ELEMENTS OF ELEMENTS OF GEOSCIENCESGEOSCIENCES

WMA 210WMA 210Dr. G.C. Ufoegbune, Dr O.Z. OjekunleDr. G.C. Ufoegbune, Dr O.Z. Ojekunle

Dept of Water Res. Magt. & AgrometDept of Water Res. Magt. & AgrometUNAAB. Abeokuta. Ogun StateUNAAB. Abeokuta. Ogun State

NigeriaNigeriaoojekunle@yahoo.com

DefinitionDefinition

• Scope and approaches to Geo-science.

• Geo-science as Earth science or sciences related to the planet Earth.

• Earth science includes the study of atmosphere, hydrosphere, oceans and biosphere as well as the solid earth.

The nature, composition and classification of the The nature, composition and classification of the earth's system (open systems, closed systems, matter earth's system (open systems, closed systems, matter

and energy classification of rocks).and energy classification of rocks).

• Examination of system as related to the Universe. Definition of Universe. The Earth as a system.

• Open and Closed systems: Definition • The Earth as open and closed systems in relation to mather

and energy.• Mather and energy as the building blocks of physical and

biological environment • Sources of energy in the environment.• Characteristics of systems:• Systems feedback – Negative and Positive feedback• Negative and positive feedback on Earth. Implications:

Ozone depletion, Urban degradation, pollution in water bodies, etc.

Environmental processes; the atmosphere, earth's-Environmental processes; the atmosphere, earth's-atmosphere and energy systematmosphere and energy system. .

• Introduction: Environmental Unity, Steady State, Residence Time in the Environment.

The Inter-relationshipThe Inter-relationship• The inter-relationship between the atmosphere,

hydrosphere, lithosphere, biosphere and man. Lithologic and hydrologic cycle, denudation processes, action of flowing water and erosion, flood plain features and characteristics of wetlands; deltas, classification of types of relief, biogeochemical cycle; man's interaction with natural environment and energy systems.

• Composition of the Earth's crust; minerals and rocks (classifications of rocks); Lithologic cycle; classification of types of relief; denudation processes; action of flowing water and erosion; flood-plain features, deltas; biogeochemical cycle.

•  

Structure of Structure of The EarthThe Earth

WMA 210WMA 210

Structure of the Interior of Structure of the Interior of EarthEarth

• Earth has a diameter of about 12,756 km (7,972 mi). The Earth's interior consists of rock and metal. It is made up of four main layers:

• 1) the inner core: a solid metal core made up of nickel and iron (2440 km diameter)

• 2) the outer core: a liquid molten core of nickel and iron

• 3) the mantle: dense and mostly solid silicate rock

• 4) the crust: thin silicate rock material

This diagram shows the different layers found inside the Earth.

Structure of the Interior Structure of the Interior of Earthof Earth

• The temperature in the core is hotter than the Sun's surface. This intense heat from the inner core causes material in the outer core and mantle to move around.

• The movement of material deep within the Earth may cause large plates made of the crust and upper mantle to move slowly over the Earth’s surface. It is also possible that the movements generate the Earth's magnetic field, called the magnetosphere.

Structure of the Interior Structure of the Interior of Earthof Earth

• The interior structure of the Earth, similar to the outer, is layered. These layers can be defined by either their chemical or their rheological properties. The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. Scientific understanding of Earth's internal structure is based on observations of topography and bathymetry , observations of rock in outcrop, samples brought to the surface from greater depths by volcanic activity, analysis of the seismic waves that pass through the Earth, measurements of the gravity field of the Earth, and experiments with crystalline solids at pressures and temperatures characteristic of the Earth's deep interior.

Assumptions Assumptions (Calculation of Earth’s (Calculation of Earth’s Mass)Mass)

• The force exerted by Earth's gravity can be used to calculate its mass, and by estimating the volume of the planet, its average density can be calculated. Astronomers can also calculate Earth's mass from its orbit and effects on nearby planetary bodies. Observations of rocks, bodies of water and atmosphere allow estimation of the mass, volume and density of rocks to a certain depth, so the remaining mass must be in the deeper layers.

