinent, which collided with the Asian plate. This impact gave rise

to the Himalayas. The Tethys Sea, which had separated the northern continents

from Africa and India, began to close up, forming the Mediterranean Sea.
http://en.wikipedia.org/wiki/Geological_history_of_Earth#cite_note-ICS2008-4http://en.wikipedia.org/wiki/Geological_history_of_Earth#cite_note-ICS2008-4


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Rodina

Pannotia

Pangaea

Plate tectonics


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Plate tectonics is a scientific theory that describes the large scale motionsof Earth's lithosphere. The theory builds on the concepts of continental drift,developed during the first decades of the 20th century, and accepted by themajority of the geo-scientific community when the concepts of seafloorspreading were developed in the late 1950s and early 1960s.

The lithosphere is broken up into tectonic plates. In the case of the Earth,there are currently seven or eight major (depending on how they are defined)and many minor plates. The lithospheric plates ride on the asthenosphere.These plates move in relation to one another at one of three types of plateboundaries: convergent or collisional boundaries; divergent boundaries, alsocalled spreading centers; andconservative transform boundaries. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries.The lateral relative movement of the plates typically varies from 0100 mmannually.

The tectonic plates are composed of two types of lithosphere: thickercontinental and thin oceanic. The upper part is called the crust, again of two

types (continental and oceanic). This means that a plate can be of one type, orof both types. One of the main points the theory proposes is that the amountof surface of the (continental and oceanic) plates that disappears in themantle along the convergent boundaries by subduction is more or less inequilibrium with the new (oceanic) crust that is formed along the divergentmargins by seafloor spreading. This is also referred to as the conveyor beltprinciple. In this way, the total surface of the globe remains the same. This isin contrast with earlier theories advocated before the PlateTectonics paradigm, as it is sometimes called, became the main scientificmodel, theories that proposed gradual shrinking (contraction) or gradualexpansion of the globe, and that still exist in science as alternative models.

Earth's lithosphere

In the Earth the lithosphere includes the crust and the uppermost mantle,which constitute the hard and rigid outer layer of the Earth. Thelithosphere is underlain by the asthenosphere, the weaker, hotter, anddeeper part of the upper mantle. The boundary between the lithosphereand the underlying asthenosphere is defined by a difference in responseto stress: the lithosphere remains rigid for very long periods of geologictime in which it deforms elastically and through brittle failure, while theasthenosphere deforms viscously and accommodates strain throughplastic deformation. The lithosphere is broken intotectonic plates. Theuppermost part of the lithosphere that chemically reacts totheatmosphere,hydrosphereandbiospherethrough thesoil formingprocessis called thepedosphere.


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The concept of the lithosphere as Earths strong outer layer was developedbyJoseph Barrell, who wrote a series of papers introducing the concept.The concept was based on the presence of significant gravity anomaliesover continental crust, from which he inferred that there must exist astrong upper layer (which he called the lithosphere) above a weaker layerwhich could flow (which he called the asthenosphere). These ideas wereexpanded by Harvard geologistReginald Aldworth Dalyin 1940 with his

seminal work "Strength and Structure of the Earth"and have beenbroadly accepted by geologists and geophysicists. Although these ideasabout lithosphere and asthenosphere were developed long beforeplatetectonic theorywas articulated in the 1960s, the concepts that a stronglithosphere exists and that this rests on a weak asthenosphere areessential to that theory.

There are two types of lithosphere:

Oceanic lithosphere, which is associated withOceanic crustand exists in theocean basins

Continental lithosphere, which is associated withContinental crustThe thickness of the lithosphere is considered to be the depth to the isotherm

associated with the transition between brittle and viscous behavior.Thetemperature at which olivinebegins to deform viscously (~1000 C) isoften used to set this isotherm because olivine is generally the weakestmineral in the upper mantle. Oceanic lithosphere is typically about 50100 km thick (but beneath themid-ocean ridgesis no thicker than thecrust), while continental lithosphere has a range in thickness from about40 km to perhaps 200 km; the upper ~30 to ~50 km of typicalcontinental lithosphere is crust. The mantle part of the lithosphereconsists largely of peridotite. The crust is distinguished from the uppermantle by the change in chemical composition that takes place attheMoho discontinuity.

