Download Structure of The Earth - University of Agriculture Abeokuta

ELEMENTS OF
GEOSCIENCES
WMA 210
Dr. G.C. Ufoegbune, Dr O.Z. Ojekunle
Dept of Water Res. Magt. & Agromet
UNAAB. Abeokuta. Ogun State
Nigeria
[email protected]
Definition
• Scope and approaches to Geoscience.
• 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 earth's
system (open systems, closed systems, matter 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'satmosphere and energy system.
• Introduction: Environmental Unity, Steady State,
Residence Time in the Environment.
The 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
The Earth
WMA 210
Structure of the Interior of
Earth
• 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
of 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
of 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
(Calculation of Earth’s 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
Defined
• 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 Earth[1] are at
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
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
Mantle
Core
•
•
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 lessdense 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
Core
• 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
• 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.
Crust
•
•
•
•
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
Common Rocks:
Igneous,
Sedimentary, and
Metamorphic
Part 2
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
to 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
Rocks
• There are three major classes of
rocks, IGNEOUS,
• SEDIMENTARY, and
METAMORPHIC, with the following
attributes:
Igneous 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 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 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
Rock 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 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
TEXTURE 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
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
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
Fundamental
Concepts about
the Earth's
Geology
Part 3
1. The Earth formed about 4.6 billion years
ago, along with the other solar planets and 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/calciumrich 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
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
variable.
3 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 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
Shapes
• 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
Shapes
•
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 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
a 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 Cycle
Part 4
The 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 Cycle
The 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 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 Relief
• Assignment to be submitted in
groups
Denudation 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 subprocesses of cryofracture, insolation weathering, slaking,
salt weathering, bioturbation and anthropogenic impacts.
Factors affecting denudation include:
• Surface topography
• Geology
• Climate (most directly in chemical
weathering)
• Tectonic activity
• Biosphere (fauna and flora)
• Anthropogenic activity
Rates
• 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 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 Floodplains
• A meander occurs when a river alternates
its direction of flow due to the downward
slope of a valley. Because valleys are Vshaped, 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 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 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.
Levees
• 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 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 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 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 water cycle.
Biochemical 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)
• 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)
• 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 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 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 Cycles
Oxygen Cycle
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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 CYCLE
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- 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 CYCLE
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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 CYCLE
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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:[email protected]
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