| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S |T | U | V | W |

A

Aquifer

An underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) in which groundwater can be stored and usefully extracted using a water bore.

Aquifer Matrix

The underground layer of water-bearing permeable rock or unconsolidated materials which makes up an aquifer.

Aquifer yield

The maximum rate of extraction which can be sustained by an aquifer without compromising key environmental assets or ecosystem functions, or the productive base of the resource.

Andesite

A fine-grained, mafic rock consisting of both mafic minerals and plagioclase, and usually containing quartz.

Anticline

Folded rock layers which are convex upwards with the oldest rocks in its centre, or core, and the youngest rocks on the outside of the structure. It is the opposite of a syncline.

Archean Eon

The interval of geological time from 4 - 2.5 billion years ago and includes the Neoarchean, Mesoarchean, Paleoarchean and Eoarchean Periods. Read more about the international standard timescale at the ICS Timescale [PDF 406KB].

B

Banded iron formation

A chemical sedimentary rock containing at least 15% iron of sediment origin, showing marked banding of iron-rich minerals and chert or quartz.

Basalt

A fine-grained, mafic rock of volcanic origin consisting mainly of the minerals plagioclase, olivine, and pyroxene.

Basaltic lava

A volcanic lava which forms fluid, fast moving flows.

Bathymetry

The study and mapping of seafloor elevations and the variations in water depth to depict the topography of the seafloor.

Benthic

Material or life forms associated with the seafloor or the bottom of a body of water such as a lake.

Bore Yield

The amount of water which can be extracted from a bore (either by pumping or natural artesian flow) over a specific time interval. Bore yields are usually measured in litres per second.

Brackish Water

Water that has more saline content than fresh water, but not as much as seawater. It may result from mixing seawater with fresh water, as in estuaries, or water contained in ancient aquifers.

Breccia

A coarse-grained clastic rock composed of angular broken rock fragments held together by a mineral cement or in a fine-grained matrix. It differs from conglomerate in that the fragments have sharp edges and unworn corners.

C

Calcarenite

A limestone consisting mainly of detrital calcite particles of sand size.

Calcite

A common and widespread mineral with highly variable forms and colours which occurs in many different geological environments.

Calc-silicate rock

A crystalline metamorphic rock formed mainly of calcium-bearing silicate minerals.

Calcrete

A hardened sedimentary deposit of calcium carbonate cemented together with other materials, including gravel, sand, clay, and silt.

Caldera

A crater or surface depression formed when a magma chamber collapses.

Cambrian Period

The interval of geological time from 542 - 488.3 million years ago in the Paleozoic Era. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Carboniferous Period

The interval of geological time from 359.2 million up to 299 million years ago in the Paleozoic Era. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Cenozoic Era

The interval of geological time from 65.5 million years up to the present day in the Phanerozoic Eon. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Chert

A silica-rich, very finely crystalline rock, chert may be of organic or inorganic origin. It occurs as layers or nodules in some sedimentary rocks and is of highly variable colour.

Chlorophyll concentration

A measure of the abundance of algae, also called phytoplankton, which account for most of the plant production in the ocean.

Chronostratigraphic

A term used to describe a body of rock strata formed during a specific interval of geological time.

Cirque

An amphitheatre-like valley which has been formed by erosion at the head of a glacier. The bowl like shape often results in cirques becoming lakes such as the Blue Lake in the Australian Alps near Mount Kosciuszko.

Cisuralian Epoch

The earliest Epoc of the Permian period covering the period from 299 - 270.6 million years years ago. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Clastic

Composed of broken fragments that have been derived from pre-existing rocks by weathering and erosion and transported some distance from their place of origin.

Conglomerate

A clastic sedimentary rock containing relatively large, rounded to subangular fragments (pebbles, cobbles or boulders), set in a fine-grained matrix of sand or silt.

Coordinate grid

Eastings and northings, in metres.

Cordillera

A parallel chain of mountains such as the Great Dividing Range in eastern Australia.

Craton

An ovoid or egg shaped old, stable and strong continental core onto which younger rocks have accumulated.

Cretaceous Period

The interval of geological time from 145.5 - 65.5 million years ago in the Mesozoic Era. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Crystal

A rock with external plane flat, smooth faces and a regularly repeating internal structure. Crystals are formed when a substance solidifies.

D

Dacite

A fine-grained volcanic rock; the extrusive equivalent of granodiorite.

Detrital

Loose material including stone fragments, silt and other regolith material eroded from rocks.

Devonian Period

The interval of geological time from 416 - 359.2 million years ago in the Paleozoic Period. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Diurnal

Associated with a 24 hour period in contrast to the shorter Semi-Diurnal.

Dolerite

A mafic rock, similar in composition to, but finer-grained than, gabbro.

Dolomite

A sedimentary rock consisting mainly of a calcium and magnesium carbonate.

Dunite

A dense, igneous rock composed of at least 90% olivine.

Duricrust

A general term for a hard crust on or near the surface of a soil formed in a semi-arid climate and is made up of material such as calcrete and silcrete.

