Environmental Chemistry
Chapter 17:
The Geosphere and Geochemistry
Copyright © 2011 by DBS
Contents
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The Geosphere
Branches of Geochemistry
Physical Form of the Geosphere
The Nature of Solids in the Geosphere
Geochemistry Geosphere-Hydrosphere Interactions and the Formation of
Sediments
Clays
The Geosphere-Atmosphere Interface
The Geosphere-Biosphere Interface
The Geosphere and the Anthrosphere
The Geosphere
The Geosphere
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The geosphere is that part of Earth upon which humans live and from which they
extract most of their food, minerals, and fuel
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Interactions between the geosphere, biosphere, atmosphere, hydrosphere,
anthrosphere are important
Give some examples of
interactions between the
spheres…
The Geosphere
Figure 17.1. Relationship of Geosphere to Other Environmental Spheres
The Geosphere
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Purturbations by mining:
The Geosphere
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Purturbations by mining:
The Geosphere
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Purturbations by mining:
The Geosphere
See also
Lake
Chad,
Africa
The Geosphere
Atmosphere/Geosphere Interaction
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Global Warming: Carbon dioxide causes global warming, drought harmful to
geosphere
– Affects atmosphere by fraction of incoming solar radiation reflected
– Affects hydrosphere by degree of water infiltration to groundwater
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Acidification: Acid rain acidifies soil, releases toxic Al
– Soil is especially important as a medium for plant growth
Anthrosphere/Geosphere Interaction
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Human activities greatly affect the geosphere
– cultivation of crops and the associated washing away of topsoil
– Strip mining
– Waste generation
The Geosphere
Atmosphere/Geosphere Interaction
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Global Warming: Carbon dioxide causes global warming, drought harmful to
geosphere
– Affects atmosphere by fraction of incoming solar radiation reflected
– Affects hydrosphere by degree of water infiltration to groundwater
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Acidification: Acid rain acidifies soil, releases toxic Al
– Soil is especially important as a medium for plant growth
Anthrosphere/Geosphere Interaction
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Human activities greatly affect the geosphere
– cultivation of crops and the associated washing away of topsoil
– Strip mining
– Waste generation
The Geosphere
Geosphere/Hydrsophere Interaction
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Surface alteration affect rainfall infiltration
– Can lead to groundwater depletion
– Which then affects the other spheres.
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Subsurface alteration can affect the anthrosphere
– Hydrofracturing for natural gas production
Geosphere/Biosphere Interaction
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Large areas losing their capacity to retain water and support plant
growth.
– Desertification
Branches of Geochemistry
Branches of Geochemistry
Environmental Geology
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Environmental geology relates geological science to environmental science and
technology
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Complex relationships between the geosphere with the hydrosphere,
atmosphere, biosphere, and anthrosphere
– Pollution from geospheric phenomena, such as volcanic eruptions
– Water contaminants from the geosphere, such as arsenic
– Geospheric pollution from the anthrosphere, hazardous wastes
– Geosphere in an optimum condition to support life
– Most important areas is Biogeochemistry and biogeochemical cycles
Branches of Geochemistry
Engineering Geology
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Engineering geology addresses the ways in which geological materials and
formations are used and dealt with technologically
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• Structures
• Materials science
•Other engineering aspects
– Example: Steepness of slope in siting structures
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Large public works projects such as highways
– Affect geosphere by earth moving, digging, boring
– Detailed knowledge of geosphere upon which they are located
Branches of Geochemistry
Economic Geology and Geospheric Resources
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Economic geology relates geology with the economic resources and natural
capital of the geosphere
– Find and develop essential raw materials, fuel resources
– Economic aspects of locating and constructing structures
– Warn of potential hazards of geosphere
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Extractive materials are non-renewable and removed from the geosphere
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Renewable materials in the form of plant biomass are produced by growing on
the geosphere
Physical Form of the Geosphere
Physical Form of the Geosphere
Measurement of topographic heights and ocean depths:
(i) GPS (satellites) use the oblate (squashed) spheroid model (reference ellipsoid)
(ii) Geoid – an alternative way to reference height – based on Earth’s gravity, can be
approximated by mean sea-level – much more accurate method
Physical Form of the Geosphere
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Earth shaped as a geoid
– The geoid is a representation of the surface of the earth
– Close to spherical, but not a perfect sphere due to gravity variations (e.g.
the density of magma is uneven in the earth’s crust)
According to C.F. Gauss, who first described it, it is the "mathematical figure of
the Earth", a smooth but highly irregular surface that corresponds not to the
actual surface of the Earth's crust, but to a surface which can only be known
through extensive gravitational measurements and calculations.