Structure of the Earth Structure of the Earth DefinedDefined

• The structure of Earth can be defined in two ways:

• by mechanical properties such as rheology, or chemically.

• Mechanically, it can be divided into lithosphere, asthenosphere, mesosphere, outer core, and the inner core.

• The interior of the earth is divided into 5 important layers.

• Chemically, Earth can be divided into the crust, upper mantle, lower mantle, outer core, and inner core.

The geologic component layers of EarthThe geologic component layers of Earth[1] are at are at

the following depths below the surface:the following depths below the surface: Depth Layer

Kilometers Miles

0–60 0–37 Lithosphere (locally varies between 5 and 200 km)

0–35 0–22 … Crust (locally varies between 5 and 70 km)

35–60 22–37 … Uppermost part of mantle

7 35–2,890 22–1,790 Mantle

100–200 62–125 … Asthenosphere

35–660 6 22–410 … Upper mantle

660–2,890 410–1,790 … Lower mantle

2,890–5,150 1,790–3,160 Outer core

5,150–6,360 3,160–3,954 Inner core

CoreCore

• The average density of Earth is 5,515 kg/m3. Since the average density of surface material is only around 3,000 kg/m3, we must conclude that denser materials exist within Earth's core. Further evidence for the high density core comes from the study of seismology.

• Seismic measurements show that the core is divided into two parts, a solid inner core with a radius of ~1,220 km and a liquid outer core extending beyond it to a radius of ~3,400 km. The solid inner core was discovered in 1936 by Inge Lehmann and is generally believed to be composed primarily of iron and some nickel. In early stages of Earth's formation about 4.5 billion (4.5×109) years ago, melting would have caused denser substances to sink toward the center in a process called planetary differentiation (see also the iron catastrophe), while less-dense materials would have migrated to the crust. The core is thus believed to largely be composed of iron (80%), along with nickel and one or more light elements, whereas other dense elements, such as lead and uranium, either are too rare to be significant or tend to bind to lighter elements and thus remain in the crust (see felsic materials). Some have argued that the inner core may be in the form of a single iron crystal.[2]

The Centre is occupied by the Core, which is about 3500km (2200mi) in radius and it is very hot of about 3000-5000 oC

CoreCore• Dynamo theory suggests that convection in the outer core,

combined with the Coriolis effect, gives rise to Earth's magnetic field. The solid inner core is too hot to hold a permanent magnetic field (see Curie temperature) but probably acts to stabilize the magnetic field generated by the liquid outer core. The average magnetic field strength in the Earth's outer core was measured to be 25 Gauss, 50 times stronger than the magnetic field at the surface.

• The current scientific explanation for the Earth's temperature gradient is a combination of heat left over from the planet's initial formation, decay of radioactive elements, and freezing of the inner core

Mantle Mantle • Schematic 'hi' of the

interior of Earth. 1. continental crust - 2. oceanic crust - 3. upper mantle - 4. lower mantle - 5. outer core - 6. inner core - A: Mohorovičić discontinuity - B: Gutenberg Discontinuity - C: Lehmann discontinuity

Enclosing the metallic core is the mantle, a rock shell about 2900 km (1800 mi) thick

Earth's mantle• Earth's mantle extends to a depth of 2,890 km, making it the

thickest layer of the Earth. The pressure, at the bottom of the mantle, is ~140 GPa (1.4 Matm). The mantle is composed of silicate rocks that are rich in iron and magnesium relative to the overlying crust. Although solid, the high temperatures within the mantle cause the silicate material to be sufficiently ductile that it can flow on very long timescales. 13 Convection of the mantle is expressed at the surface through the motions of tectonic plates. The melting point and viscosity of a substance depends on the pressure it is under. As there is intense and increasing pressure as one travels deeper into the mantle, the lower part of the mantle flows less easily than does the upper mantle (chemical changes within the mantle may also be important). The viscosity of the mantle ranges between 1021 and 1024 Pa·s, depending on depth.[12] In comparison, the viscosity of water is approximately 10−3 Pa·s and that of pitch is 107 Pa·s.