Oceanic lithosphere

Oceanic lithosphere consists mainly ofmaficcrust andultramaficmantle(peridotite) and is denser than continental lithosphere, for which themantle is associated with crust made offelsicrocks. Oceanic lithospherethickens as it ages and moves away from the mid-ocean ridge. Thisthickening occurs by conductive cooling, which converts hotasthenosphere into lithospheric mantle and causes the oceanic

lithosphere to become increasingly thick and dense with age. Thethickness of the mantle part of the oceanic lithosphere can beapproximated as a thermal boundary layer that thickens as the squareroot of time.

Here,his the thickness of the oceanic mantle lithosphere,is the thermaldiffusivity (approximately 106m2/s), andtis time.


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Oceanic lithosphere is less dense than asthenosphere for a few tens of millionsof years but after this becomes increasingly denser than asthenosphere.This is because the chemically-differentiated oceanic crust is lighter thanasthenosphere, butthermal contractionof the mantle lithosphere makesit denser than the asthenosphere. The gravitational instability of matureoceanic lithosphere has the effect that atsubduction zones, oceaniclithosphere invariably sinks underneath the overriding lithosphere, which

can be oceanic or continental. New oceanic lithosphere is constantlybeing produced at mid-ocean ridges and is recycled back to the mantle atsubduction zones. As a result, oceanic lithosphere is much younger thancontinental lithosphere: the oldest oceanic lithosphere is about 170million years old, while parts of the continental lithosphere are billions ofyears old. The oldest parts of continental lithosphere underlie cratons,and the mantle lithosphere there is thicker and less dense than typical;the relatively low density of such mantle "roots of cratons" helps tostabilize these regions.

Subducted lithosphere

Geophysical studies in the early 21st century posit that large pieces of thelithosphere have been subducted into the mantle as deep as 2900 km tonear the core-mantle boundary,while others "float" in the uppermantle,while some stick down into the mantle as far as 400 km butremain "attached" to the continental plate above,similar to the extent ofthe "tectosphere" proposed by Jordan in 1988.

Tectonic plates

Tectonic plates are pieces of the Earth'scrustand uppermost mantle, togetherreferred to as thelithosphere. The plates are around 100 km (62 mi) thickand consist of two principal types of material:oceanic crust(alsocalledsimafromsiliconandmagnesium) andcontinental crust(sialfromsilicon andaluminum). The composition of the two types of crust differsmarkedly, withbasalticrocks ("mafic") dominating oceanic crust, whilecontinental crust consists principally of lowerdensitygraniticrocks("felsic").

Primary plates

These seven plates comprise the bulk of the seven continents and the PacificOcean.


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African Plate

Antarctic Plate

Eurasian Plate

Indo-Australian Plate

North American Plate

Pacific Plate

South American Plate

Secondary plates

These smaller plates are generally shown on major plate maps, but with theexception of the Arabian and Indian plates do not comprise significant landarea.

Arabian Plate

Caribbean Plate

Cocos Plate Indian Plate

Juan de Fuca Plate

Nazca Plate

Philippine Sea Plate

Scotia Plate

Tertiary plates

Tertiary plates are grouped with the major plate that they would otherwise be

shown as part of on a major plate map. Mostly these are tiny micro-plates,although in the case of the Nubian-Somalian and Australian-Capricorn-Indianplates these are major plates that are drifting apart. Some models identifymore minor plates within current orogens like the Apulian, Explorer, Gorda,and Philippine Mobile Belt plates. The remainders of the tertiary plates are thedwindling remains of much larger ancient plates. There may or may not bescientific consensus as to whether a tertiary plate is a separate plate yet, isstill a separate plate, or should be considered a separate plate, thus newresearch could change this list.


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Sea

A sea generally refers to a large body of salt water, but the term is used inother contexts as well. Most commonly, it means a large expanse of salinewater connected with an ocean, and is commonly used as a synonym

for ocean.It is also used sometimes to describe a large saline lake that lacks anatural outlet, such as the Caspian Sea

The Earth's global ocean is the largest known surface ocean. Approximately71% of the planet's surface (~3.6108 km2) is covered by saline water that iscustomarily divided into several principal oceans and smaller seas. It is theprincipal component of Earth's hydrosphere which is integral to all known life,forms part of the carbon cycle and influences climate and weather patterns.The total volume is approximately 1.3 billion cubic kilometers (310 million cumi) with an average depth of 3,790 meters (12,430 ft). It is the habitat of230,000 species known to science, however much of the oceans depth remain

unexplored and it is estimated that over 2 million marine species may exist.The origin of Earth's oceans is still unknown though they are believed to havefirst appeared in the Hadean period and may have been the point of origin forthe emergence of life according to many theories of Abiogenesis.

