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Glossary
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Abyssal Plain
Smooth, almost level area of the deep ocean floor in which the gradient
is likely to be as low as 1:10,000. Allaby and Allaby (1990)
Acid
A substance which, on being dissolved in water produces hydrogen ions
at concentrations which exceed those found in pure water. Acids are strongly
corrosive and will dissolve metals from many natural materials, e.g. rock.
Acid Hydrolysis
The mechanism by which silicate rock minerals react with, and are broken
down by, the hydrogen ions produced when acids dissolve in water.
Acid rain
Rain which has become more acidic from falling through acidic pollutant
gases, principally sulfur dioxide and nitrogen oxides, which dissolve
into water in the atmosphere.
Aggregates
General term used to describe natural (sometimes artificial) rock which
has been crushed or naturally weathered to a size suitable for use in
concrete. It is the third ingredient (together with water and cement)
used in the production of concrete.
Alkali elements (metals)
The group I elements lithium, sodium, potassium, rubidium, caesium and
francium. All are very electropositive and form ions with a positive charge
of +1. Sharp (1990)
Alkaline earth elements (metals)
The group II elements magnesium, calcium, strontium, barium and radium
which are very electropositive and form ions with a charge of 2+. Sharp
(1990)
Alluvial
Applied to the environments, action and products of rivers or streams.
Allaby and Allaby (1990)
Alumino-silicate
Silicate containing aluminium. Important types are feldspar, mica, zeolites
and some clay minerals. (See: Silicate and Clay minerals). Sharp (1990)
Anion
The negatively charged ion from an ionic bonded compound (e.g. F-).
Aquatic ecosystem
Any ecosystem of which the principal component is water, such as ponds,
lakes, rivers, streams and oceans. Lawrence (1995)
Aquatic life
See Aquatic ecosystem.
Atmosphere
The gaseous envelope surrounding planets. The term is generally applied
to the whole body of terrestrial air. The earth's atmosphere is composed
mainly of nitrogen, oxygen, argon and carbon dioxide.
Atom
The atom is the largest entity which remains intact during all chemical
conversion processes.
Basalt
A fine-grained, basic igneous rock consisting mainly of plagioclase feldspar
and pyroxene. Basalts occur principally in lava flows and constitute over
90 per cent of volcanic rocks. Smith (1981)
Basaltic lava
See Basalt
Bathymetry
The measurement of the depth of the ocean floor from the water surface;
the oceanic equivalent of topography. Allaby and Allaby (1990)
Bedrock
The solid rock underneath superficial formations. Chambers (1994)
Biogenic processes
Processes of living, or once-living, organisms. Allaby and Allaby (1990)
Biogenous
Produced by the action of living organisms. Allaby and Allaby (1990)
Biosphere
The zone of air, land, and water (both in lakes and in the sea) at the
surface of the earth that is occupied by organisms.
Carbon dioxide
A colourless, odourless gas at normal temperatures, composed of one atom
of carbon and two of oxygen. It makes up about 0.03% of the atmosphere
by weight. Carbon dioxide is consumed in photosynthesis by green plants
and produced by the respiration of plants and animals and the burning
of fossil fuel.
Carbonate
A mineral containing the chemical group CO3 e.g. calcite (CaCO3). Carbonates
are associated mainly with limestone and dolomite. Allaby and Allaby (1990)
Carbonic acid
A very weak acid formed from carbon dioxide and water. Sharp (1990)
Cation
A positively charged ion from an ionic bonded compound (e.g. Li+).
Charged ions
Atoms, or groups of atoms, which have gained or lost one or more electrons,
and thus carry a negative or positive charge.Abercrombie, Hickman and
Johnson (1980)
Chemical weathering
The process whereby a rock fabric is changed, mainly through the chemical
action of acids (natural and/or anthropogenic) in rain water. These processes
include mineral oxidation, acid hydrolysis, and dissolution. Chemical
weathering may remove the whole rock (as in limestone where the rock is
taken into solution), or may change the chemical composition of the rock
by preferentially removing some minerals holding the particles within
a rock together. Other processes, such as wind action, can then erode
the particles.
Clay
The clay minerals consist of hydrated aluminium silicates that are fine
grained and have layered structures with platy habits.
Clay fraction
The clay part of the soil.
Closed system
With reference to box modelling. A system (e.g. the earth’s crust)
which is considered as having no interaction with other systems (e.g.
the mantle) for the convenience of the model.