CrustCrust

• The crust ranges from 5–70 km in depth and is the outermost layer. The thin parts are the oceanic crust, which underlie the ocean basins (5–10 km) and are composed of dense (mafic) iron magnesium silicate rocks, like basalt.

• The thicker crust is continental crust, which is less dense and composed of (felsic) sodium potassium aluminium silicate rocks, like granite. The rocks of the crust fall into two major categories - sial and sima (Suess,1831–1914).

• As the main mineral constituents of the continental mass are silica and alumina, it is thus called sial (si-silica, 65–75% and al-alumina). The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium). It is estimated that sima starts about 11 km below the Conrad discontinuity, a second order discontinuity. The uppermost mantle together with the crust constitutes the lithosphere. The crust-mantle boundary occurs as two physically different events. First, there is a discontinuity in the seismic velocity, which is known as the Mohorovičić discontinuity or Moho.

• Many rocks now making up Earth's crust formed less than 100 million (1×108) years ago; however the oldest known mineral grains are 4.4 billion (4.4×109) years old, indicating that Earth has had a solid crust for at least that long.

Classification of Classification of Common Rocks:Common Rocks:

Igneous, Igneous, Sedimentary, and Sedimentary, and MetamorphicMetamorphic

Part 2Part 2

What is a Rock?What is a Rock?• A rock is a naturally occurring aggregate of

minerals, and certain non-mineral materials such as fossils and glass.  Just as minerals are the building blocks of rocks, rocks in turn are the natural building blocks of the Earth's LITHOSPHERE (crust and mantle down to a depth of about 100 km), ASTHENOSPHERE (although this layer, in the depth range from about 100 to 250 km, is partially molten), MESOSPHERE (mantle in the depth range from about 250 to 2900 km), and even part of the CORE (while the outer core is molten, the inner core is solid). 

Forms Rocks are Exposed Forms Rocks are Exposed to the Surfaceto the Surface

• Most rocks now exposed at the surface of the Earth formed in or on continental or oceanic crust.  Many such rocks, formed beneath the surface and now exposed at the surface, were delivered to the surface from great depths in the crust and in rare cases from the underlying mantle.  There are two general ways that rocks come to be exposed at the surface:

• Formation at the surface (e.g., crystallization of lava, precipitation of calcite or dolomite from sea water)

• Formation below the surface, followed by tectonic uplift and removal of the overlying material by erosion

Three Major Classes of Three Major Classes of RocksRocks

• There are three major classes of rocks, IGNEOUS,

• SEDIMENTARY, and METAMORPHIC, with the following attributes:

Igneous RockIgneous Rock• IGNEOUS ROCKS form by crystallization

from molten or partially material, called 4 MAGMA.  Magma comes mainly from two places where it is formed, (1) in the asthenosphere and (2) in the base of the crust above subducting lithosphere at a convergent plate boundary. 

• There are two subclasses of igneous rock, • VOLCANIC (sometime called EXTRUSIVE), and • PLUTONIC (sometimes called INTRUSIVE).

Volcanic and Plutonic RocksVolcanic and Plutonic Rocks• VOLCANIC ROCKS form at the Earth's surface. 

They cool and crystallized from magma which has spilled out onto the surface at a volcano.  At the surface, the magma is more familiarly known as LAVA.

• PLUTONIC ROCKS form from magma that cools and crystallizes beneath the Earth's surface.  In a sense, this is the portion of the magma that never makes it to the surface.  For the plutonic rock to become exposed at the surface, it must be tectonically uplifted and the overlying material must be removed by erosion.

Sedimentary RockSedimentary Rock• SEDIMENTARY ROCKS form from material that

has accumulated on the Earth's surface.  The general term for the process of accumulation is DEPOSITION.  The material consists of the products of weathering and erosion, and other materials available at the surface of the Earth, such as organic material.  The process by which this otherwise unconsolidated material becomes solidified into rock is variously referred to LITHIFICATION (literally turned into rock), DIAGENESIS or CEMENTATION. 

Similarity between Volcanic Similarity between Volcanic Rock and Sedimentary RockRock and Sedimentary Rock• Like volcanic rocks, some sedimentary

rocks are "lithified" right at the surface, for instance by direct precipitation from sea water.  Other sedimentary rocks, like plutonic igneous rocks, are "lithified" below the surface, when they are buried under the weight of overlying sediment.  And like the plutonic rocks, sedimentary rocks which were lithified below the surface only become exposed at the surface by tectonic uplift and erosion of the overlying material.