Earth's surface ocean

Though generally described as several 'separate' oceans, these waterscomprise one global, interconnected body of salt water sometimesreferred to as theWorld Oceanor global ocean. This concept of acontinuous body of water with relatively free interchange among its partsis of fundamental importance tooceanography. The major oceanic

divisions are defined in part by thecontinents, variousarchipelagos, andother criteria.

These divisions are (in descending order of size):

Pacific Ocean, which separates Asia and Australia from the Americas

Atlantic Ocean, which separates the Americas from Europe and Africa

Indian Ocean, which washes upon southern Asia and separates Africaand Australia

Southern Ocean, sometimes considered an extension of the Pacific,Atlantic and Indian Oceans, which encircles Antarctica.

Arctic Ocean, sometimes considered a sea of the Atlantic, which coversmuch of the Arctic and washes upon northern North America and Eurasia.

The Pacific and Atlantic may be further subdivided by the equator intonorthern and southern portions. Smaller regions of the oceans arecalled seas, gulfs, bays, straits and other names.

Geology


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Geologically, Earth's ocean is the area of oceanic crust covered by water.Oceanic crust is the thin layer of solidified volcanic basalt that covers themantle. The ocean floor spreads from mid-ocean ridges wheretwo plates adjoin. Where two plates move towards each other, oneplate subducts under another plate (oceanic or continental) leading toan oceanic trench.

Continental crust is thicker but less dense. From this perspective, the earthhas three oceans: the World Ocean, the Caspian Seaand Black Sea. The lattertwo were formed by the collision of Cimmeria with Laurasia.

The Mediterranean Sea is at times a discrete ocean, because tectonic platemovement has repeatedly broken its connection to the World Ocean throughthe Strait of Gibraltar. The Black Sea is connected to the Mediterraneanthrough the Bosporus, but the Bosporus is a natural canal cut throughcontinental rock some 7,000 years ago, rather than a piece of oceanic seafloor like the Strait of Gibraltar.

Despite their names, smaller landlocked bodies of saltwater thatare notconnected with the World Ocean, such as the Aral Sea, areactually salt lakes.

Origin

There are several acknowledged theories as to how the world's oceans wereformed over the past 4.4 billion years.

Some of the most likely contributory factors to the origin of the oceans are asfollows:

The cooling of the primordial Earth to the point wherethe outgassed volatile components were held in an atmosphere ofsufficient pressure for the stabilization and retention of liquid water.

Comets, trans-Neptunian objects or water-rich meteorites (protoplanets)from the outer reaches of the main asteroid belt colliding with the Earthmay have brought water to the world's oceans. Measurements of the ratioof the hydrogen isotopes deuterium and protium point to asteroids, sincesimilar percentage impurities in carbon-rich chondrites were found tooceanic water, whereas previous measurement of the isotopes'concentrations in comets and trans-Neptunian objects correspond onlyslightly to water on the earth.

Biochemically through mineralization and photosynthesis. Gradual leakage of water stored in hydrous minerals of theEarth's rocks.

Photolysis: radiation can break down chemical bonds on the surface

The ocean and life


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The ocean has a significant effect on the biosphere. Oceanic evaporation, as aphase of the water cycle, is the source of most rainfall, and oceantemperatures determine climate and wind patterns that affect life onland. Life within the ocean evolved 3 billion years prior to life on land. Both thedepth and distance from shore strongly influence the amount and kindsof plants and animals that live there.

Physical propertiesThe area of the World Ocean is 361 million square kilometres (139 millionsquare miles) its volume is approximately 1.3 billion cubic kilometres (310million cu mi). This can be thought of as a cube of water with an edge lengthof 1,111 kilometres (690 mi). Its average depth is 3,790 metres (12,430 ft),and its maximum depth is 10,923 metres (6.787 mi) nearly half of the world'smarine waters are over 3,000 metres (9,800 ft) deep. The vast expanses ofdeep ocean (below 200 metres (660 ft)) cover about 66% of the Earth'ssurface. This does not include seas not connected to the World Ocean, such asthe Caspian Sea.

The total mass of the hydrosphere is about 1,400,000,000,000,000,000 metrictons (1.51018 short tons) or 1.41021 kg, which is about 0.023 percent of theEarth's total mass. Less than 3 percent is freshwater; the rest is saltwater,mostly in the ocean. The bluish color of the ocean is a composite of severalcontributing agents. Prominent contributors include dissolved organic matterand chlorophyll.