1. Ocean
2. Reference ellipsoid
3. Local plumb line
4. Continent
5. Geoid
Physical Form of the Geosphere
Theory of plate tectonics, the tectonic cycle
http://www.youtube.com/watch?v=uGcDed4xVD4
Physical Form of the Geosphere
Theory of plate tectonics, the tectonic cycle
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Continents drift atop the flexible athenosphere, Figure 17.2
Physical Form of the Geosphere
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Boundaries between Plates Where Most Geological Processes Occur
– Divergent boundaries where plates move away from each other allowing hot
magma to flow upward and create new lithosphere and ocean ridges
– Convergent boundaries in which plates move toward each other creating a
subduction zone where new magma is formed or mountain ranges created
– Transform fault boundaries in which two plates slide past each other, often
resulting in earthquakes
Physical Form of the Geosphere
Structural Geology
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Geometric forms of geologic structures over a wide size range
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Nature of structures formed by geological processes
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Formation of folds, faults, and other geological structures
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Primary structures resulting from formation of a rock mass from its parent
materials
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Secondary structures from modified, deformed primary structures
– Joints and faults, Figure 17.3
Physical Form of the Geosphere
Internal and Surface Processes
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Internal processes occur below surface level – earthquakes, volcanoes
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Surface processes are confined to the surface – landslides, mudslides,
avalanches, glaciers
The Nature of Solids in the Geosphere
The Nature of Solids in the Geosphere
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Geosphere is layered
– Solid iron-rich inner core
– Molten outer core
– Mantle
– Crust (outer skin accessible by humans,
only 5-40 km thick)
– Lithosphere consists of outer mantle
and crust
The Nature of Solids in the Geosphere
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Mineral is a naturally occurring inorganic solid
– Definite internal crystal structure
– Definite chemical composition
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Rock is a solid, cohesive mass of pure mineral or aggregate of two or more
different minerals
The Nature of Solids in the Geosphere
Structure and Properties of Minerals
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Characterized by two major characteristics
– Chemical formula
– Defined crystal structure, arrangement of atoms and ions
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Physical properties that identify minerals
– Crystal form shown by physical appearance
– Color
– Luster, appearance in reflected light (metallic, vitreous, dull)
– Streak when rubbed across unglazed porcelain
– Hardness ranging from 1 for talc to 10 for diamond
– Fracture, the manner in which minerals break
– Specific gravity
The Nature of Solids in the Geosphere
Kinds of Minerals
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Over 2000 known minerals
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Only about 25 rock-forming minerals
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Crust is 49.5% oxygen, 25.7% silicon, 7.4% aluminum, 4.7% iron, 3.6% calcium,
2.8% sodium, 2.6% potassium, 2.1% magnesium, 1.6% other
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Only about 25 rock-forming minerals compose virtually all Earth’s crust
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Most abundant minerals are silicates
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• Quartz, SiO2
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Secondary minerals formed by alteration of parent minerals
• Orthoclase, KAlSi3O8
– Clays are common secondary minerals
– Clays are silicate minerals, usually containing aluminum
– Olivine, augite, hornblende, and feldspars all form clays
The Nature of Solids in the Geosphere
Table 17.1 Major Mineral Groups in the Earth’s Crust
Mineral group
Common examples
Formula
Silicates
Quartz
SiO2
Olivine
(Mg,Fe)2SiO4
Potassium feldspar
KAlSi3O8
Oxides
Corundum
Al2O3
Magnetite
Fe3O4
Carbonates
Calcite
CaCO3
Dolomite
CaCO3•MgCO3
Sulfides
Sulfates
Halides
Native
elements
Pyrite
Galena
Gypsum
Halite
Fluorite
Copper
Sulfur
FeS2
PbS
CaSO4•2H2O
NaCl
CaF2
Cu
S
The Nature of Solids in the Geosphere
Evaporites
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Soluble salts that precipitate under arid conditions e.g. halite, saltpeter
Igneous, Sedimentary, and Metamorphic Rocks
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Igneous rock from cooling of magma, e.g. granite, basalt, quartz, pyroxene,
olivine, feldspar, magnetite