Metamorphic RockMetamorphic Rock• METAMORPHIC ROCKS form when a sedimentary or

igneous rock is exposed to high pressure, high temperature, or both, deep below the surface of the Earth.  The process, METAMORPHISM, produces fundamental changes in the mineralogy and texture of the rock.  The original rock, prior to metamorphism, is referred to as the PROTOLITH.  The protolith can be either an igneous rock or a sedimentary rock, as just indicated.  The protolith could also be a previously metamorphosed rock.  Ultimately however, if you go far enough back into the history of a metamorphic rock you would find that the first protolith was either a sedimentary or igneous rock.  Because all metamorphic rocks form below the surface, for them to become exposed at the surface, they must undergo tectonic uplift and removal of the overlying material by erosion.  

CLASSIFICATION OF ROCK BY CLASSIFICATION OF ROCK BY TEXTURE AND COMPOSITIONTEXTURE AND COMPOSITION

• The classification of rocks is based on two criteria, TEXTURE and COMPOSITION.  The texture has to do with the sizes and shapes of mineral grains and other constituents in a rock, and how these sizes and shapes relate to each other.  Such factors are controlled by the process which formed the rock.  Because igneous, sedimentary, and metamorphic processes are distinct, so too the resulting textures are distinct. 

CLASSIFICATION OF ROCK BY TEXTURE AND CLASSIFICATION OF ROCK BY TEXTURE AND COMPOSITION (cont)COMPOSITION (cont)

• Thus there are distinct igneous textures, distinct sedimentary texture, and distinct metamorphic textures.  For the purposes of this exercise and routine classification, the kinds of minerals and their proportions, or MINERALOGY, are taken as the natural expression of composition.  Fortunately for you, just as the three classes of rocks each have distinct textures, so too do they have distinct mineralogies.  Details of TEXTURE and COMPOSITION are discussed in the individual sections on igneous, sedimentary and metamorphic rocks

CLASSIFICATION OF ROCK BY TEXTURE AND CLASSIFICATION OF ROCK BY TEXTURE AND COMPOSITION (cont)COMPOSITION (cont)

• Just a note here with regard to grains size.  The terms APHANITIC and PHANERITIC mean fine-grained and coarse-grained respectively.  Generally, aphanitic means that the grains are too small to see or identify, while phaneritic means that the grains are big enough to see and identify, but the terms are used differently in each the classes of rocks.  In igneous rocks the division between aphanitic and phaneritic is taken to be at a grain size of 1/16 mm.  If the grain size is larger than 1/16 mm, the texture is said to be phaneritic.  If the grain size is less than 1/16 mm, the texture is said to be aphanitic.  In sedimentary rocks, the formal division between aphanitic and phaneritic is taken to be 1/256 mm.  For metamorphic rocks the distinction between aphanitic and phaneritic is less quantifiable, but the general meanings are the same.

The Six The Six Fundamental Fundamental

Concepts about Concepts about the Earth's the Earth's

GeologyGeologyPart 3Part 3

1. The Earth formed about 4.6 billion years 1. The Earth formed about 4.6 billion years ago, along with the other solar planets and ago, along with the other solar planets and

the Sun itself.the Sun itself.

• The planets built up by accretion of rocky and gaseous debris (asteroidal, planetesimal [meteoritic] materials and comets) through collision of orbiting bodies. Aided by gravitational attraction, early on the assembling Earth underwent partial to complete melting, separation of different materials into an inner and outer core (iron-nickel), and extensive interior mantle, (iron/magnesium/calcium-rich silicates), and a thin crust (enriched in silica, sodium/potassium/aluminum), all (except the outer core) solidifying by cooling over the first few hundred million years; escaping gases produced an atmosphere (H, CO2, N, CH4) were held above the solid Earth by gravity owing to its large mass; in time (about 4 billion years ago), the Earth's exterior cooled sufficiently to allow vast volumes of water vapor to condense, forming in lower areas great concentrations of water collection into oceanic basins