Coagulates
With reference to soils: having a semi-solid or clotted structure. Chambers
(1994)
Colloidal
See Colloids
Colloids
A substance in a state which, though apparently dissolved, cannot pass
through a membrane. Chambers (1994)
Compressional waves
(Also called a P-wave) The fastest of the seismic waves travelling away
from a seismic event through solid rock, and consisting of a train of
compressions and dilations of the material. Press and Siever (1982)
Continental crust
The buoyant, light component of the crust which forms the continental
section of a plate.
Continental shelf
The part of a continent which is submerged beneath the sea to a maximum
depth of 200m
Core
The central part of the Earth below a depth of 2900km. It is thought to
be composed of iron and nickel, and to be molten on the outside with a
central, solid inner core. Press and Siever (1982)
Covalent bond
Chemical bonding which occurs by electron sharing.
Crust
The cool, outermost layer of the earth's surface that floats on the plastic
layers beneath.
Crystallization
The formation of matter into a crystal structure.
Decomposition
The breakdown of complex organic material, undertaken by bacteria and
fungi. Leads to the production of humus.
Deposition
The act or process of depositing sediment. Chambers (1994)
Deserts
Areas receiving less than 25cm of rain a year. The term is more generally
applied to any arid area. Deserts do not necessarily have a hot climate:
cold deserts do occur.
Dipole
A body or system (e.g. a water molecule) containing two opposite electric
charges or magnetic poles set a small distance apart. Chambers (1994)
Dissolution
The process by which ionic bonds in a solid are broken and the resulting
ions liberated into water. For example, the removal and weathering of
limestone by the solution of calcium carbonate, its main component.
Earthquake
A quaking or shaking of the earth. May be caused by tectonic processes,
volcanic activity or induced explosions (e.g. bomb testing). Chambers
(1994) Allaby and Allaby (1990)
Ecosystem
A specific biological community and its physical environment interacting
in an exchange of matter and energy.
Elements
A substance which cannot be further divided by chemical methods. The basic
substances which build up chemical compounds. Sharpe (1990)
Erosion
The process of wearing away the land surface, by processes which transport
rock debris. Erosion frequently refers to the loss of soil due to wind
or as a result of washing away by water.
Essential elements
With reference to nutrition: elements necessary for the survival of the
organism.
Essential nutrients
See Essential Elements.
Exudates
Exuded matter. Discharged through pores or incisions. Chambers (1994)
Fault
Cracks or breaks in the earth's crust caused by stresses usually acting
upon the brittle lithosphere. Faults can be small and harmless but they
may also be potentially catastrophic: the San Andreas Fault in California
currently threatens the lives of millions.
Fertility
The reproductive performance of an individual or population, measured
as the number of viable offspring produced per unit time. Lawrence (1995)
Flood plain
The part of a river valley that is made of unconsolidated, river-borne
sediment, and periodically flooded. Allaby and Allaby (1990)
Fossil fuel
A fuel derived from the remains of ancient plant or animal life. The main
forms used are oil, gas and coal.
Gel
A jelly-like, apparently solid colloidal solution. The opposite of sol.
Chambers (1994)
Geological time
Time before written history, divided into epochs in each of which one
of the great rock systems was formed. Chambers (1994)
Granite
A light coloured, coarse-grained, igneous rock, consisting principally
of quartz (at least 20%), alkali feldspar and mica. Allaby and Allaby
(1990)
Gypsum
A calcium sulphate mineral normally found in clays, limestone and sea
water.
Heterogeneous
Variable in composition at different locations, usually because mixing
processes are slow and inefficient.
Horizons
With reference to soils: A horizontal layer that can be distinguished
from the layers below and above it. Identified by a coding system using
a capital letter, sometimes followed by a subscript, such layers are used
to diagnose soil types. Allaby and Allaby (1990)
Hot springs
A continuous flow of hot water through a small opening on to the earth’s
surface. The water is usually groundwater heated at depth by hot rocks
and recycled to the surface by convection. Hot spring waters are rich
in dissolved minerals which are often precipitated around the spring mouth.
Allaby and Allaby (1990)
Humus
Sticky, brown insoluble residue from the bodies of dead plants and animals.
Humus gives soil its structure, coating mineral particles and holding
them together. It also serves as a major source of plant nutrients.
Hydration
Combined with, or having absorbed, water. Chambers (1994)
Hydrogenous
Material derived from inorganic precipitation from seawater.
Hydrosphere
The total body of water of the earth, i.e. the oceans, rivers, lakes,
underground and atmospheric water.