Dyke

Sometimes spelt dike, it is a vertical pathway formed when magma is injected into fractured rock within the Earth's crust.

E

Earthquake swarms

A sequence of similar sized earthquakes which occur over a localised area in a relatively short period of time. Swarms are recorded most often prior to volcanic eruptions but are associated also with fault systems.

Electrical conductivity

A method of measuring the amount of total dissolved material in water through the use of a sensor consisting of two metal electrodes which provides an estimate of salinity levels.

Eoarchean Era

The interval of geological time from 4 - 3.6 billion years ago in the Archean Eon. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Eocene Epoch

Part of the Paleogene Period, the Eocene Epoc is the interval of geological time from 55.8 - 33.9 million years ago. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Eon

The longest unit of geological time, next in order of magnitude above an Era. Refer to the international standard timescale chart at the ICS Timescale [PDF 406KB].

Ephemeral Lake

A short lived water body which fills periodically and quickly dries up, such as Lake Eyre in South Australia.

Era

A unit of geological time, next in order of magnitude below an Eon. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Evaporite

A non-clastic sedimentary rock composed mainly of minerals produced from a saline solution as a result of extensive or total evaporation.

F

Facies

The features of a distinctive body of rock which forms as a result of sedimentation and reflects a particular process or environment.

Fault Scarp

Geological evidence on the Earth's surface of the displacement of land by the movement of a fault, usually as a result of an earthquake. They often appear as a steep slope or cliff.

Feldspar

A large group of minerals which are the extrusive component of igneous and plutonic rocks as well as many sedimentary and metamorphic rocks.

Felsic rock

Rock dominated by light-coloured minerals such as quartz and feldspar.

Fissure

A fracture or crack in rock along which there is an open pathway for fluids to travel, including lava.

Fumarole

A vent in the Earth's surface from which volcanic gasses and steam are emitted.

Furongian Epoch

The interval of geological time from around 499 - 488.3 million years years ago in the Cambrian period. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

G

Gabbro

A coarse-grained, mafic intrusive rock composed mainly of the minerals plagioclase, pyroxene and olivine.

Geographic graticule

Latitude and longitude, in degrees, minutes and seconds.

Geomorphology

The study of the shape and evolution of landforms and the rocks and processes which form them.

Geosequestration

The geological storage of carbon dioxide injected into deep underground geological formations where it is permanently immobilised by natural processes including physical, dissolution, residual and mineral trapping.

Geothermal gradient

The rate of increase in temperature relating to the depth in the Earth.

Gneiss

A metamorphic rock, commonly rich in quartz and feldspar, with a banded and foliated texture, formed at temperatures above about 550 degrees centigrade.

Granite

An intrusive rock dominated by quartz (10-50%) and alkali feldspar.

Granodiorite

An intrusive rock like granite, but containing a high proportion of plagioclase feldspar and mafic minerals.

Granulite

A metamorphic rock, commonly granular in texture, which has cooled from temperatures above about 700 degrees centigrade.

Guadalupian Epoch

Part of the Permian Period, the Guadalupian Epoc is the interval of geological time scale from 270.6 - 260.4 million years ago. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

H

Hadean Eon

The interval of geological time from the Earth's formation around 4.6 - 4 billion years ago. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Heat pump

A geothermal heat pump uses the relatively constant heat of the Earth to alter the temperature of water circulated underground.

Holocene Epoch

The interval of geological time in the Quaternary Period from around 11 700 years ago to the present day. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Hornblende

A common form of a group of silicate minerals containing varying amounts of calcium, sodium, iron, magnesium, and aluminium. It usually occurs as crystals in granite, schist, gneiss, or basalt.

Hydraulic Head

The water level above a zero datum (usually sea level) which is determined when tapping an aquifer which is open to the atmosphere.

Hydrogeology

The study of the geological factors associated with the Earth's water.

Hydrothermal

Geothermal systems with naturally occurring groundwater which has been heated by either heat-producing rocks or nearby volcanic activity.

I

Inselberg

An isolated rock hill, knob, ridge or small mountain which rises abruptly from a gently sloping or virtually level surrounding plain.

Intrusive rock

Igneous rock crystallised from magma deep in the Earth's crust.

Igneous rock

One of the three principal classes of rocks; metamorphic, sedimentary and those formed by the cooling and solidification of magma.

J

Jurassic Period

The interval of geological time from 199.6 - 145.5 million years ago in the Mesozoic Era. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

K

Karst

A topography shaped by water dissolving a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite. It is frequently associated with caves, dolines (sink holes) and cliffs.

Komatiite

Rocked formed of ultramafic lava, largely restricted to the Archean of Western Australia.

L

Lahar

A rapidly flowing mixture of rock debris and water from a volcano.

Laterite

A highly weathered red subsoil rich in secondary oxides of iron and/or aluminium. Laterite develops in wet-tropical and warm to temperate regions and is a residual product of weathering.

Lava

Molten rock expelled at the Earth's surface by volcanic processes. It also refers to the solidified deposits of such eruptions.

Limestone

A sedimentary rock consisting mainly of the mineral calcite.