2 The Earth's materials are diverse and 2 The Earth's materials are diverse and variable.variable.

• Most variation occurs in the outermost 200 kilometers, in the lithosphere. Igneous rocks form directly by crystallizationof hot melts made up of silicates (SimOn) combined with Fe, Mg, Ca, Al, Na, K, Ti, H2O). Minerals formed from these make up nearly all the mantle and crust. Rocks at the surface decompose/disintegrate by reaction with the atmosphere/hydrosphere to produce solid debris and soluble chemicals that are transported/deposited to form sediments, that upon burial are converted to Sedimentary rocks. Previously formed rocks that are heated and pressurized when buried to shallow to moderate depths (5 to 70 km) of the crust recrystallize as solids to form Metamorphic rocks (some may melt). The above processes comprise the Rock Cycle, shown below, and discussed in more detail below.

2 The Earth's materials are diverse and 2 The Earth's materials are diverse and variable.variable.

3 It Have Different Segmented Layer of3 It Have Different Segmented Layer of

• The Earth's outer shells (crust and upper mantle = lithosphere) about150-200 kilometers thick under the continents (less so under the oceans) are subjected to dynamic forces that cause segments of the shells and materials at the top, to break up into plates and deposits on them that move laterally, bringing about deformation of their constituent rocks (mainly in and on the crust) by bending, folding, flowing, fracturing, and movement of blocks along faults. The dybamic processes, driven mainly by heat and gravity and resultant convection within and below the lithosphere (in the mantle), move plate units either away from each other or against each other (both situations can affect a plate); this general motion is called plate tectonics. Plates diverge from ridges within oceanic basics (lower areas underlain by basaltic crust) and converge against boundaries of other plates (whose outer rocks are either oceanic or continental in nature and composition), causing melting, volcanism, metamorphism, mountain building, rise/fall of crustal blocks, continental growth and splitting.

It principle folds areIt principle folds are• The principal types of folds

and faults are shown in the two diagrams below; the extensional fault is commonly known as a normal fault, the compressional type is called a reverse fault if high angle and a thrust fault if low angle, the transform fault is one type of wrench or rift faults that is associated with oceanic ridges.

4 Distortion causes Weathering and forming 4 Distortion causes Weathering and forming ShapesShapes

• The distortions (lateral and/or with up-down movements) of crustal materials combine with physical and chemical reactions between atmospheric constituents (mainly oxygen and water) that weather (breakdown and/or dissolve) rocks which are then eroded, transported (by running water, ice, wind, gravity) and deposited in low surficial locations on land or in water bodies (oceans). These actions contiually modify the shape of the land and ocean surfaces producing a wide range of continental and oceanic landforms (mountains, valleys, plateaus, plains, volcanic edifices, etc.), developing a wide variety of landscapes.(

4 Distortion causes Weathering and forming 4 Distortion causes Weathering and forming ShapesShapes

• Landforms development is often a complex process requiring long time periods during which specific landform types take shape, evolve, and disappear. Factors involved, besides time, are the actions of shaping forces such as running water, etc., the type(s) of climate a region experiences (can change from humid to arid or reverse), the nature and resistance to erosion of the various rock type present and their structural configuration, the history of deformation over time, and rises and falls of the regional elevations (through isostasy - a tendency for the crust to assume altitudes that maintain balance [equilibrium] within the Earth's gravitational field).

5. The Earth Is Dynamic5. The Earth Is Dynamic

• Since its beginning, the Earth has been an active, dynamic planet that experiences continual changes in its interior and especially its ouer lithosphere and surface. Its continents have grown relative to oceanic crust and have shifted in position on a standard global surface (continental drift). Most of Earth's history (expressed sequentially as the Geologic Time Scale) is best deciphered in its rocks, particularly sedimentary ones,that record sequences of modifying events (deduced in part through patterns of lifeforms [usually as fossils] changes (by evolutionary processes) and from rock age measurements (based on fixed rate radioactive decay).