Hydroxides
Compounds containing inorganic OH- groups. Sharp (1990)
Igneous rocks
One of the three main groups of rock types, igneous describes rocks that
have crystallized from a magma. Allaby and Allaby (1990)
Inorganic
With reference to chemistry: of, or relating to, compounds which do not
contain carbon. Also: not of animal or vegetable origin. Chambers (1994)
Ionic charge
Represents the number of electrons lost or gained by an atom, or group
of atoms. If the ion has more electrons than protons, it is negatively
charged, and the number (n) of excess electrons or protons is represented
by ‘n-’ and ‘n+’ respectively (e.g. a hydroxyl
ion is OH-, a calcium ion is Ca2+ ).
Ionic potential
Ionic charge divided by ionic radius.
Ionic radius
The distance from the centre of an ion to the outermost electron(s). Negative
ions have a greater radius, and positive ions a smaller radius, than the
corresponding atom.
Ionic-bonded
Chemicals bonded by electron transfer.
Ions
Atoms or molecules that have acquired an electric charge by the loss (cation;
positive charge) or gain (anion; negative charge) of one or more electrons.
Allaby and Allaby (1990)
Leaching
The removal and transport of elements in solution from and through a soil.
Lithogenous
Material originating from land or undersea volcanic material. Text
Lithosphere
The rigid uppermost portion of the mantle plus the overlying crust of
the earth comprising surface rocks.
Litter
Accumulation of dead plant remains on the soil surface. Allaby and Allaby
(1990)
Mantle
A hot, pliable layer of rock that surrounds the earth's core and underlies
the cool, outer crust.
Metabolism
The total of all the chemical reactions that occur within a living organism.Allaby
(1994)
Metamorphic rock
An aggregate of minerals formed by the recrystallization of pre-existing
rocks in response to a change of pressure, temperature, or volatile content.Allaby
and Allaby (1990)
Metamorphism
The method by which changes are brought about in the earth's crust by
the agencies of heat, pressure and chemically active fluids.
Meteorites
Small, extraterrestrial bodies, most of which probably originate in the
asteroid belt, that enter the Earth’s atmosphere and land on the
surface. Most are only a few centimetres in size. Allaby and Allaby (1990)
Mid-Ocean Ridge
Mid-ocean ridges are located on the ocean floor on the dividing edge between
two plates of the earth's crust which are moving apart. They are associated
with submarine volcanic activity which adds new crustal material to the
edges of the diverging plates.
Mineral oxidation
The addition of oxygen or the removal of electrons from a mineral's component
elements. Associated with the breakdown of the mineral structure and therefore
its resistance to weathering.
Minerals
Naturally occurring homogenous inorganic substances of definite composition
and crystal structure.
Mud flats
Area of a coastline where fine-grained silt or sediment and clay is accumulating.
Its development is favoured by ample sediment, by sheltered conditions,
and by the trapping effect of vegetation. Allaby and Allaby (1990)
Nutrients
Any substance that organisms take in and use for growth and maintenance.
Oceanic crust
The heavy crustal plate which underlies the oceans.
Organic matter
Substances formed by living organisms, often the product of their decay.
Organically Active layer
That part of the soil subject to biological activity.
Oxidation
Oxidation corresponds to the loss of electronegativity.(See also Oxidant).
Oxidised
To combine with oxygen. Also means to lose electrons. Chambers (1994)
Parent material
The original material which gave rise to the one in question.
Particulate material
Made up of small particles.
Physical weathering
Erosion of rock by physical weathering processes, such as temperature
and pressure. Text
Plate boundary
The margin of one of the plates that form that form the upper layer, or
lithosphere, characterized by a combination of tectonic and topographic
features. Allaby and Allaby (1990)
Plate margin
See Plate Boundary.
Plate tectonics
The unifying concept that has drawn continental drift, sea-floor spreading,
seismic activity, crustal structures and volcanic activity into a coherent
model of how the outer part of the earth evolves. Allaby and Allaby (1990)
Plates
A segment of the lithosphere, which has little volcanic or seismic activity,
but is bounded by almost continuous belts (known as plate margins) of
earthquakes and, in most cases, by volcanic activity and young mountain
chains. Allaby and Allaby (1990)
Pore space
The total continuous and interconnecting void space in the bulk volume
of soil or rock. Allaby and Allaby (1990)
Pores
A void surrounded completely by soil or rock materials and created by
the packing of mineral and organic particles. Pores can be filled by any
proportion of air or water. Allaby and Allaby (1990)
Precipitation
With reference to the water cycle: Rain, hail, snow etc. Chambers (1994)
Protons
The nucleus of an atom is composed of protons and neutrons. The main characteristic
of the proton is that it carries a positive electrical charge, conventionally
ascribed the value of +1.