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Sedimentary rock from exposed and weathered igneous rocks, e.g. sandstone,
conglomerates, shale
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Metamorphic rock from heat and pressure conversion of sedimentary rock
Igneous, Sedimentary, and Metamorphic Rock
Figure 17.4. The Rock Cycle
The Nature of Solids in the Geosphere
Weathering
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Igneous rocks are formed under water-deficient, chemically reducing conditions
of high temperature and high pressure
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Exposed at surface to wet, oxidizing, low temperature, low-pressure conditions
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Under surface conditions rocks disintegrate by a process of weathering
– Forms sediments and soil
– May be physical (freeze/thaw, wet/dry, growth of roots, etc.) or chemical
– Dependent on temperature change
Geochemistry
Geochemistry
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Geochemistry deals with chemical species, reactions and processes in the
geosphere
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Environmental geochemistry is the branch of geochemistry that explores the
complex geochemical interactions involving the geosphere and the other
environmental spheres
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Chemical weathering is an important geochemical phenomenon, slow in dry
conditions, faster in the presence of water
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Water holds the weathering agents in solution and allows for contact with mineral
surfaces,
e.g. CO2, O2, organic acids, sulfur and nitrogen acids, produce H+ in solution
Geochemistry
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Dissolution/precipitation
CaSO4.H2O → Ca2+ + SO42- + 2H2O
Fe2SiO4(s) + 4CO2(g) + 4H2O → 2Fe2+ + 4HCO3- + H4SiO4
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Acid-base reactions
CO2 + H2O → H+ + HCO3-
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Complexation
K2(SiAl2)Al4O20(OH)4(s) + 6C2O42- + 20H+ → 6AlC2O4+(aq) + 6Si(OH)4 + 2K+
(muscovite)
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(complexed Al)
Hydrolysis
CaCO3(s) + H2O + CO2(g) → Ca2+(aq) + 2HCO3-(aq)
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Oxidation-reduction
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4Fe2+ + 8HCO3- + O2(g) 2Fe2O3(s) + 8CO2 + 4H2O
(see 2nd reaction)
Geosphere-Hydrosphere Interactions and
the Formation of Sediments
Geosphere-Hydrosphere Interactions and
the Formation of Sediments
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Water strongly involved with weathering of rock in the geosphere
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Flowing water erodes and shapes the geosphere
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Large quantities of water in underground aquifers in the geosphere
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Precipitation falls on a drainage basin and into a stream
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Streams shape land and mountains creating plains, valleys and sediment
deposits
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Erosion and deposition of matter creates a floodplain
Geosphere-Hydrosphere Interactions and
the Formation of Sediments
Groundwater plays a
crucial role in
geochemical cycling
Figure 17.5. Major
Features of the
Distribution of Water
Underground
Geosphere-Hydrosphere Interactions and
the Formation of Sediments
Figure 17.6. The Water Table and Influences of Surface Features on it
Geosphere-Hydrosphere Interactions and
the Formation of Sediments
Sediments
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Sediments and sedimentary rocks from breakdown and erosion of parent rocks
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Water is the main agent for carrying and forming sediments
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Three ways in which streams carry sedimentary materials:
– Dissolved load from sediment-forming minerals in solution
– Suspended load from solid sedimentary materials carried along in
suspension
– Bed load dragged along the bottom of the stream channel
Geosphere-Hydrosphere Interactions and
the Formation of Sediments
Sediments
Figure 17.7. Sedimentary Materials Carried by a Stream
Geosphere-Hydrosphere Interactions and
the Formation of Sediments
Sediments
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Dissolved load, e.g. Transport of calcium carbonate as dissolved calcium
bicarbonate
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Water containing CO2 (from bacterial action) in contact with CaCO3 rocks will
contain Ca2+ and HCO3- (see reactions above)
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Becomes more basic by loss of CO2 or contact with dissolved base, deposits
insoluble CaCO3
Ca2+ + 2HCO3- → CaCO3(s) + CO2(g) + H2O
Geosphere-Hydrosphere Interactions and
the Formation of Sediments