6. The Earth surficial environments operate as 6. The Earth surficial environments operate as a complex, interrelated system of unitsa complex, interrelated system of units

• The Earth surficial environments operate as a complex, interrelated system of units and features best categorized in terms of the physical/chemical components of the Geosphere. Atmosphere, Hydrosphere, and Biosphere powered by solar and internal heat that interact at, just below, and above the global surface to produce a series of conditions that aid, inhibit, and otherwise affect Humans and all living creatures. The study of how these "Spheres" interact, exchange energy, and produce positive and/or negative feedback is called Earth Systems Science. This version of the definitive Bretherton diagram suggests some of these inputs and effects.

The Rock CycleThe Rock CyclePart 4Part 4

The Rock CycleThe Rock Cycle

• To discuss this subject, we will use these two diagrams; the first shows what is known as the Rock Cycle (possible changes from one rock type or mode of origin into others) and the second indicates the names of the major rock types in each of the three main groups: Igneous; Sedimentary; Metamorphic:

The Rock CycleThe Rock Cycle

The General Pattern of Rock FormationThe General Pattern of Rock Formation

• The general pattern followed in the RC is shown in the first of the two diagrams at the beginning of this subsection. It can be summarized verbally in this sequence: Molten rock ---> Igneous Rock ---> W/E of igneous rock ---> Sediments ---> Sedimentary Rock ---> Sedimentary and Igneous Rocks, on burial, experience heat and pressure ---> Metamorphic Rock ---> further heating/pressure ---> Molten Rock. The process can then repeat. One added feature: any igneous, sedimentary, or metamorphic rock at/near the surface can undergo W/E --- Sediment. The energy driving the RC comes from three principal sources:

• 1) Solar - the Sun's radiation provides kinetic energy to move air and water/ice;

• 2) Gravitational - rock and water movements downslope;

• 3) Thermal - trapped heat emanating mainly from the Earth's interior.

Types of WeatheringTypes of Weathering

• Atmospheric weathering (H2O, O2, and CO2 and near surface weathering mainly by water affect all rocks. Physical weathering: roots, still and moving water, wind, human activities fractures, grinds, and flakes rocks into particles. Chemical weathering produces acid conditions that dissolves rock (example: sinkholes in limestone).

What Is ReliefWhat Is Relief• Assignment to be submitted in

groups

Denudation and its ProcesssDenudation and its Processs

• In geology, denudation is the long-term sum of processes that cause the wearing away of the earth’s surface leading to a reduction in elevation and relief of landforms and landscapes. Endogenetic processes such as volcanoes, earthquakes, and plate tectonics uplift and expose continental crust to the exogenetic denudation

• Processes• Denudation incorporates mechanical, biological and

chemical processes of erosion, weathering and mass wasting. Denudation can involve the removal of both solid particles and dissolved material. These include sub-processes of cryofracture, insolation weathering, slaking, salt weathering, bioturbation and anthropogenic impacts.

Factors affecting denudation include:Factors affecting denudation include:

• Surface topography• Geology• Climate (most directly in

chemical weathering)• Tectonic activity• Biosphere (fauna and flora)• Anthropogenic activity

RatesRates

• Modern denudation estimates are usually based on stream load measurements taken at gauging stations. Suspended load, bed load, and dissolved load are included in measurements. The weight of the load is converted to volumetric units and the load volume is divided by the area of the watershed above the gauging station. The result is an estimate of the wearing down of the Earth's surface in inches or centimeters per 1000 years. In most cases no adjustments are made for human impact, which causes the measurements to be inflated.

Features of a Flood PlainFeatures of a Flood Plain

• A flood plain is a type of geological feature that results when a river periodically overflows its banks due to rainfall, snow melt or other factors. Floodplains are initially formed due to the meandering course of a river gradually.

• Floodplains were critical to the survival of human civilization in antiquity because of their role in promoting agriculture, such as the annual flooding of the Nile River delta in Egypt.

• Flood plains contain other geological features such as oxbow lakes, point bars and natural levees due to the erosion and deposition of alluvium, or sediment.

Meanders and FloodplainsMeanders and Floodplains

• A meander occurs when a river alternates its direction of flow due to the downward slope of a valley. Because valleys are V-shaped, this creates an alternating course for the river as it flows toward the ocean or sea. As the meander approaches the ocean, the valley flattens out and the course of the river widens. When the water overflows, it carries layers of sediment and gravel that create a floodplain.