Pure water
Water which contains no dissolved ions and consists only of water molecules.
Pyrite
Iron sulphide (FeS2), also known as ‘fool’s gold’. It
is very widely distributed in a great variety of environments. Allaby
and Allaby (1990)
Reduced
Chemical term referring to the addition of electrons, negatively charged
particles, to a molecule or compound. Commonly this occurs through the
addition of hydrogen.
Residual solid phase
The material left behind after the soluble phase has been removed. Text
Respiration
The breakdown of chemicals (food) through oxidation to release energy
for life. The main components of the reaction are water, oxygen and sugars.
Note that nearly all living organisms respire, plants as well as animals.
Rock Cycle
The geologic cycle, with emphasis on the rocks produced; sedimentary rocks
are metamorphosed to metamorphic rocks, or melted to create igneous rocks,
and all rocks may be uplifted and eroded to make sediments, which lithify
to sedimentary rocks. Press and Siever (1982)
Scree slope
A slope on which an accumulation of coarse rock debris, added to by the
weathering and release of fragments e.g. from a cliff face. Allaby and
Allaby (1990)
Sedimentary rock
Eroded material that is deposited from a fluid (usually water, occasionally
air) under surface temperatures and which becomes solidified through the
effects of time, burial, and chemical reactions.
Sedimentation
The deposition of organic materials or minerals by chemical, physical,
or biological processes. Sediments can be transported from their source
to their place of deposition by gravity, wind, water or ice. Time, burial
and chemical reactions convert sediments into solid sedimentary rock.
Seismic waves
A packet of strain energy which travels away from a seismic source (e.g.
an earthquake). Allaby and Allaby (1990)
Shear waves
Also called S-waves, transverse waves. Seismic waves which travel more
slowly than compressional waves (P-waves), and consist of elastic vibrations
transverse to the direction of travel. S-waves cannot penetrate a liquid.
(See Compressional Waves). Press and Siever (1982)
Silicate rocks
Rocks which contain silicates, the most abundant group of rock-forming
minerals, which can be classified according to the structural arrangement
of the fundamental SiO4 tetrahedra, which are the main building blocks
of the group. Allaby and Allaby (1990)
Sol
A colloidal suspension in a liquid. The opposite to gel. Chambers (1994)
Soluble species
A chemical species capable of being solved, dissolved or resolved.Chambers
(1994)
Subducting plate
A lithospheric plate which is in the process of being consumed at a convergent
plate margin. Allaby and Allaby (1990)
Subduction Zones
Regions where one section of a lithospheric plate is forced beneath an
adjoining plate. Associated with deep trenches in the earth's crust, they
are responsible for the removal of crust by forcing it into the mantle
beneath.
Talus cone
A deposit of large angular fragments of physically weathered rock, usually
at the base of a cliff or steep slope. Press & Siever (1982)
Tectonic processes
Relating to structural changes in the earth’s crust caused by upheavals
and other movements within it. Chambers (1994)
Temperate regions
The parts of the earth of moderate temperature, between the tropics and
the polar circles. Chambers (1994)
Topography
The detailed study, description or feature of a limited area. With reference
to land or the ocean bottom: a description of relief. Chambers (1994)
Trench
With reference to the ocean floor: an elongate depression which runs parallel
to the trend of adjacent volcanic islands or continent. Oceanic trenches
are up to 11km deep, typically 50-100km wide, and may be thousands of
km long. Most are associated with subduction zones.Allaby and Allaby (1990)
Valency
Used to designate the number of bonded neighbour atoms. Sharp (1990)
Velocity
Rate of motion (distance per unit time) in a stated direction. Chambers
(1994)
Vents
Openings or appertures, e.g. volcanic vents. Chambers (1994)
Volcanic activity
The process by which a volcano expels gases and particulate material.
Large clouds (as at Mount St Helens) can result with or without the production
of lavas (as at Mount Etna).
Volcanic islands
Islands produced by magma emanating from volcanic vents in the ocean crust.
Volcanism
All the processes associated with the transfer of magma and volatiles
from the interior of the earth to its surface. Allaby and Allaby (1990)
Water retention
Water holding capacity.
Weathering
The process by which rocks are broken down and decomposed by the action
of external agencies such as wind, rain, temperature changes, plants,
and bacteria. Note that the process acts in situ with no transportation
taking place and is therefore different from erosion. Two forms of weathering,
chemical and physical, can take place and both may act at the same time.