Phenomena at the Land/Ocean Interface
Berm formed by sedimentation of
material from wave action on
coastal rock
Figure 17.8. Phenomena at the Land/Ocean Interface
Geosphere-Hydrosphere Interactions and
the Formation of Sediments
Effects of Ice
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Enormous ice cover from the Ice Ages had enormous effects on the geosphere
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When glacial ice melts
– Rock carried by the glacier as glacial till
– Rock carried by melting glacial water is outwash
– Piles of rock remaining are moraines
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Effects of non-glacial ice
– Freezing and expansion of water in pores and small rock crevices cause
physical weathering
– Freeze/thaw cycles can be destructive to structures (stone buildings)
Clays
Clays
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Clays are a group of microcrystalline secondary minerals consisting of
aluminosilicates with sheet like structures and include the following
main types
Montmorillonite, Al2(OH)2Si4O10
Illite , K0-2Al4(Si6-8Al0-2)O20(OH)4
Kaolinite, Al2Si2O5(OH)4
Clays
• Formation of kaolinite from potassium feldspar rock (KAlSi3O8)
2KAlSi3O8(s) + 2H+ + 9H2O  Al2Si2O5(OH)4(s) + 2K+(aq) + 4H4SiO4(aq)
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Clays contain sodium, potassium, magnesium, calcium, iron, trace quantities of
other metals
Clays
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Clay Minerals
– Aluminosilicates (produced by weathering rocks)
– Sheet silicates formed from tetrahedral silica and octahedral alumina
Silicon
tetrahedron
Aluminium
Octahedron
Clays
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Clay Minerals
– Different combinations of tetrahedral and octahedral sheets form different clay minerals
– Large space for water or cations to collect
(a) A 1:1 clay mineral (e.g., kaolinite), and 2:1 clay minerals (b) illite and (c)
montmorillonite
Clay minerals
photographed
with an electron
Microscope.
Note: they are plate
or flake like and
are stacked on top
of each other.
Clays
Figure 17.9. Representation of the Structure of Kaolinite, a Two-Layer Clay
Clays
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Clays are negatively charged, bind and exchange H+, Mg2+, K+, Na+, NH4+
– Bind and exchange these cations, available as plant nutrients
– Cation exchange capacity, CEC
– Clays suspended as colloidal particles in water
– Leached from soil and carried to lower soil layers
The Geosphere-Atmosphere Interface
The Geosphere-Atmosphere Interface
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Geosphere eroded and abraded by wind
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Water carried from the atmosphere causes weathering and erosion
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Moist, oxidizing atmosphere conducive to oxidative weathering
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Atmosphere strongly influenced by the geosphere
– Dark rock, soil absorb sunlight and radiate heat
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Sulfur dioxide and hydrogen sulfide emitted to the atmosphere
– Greenhouse gas methane from the geosphere to atmosphere
– Dust from the geosphere gets into atmosphere
The Geosphere-Biosphere Interface
The Geosphere-Biosphere Interface
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Most plants exist on soil
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Other life forms such as earthworms, fungi, and bacteria exist on or in soil
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Minerals, such as limestone, were produced by biological action
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Fossil fuels were produced biologically
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The geosphere is a source of elements essential to life
– Iodine to prevent goiter
– Fluoride for teeth
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Iron
– Zinc
– Selenium
The Geosphere and the Anthrosphere
The Geosphere and the Anthrosphere
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Most of the anthrosphere is located on or buried within the geosphere
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Nature and stability of structures strongly dependent on the geosphere
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Ease and type of mining of minerals depends on the nature of the geosphere
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Sustainable extraction of materials from the geosphere is a major sustainability
challenge
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Anthrospheric activities may strongly affect or damage the geosphere
– Pollution and loss of topsoil
– Saltwater pollution makes soil unproductive
– Sulfur dioxide and metal pollution from metals smelting may damage soil
– Strip-mining and mountain top removal mining of coal can scar the
geosphere
– Underground mining of coal followed by coal mine fires have been very
detrimental to the geosphere