Oxbow LakesOxbow Lakes

• An oxbow lake is a crescent-shaped lake that results from the meandering course of a river along a floodplain.

• According to Enchanted Gardens Wetlands Restoration, the defining factor in the formation of an oxbow lake is erosion.

• Water flows more quickly on the inside edge of a bend than it does on the outside edge, eroding the two adjacent banks on either end of the meander over time and diverting the water flow along a straighter path. The cut-off portion of the river becomes an oxbow lake.

• Oxbow lakes eventually become wetland due to the deposit of sediment and lack of water flow.

Point BarsPoint Bars

• Point bars consist of alluvium that has been swept or rolled into place by secondary water flow at the bottom of the river. According to MIT, secondary water flow results from a pressure differential created by differing velocities of primary water flow along a curved path. The pressure causes gravel and silt to roll or be swept into place, creating a gentle slope that matches the riverbank's elevation.

LeveesLevees

• Natural levees form when a river periodically floods its bank and deposits coarse alluvium such as gravel onto the banks in progressively higher stages when the river spreads and slows down its flow. If the river is not flooding, alluvial deposits can settle on the riverbed, thus raising the river level. Natural levees act as raised boundaries against rising water levels.

River deltaRiver delta

• A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river. Over long periods of time, this deposition builds the characteristic geographic pattern of a river delta.

• The Greek historian Herodotus coined the term delta for the Nile River delta because the sediment deposited at its mouth had the shape of the upper-case Greek letter Delta: Δ.

Types of DeltasTypes of Deltas

• River deltas form when a river carrying sediment reaches a body of standing water, such as a lake, ocean, or reservoir.

• Wave-dominated deltas• Tide-dominated deltas• Gilbert deltas• Estuaries• Inland deltas• Deltas on Mars• Researchers have found a number of examples of

deltas that formed in Martian lakes. Finding deltas is a major sign that Mars once had a lot of water. Deltas have been found over a wide geographical range. Below are pictures of a few.

Biogeochemical cycleBiogeochemical cycle• In ecology and Earth science, a biogeochemical cycle or

nutrient cycle is a pathway by which a chemical element or molecule moves through both biotic (biosphere) and abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth.

• In effect, the element is recycled, although in some cycles there may be places (called reservoirs) where the element is accumulated or held for a long period of time (such as an ocean or lake for water).

• Water, for example, is always recycled through the water cycle, as shown in the diagram. The water undergoes evaporation, condensation, and precipitation, falling back to Earth clean and fresh.

• Elements, chemical compounds, and other forms of matter are passed from one organism to another and from one part of the biosphere to another through the biogeochemical cycles.

A commonly cited example is the A commonly cited example is the water cycle..

Biochemical CyclesBiochemical Cycles• All chemical elements occurring in organisms are

part of biogeochemical cycles. In addition to being a part of living organisms, these chemical elements also cycle through abiotic factors of ecosystems such as water (hydrosphere), land (lithosphere), and the air (atmosphere). The living factors of the planet can be referred to collectively as the biosphere. All the nutrients—such as carbon, nitrogen, oxygen, phosphorus, and sulfur—used in ecosystems by living organisms operate on a closed system; therefore, these chemicals are recycled instead of being lost and replenished constantly such as in an open system.

Biochemical Cycles (Cont)Biochemical Cycles (Cont)• The flow of energy in an ecosystem is an open

system; the sun constantly gives the planet energy in the form of light while it is eventually used and lost in the form of heat throughout the trophic levels of a food web. Carbon is used to make carbohydrates, fats, and proteins, the major sources of food energy. These compounds are oxidized to release carbon dioxide, which can be captured by plants to make organic compounds. The chemical reaction is powered by the light energy of the sun.