Regions and depths

Oceanographers divide the ocean into regions depending on physical andbiological conditions of these areas. The pelagic zone includes all open ocean

regions, and can be divided into further regions categorized by depth and lightabundance. The photic zone covers the oceans from surface level to 200metres down. This is the region where photosynthesis can occur and thereforeis the most bio diverse. Since plants require photosynthesis, life found deeperthan this must either rely on material sinking from above or find anotherenergy source; hydrothermal vents are the primary option in what is known asthe aphotic zone (depths exceeding 200 m). The pelagic part of the photiczone is known as the epipelagic. The pelagic part of the aphotic zone can befurther divided into regions that succeed each other vertically according totemperature.

The mesopelagic is the uppermost region. Its lowermost boundary is ata thermocline of 12 C (54 F), which, in the tropics generally lies at 7001,000metres (2,3003,300 ft). Next is the bathypelagic lying between 10 and 4 C(50 and 39 F), typically between 7001,000 metres (2,3003,300 ft) and2,0004,000 metres (6,60013,000 ft) Lying along the top of the abyssalplain is the abyssalpelagic, whose lower boundary lies at about 6,000 metres(20,000 ft). The last zone includes the deep trenches, and is known as


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the hadalpelagic. This lies between 6,00011,000 metres (20,00036,000 ft)and is the deepest oceanic zone.

Along with pelagic aphotic zones there are also benthic aphotic zones. Thesecorrespond to the three deepest zones of the deep-sea. The bathyalzone covers the continental slope down to about 4,000 metres (13,000 ft). Theabyssal zone covers the abyssal plains between 4,000 and 6,000 m. Lastly,the hadal zone corresponds to the hadalpelagic zone which is found in theoceanic trenches.

The pelagic zone can also be split into two sub regions, the neritic zone andthe oceanic zone. The neritic encompasses the water mass directly abovethe continental shelves, while the oceanic zone includes all the completelyopen water. In contrast, the littoral zone covers the region between low andhigh tide and represents the transitional area between marine and terrestrialconditions. It is also known as the intertidal zone because it is the area wheretide level affects the conditions of the region.

Ocean waves

In fluid dynamics, wind waves or, more precisely, wind-generated

waves are surface waves that occur on the freesurface of oceans, seas, lakes, rivers, and canals or even on small puddles andponds. They usually result from the wind blowing over a vast enough stretch offluid surface. Waves in the oceans can travel thousands of miles beforereaching land. Wind waves range in size from small ripples to huge waves over30 meters high .
http://en.wikipedia.org/wiki/File:Oceanic_divisions.svg


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When directly being generated and affected by the local winds, a wind wavesystem is called a wind sea. After the wind ceases to blow, wind waves arecalled swell. Or, more generally, a swell consists of wind generated waves thatare notor are hardlyaffected by the local wind at that time. They havebeen generated elsewhere, or some time ago. Wind waves in the ocean arecalled ocean surface waves.

Types of wind waves

Three different types of wind waves develop over time:

Capillary waves, or ripples

Seas

Swells

Ripples appear on smooth water when the wind blows, but will die quickly if

the wind stops. The restoring force that allows them to propagate is surfacetension. Seas are the larger-scale, often irregular motions that form undersustained winds. They tend to last much longer, even after the wind has died,and the restoring force that allows them to persist is gravity. As seaspropagate away from their area of origin, they naturally separate according totheir direction and wavelength. The regular wave motions formed in this wayare known as swells.

In the case of the Draupner wave, its 25 m (82 ft) height was 2.2 timesthe significant wave height. Such waves are distinct from tides, caused bythe Moon and Sun's gravitational pull, tsunamis that are caused by

underwater earthquakes or landslides, and waves generated by underwaterexplosions or the fall of meteoritesall having far longer wavelengths thanwind waves.

Yet, the largest ever recorded wind waves are commonnot roguewaves inextreme sea states. For example: 29.1 m (95 ft) high waves have beenrecorded on the RRS Discovery in a sea with 18.5 m (61 ft) significant waveheight, so the highest wave is only 1.6 times the significant wave height. Thebiggest recorded by a buoy (as of 2011) was 32.3 m (106 ft) high duringthe 2007 typhoon Krosa near Taiwan.


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Silvinus Clisson Pragash

M.Arch 2nd Sem (landscape architecture)

School of Architecture and Planning
http://en.wikipedia.org/wiki/File:Munk_ICCE_1950_Fig1.svg

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Land and Sea