Biochemical Cycles (Cont)Biochemical Cycles (Cont)• It is possible for an ecosystem to obtain energy

without sunlight. Carbon must be combined with hydrogen and oxygen in order to be utilized as an energy source, and this process depends on sunlight. Ecosystems in the deep sea, where no sunlight can penetrate, use sulfur. Hydrogen sulfide near hydrothermal vents can be utilized by organisms such as the giant tube worm. In the sulfur cycle, sulfur can be forever recycled as a source of energy. Energy can be released through the oxidation and reduction of sulfur compounds (e.g., oxidizing elemental sulfur to sulfite and then to sulfate).

Important CyclesImportant Cycles

• The most well-known and important biogeochemical cycles, for example, include the carbon cycle, the nitrogen cycle, the oxygen cycle, the phosphorus cycle, the sulfur cycle and the water cycle. There are many biogeochemical cycles that are currently being studied for the first time as climate change and human impacts are drastically changing the speed, intensity, and balance of these relatively unknown cycles. These newly studied biogeochemical cycles include the mercury cycle and the human-caused cycle of atrazine, which may affect certain species.

• Biogeochemical cycles always involve hot equilibrium states: a balance in the cycling of the element between compartments. However, overall balance may involve compartments distributed on a global scale.

The Nitrogen CycleThe Nitrogen Cycle• Nitrogen comprises 78.08 % of the

atmosphere making it the largest constituent of the gaseous envelope that surrounds the Earth. Nitrogen is important in the make up of organic molecules like proteins. Unfortunately, nitrogen is inaccessible to most living organisms. Nitrogen must be “fixed” by soil bacteria living in association with the roots of particular plant like legumes, clover, alfalfa, soybeans, peas, peanuts, and beans. Living on nodules around the roots of legumes, the bacteria chemically combine nitrogen in the air to form nitrates (NO3) and ammonia (NH3) making it available to plants. Organisms that feed on the plants ingest the nitrogen and release it in organic wastes. Denitrifying bacteria frees the nitrogen from the wastes returning it to the atmosphere.

Nitrogen CyclesNitrogen Cycles

Oxygen CycleOxygen Cycle

• Oxygen is the second most abundant gas in Earth’s atmosphere and an essential element of most organic molecules. Though oxygen is passed between the lithosphere, biosphere and atmosphere in a variety of ways,

• photosynthesizing vegetation is largely responsible for oxygen found in the atmosphere.

• The cycling of oxygen through the Earth system is also accomplished by weathering of carbonate rock.

• Some atmospheric oxygen is bound to water molecules from plant transpiration and evaporation.

• Oxygen is also bound to carbon dioxide and released into the atmosphere during animal respiration.

CARBON CYCLECARBON CYCLE •   - Carbon (C) enters

the biosphere during photosynthesis: CO2 + H2O ---> C6H12O6 + O2 + H2O     - Carbon is returned to the biosphere in cellular respiration:  O2 +H2O + C6H12O6 ---> CO2 +H2O + energy

PHOSPHORUS CYCLEPHOSPHORUS CYCLE   • Facts: •       - Component of DNA, RNA,

ATP, proteins and enzymes         - Cycles in a sedimentary cylce         - A good example of how a mineral element becomes part of an organism.         - The source of Phosphorus (P) is rock.         - It is released into the cylce through erosion or mining.         - It is soluble in H2O as phosphate (PO4)         - It is taken up by plant roots, then travels through food chains.         - It is returned to sediment

SULFUR CYCLESULFUR CYCLE         • Facts: •               - Component of protein

              - Cycles in both a gas and sedimentary cycle.                - The source of Sulfur is the lithosphere(earth's crust.                - Sulfur (S) enters the atmosphere as hydrogen sulfide (H2S) during fossil fuel combustion, volcanic eruprtions, gas exchange at ocean surfaces, and decomposition.                 - H2S is immediately oxidized to sulfur dioxide (SO2)                 - SO2 and water vapor makes H2SO4 ( a weak sulfuric acid),which is then carried to Earth in rainfall.                 - Sulfur in soluble form is taken up by plant roots and incorporated into amino acids such as cysteine. It then travels through the food chain and is eventually released                   through decomposition.

• Dr. Z.O. Ojekunle

• University of Agriculture

• College of Environmental Resources Management

• Department of Water Resources Management and Agrometeorology.

• Email:oojekunle@yahoo.com

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