Lithology

A subdivision of petrology, a branch of geology that studies rocks and the conditions in which rocks form, lithology focuses on the classification of hand-samples or outcrop-scale description of rocks. This is in contrast to petrography which deals with microscopic details of rocks.

Llandovery Epoch

Part of the Silurian Period, the Llandovery Epoc is the interval of geological time from 443.7 - 428.2 million years ago. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Lopingian Epoch

The interval of geological time from 260.4 - 251 million years years ago in the Permian Period. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Ludlow Epoch

The interval of geological time from 422.9 - 418.7 million years ago in the Silurian Period. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

M

Mafic rock

Rock dominated by dark-coloured minerals such as pyroxene and hornblende.

Magma

Material within the subsurface of a volcano which is derived from molten rock and solid crystalline or residual fragments and volatile gases.

Magnetogram

A chart that shows how elements of the Earth's magnetic field change with time, typically over 24 hours, at a given location. Read more at Data and Reports - Geomagnetism.

Magnetometer

An instrument used to measure the strength and/or direction of a magnetic field.

Magnetosphere

The region of space around a planet which is influenced by that planet's magnetic field.

Magnetotelluric

A geophysical technique in which components of the Earth's electrical and magnetic fields are measured simultaneously at various frequencies.

Magnitude scale

The magnitude is a way of measuring the size of an earthquake from measurements of shaking made on a seismograph. Magnitude scales are logarithmic, meaning that a magnitude 6.0 has a shaking amplitude 10 times larger than 5.0. In terms of energy, a 6.0 releases about 32 times more energy than a 5.0. The first magnitude scale developed was the Richter or local magnitude scale. Other magnitude scales such as the surface wave, body wave, and moment magnitude scales determine the size of the earthquake using different methods. See also Moment Magnitude Scale.

Mantle

A layer measuring about 2900 kilometres thick which separates the Earth's crust and its core.

Marble

A metamorphic rock which has been formed from limestone or dolomite.

Mesoarchean Era

The interval of geological from 3.2 - 2.8 billion years ago in the Archean Eon. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Mesozoic Era

The interval of geological time from 251 - 65 million years ago in the Phanerozoic Eon. Read more about to the international standard timescale chart at the ICS Timescale [PDF 406KB].

Mesoproterozoic Era

The interval of geological time from 1.6 - 1 billion years ago during the Phanerozoic Eon. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Metamorphic rock

Metamorphic rock is created in a process which takes place when the heat and pressure deep in the Earth's crust cause rocks to change their original mineral compositions and textures. The resulting metamorphic rocks can form from igneous, sedimentary or older metamorphic rocks.

Metamorphic Complex

The metamorphic rocks constituting a whole group closely related on a regional and/or stratigraphic basis.

Metasediment

A metamorphic sedimentary rock which shows evidence of having been subjected to metamorphism (see metamorphic rock) and deformation.

Miocene Epoch

The interval of geological time from 23.03 - 5.332 million years ago in the Neogene Period. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Moho

The Moho, or Mohorovicic discontinuity, marks the goeophysical boundary between the Earth's crust and the mantle.

Moment Magnitude Scale

The moment magnitude scale characterises the size of an earthquake in terms of its energy release, which scientists call its seismic moment. The seismic moment relates to the area and the average slip of the rupture along a fault surface. The advantage of the moment magnitude scale over other magnitude scales is that, it remains accurate for very large magnitude earthquakes and can be used for earthquakes of any size. The moment magnitude scale is the preferred magnitude scale used by seismologists today. See also Magnitude Scale.

Monocline

A one-sided flexure in layers of rock which are usually horizontal except in the flexure itself which results in a step-like zone of steeper dip within an otherwise horizontal or gently-dipping sequence. See also anticline and syncline.

Mudstone

A fine-grained sedimentary rock consisting mainly of clay mineral particles.

N

Nadir

The point on the Earth's surface which is immediately below a remote sensing instrument. If you are standing at the NADIR point of a satellite observation the satellite will be directly overhead.

Nautical mile

One nautical mile is internationally defined as 1.852 kilometres.

Neoarchean Era

The interval of geological time from 2.8 - 2.5 billion years ago in the Archean Eon. Read more about the international standard timescale at the ICS Timescale [PDF 406KB].

Neogene Period

The interval of geological time from 23.03 - 2.588 million years ago in the Cenozoic Era. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Neoproterozoic Period

The interval of geological time from one billion to 542 million years ago in the Proterozoic Eon. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Norite

An intrusive rock similar to gabbro but containing an orthopyroxene (hypersthene) as the dominant mafic mineral.

O

Olivine

A mineral consisting of magnesium iron silicate.

Oligocene Epoch

Part of the Paleogene period, the Oligocene Epoc covers the interval of geological time from 33.9 - 23.03 million years ago. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Ordovician Period

The interval of geological time from 488.3 - 443.7 million years ago in the Paleozoic Era. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Orogen

A generally elongate package of rocks which have been deformed by compressional forces. These forces induce folding and faulting which commonly result in mountain building such as the Himalayas.

Orogeny

A period of mountain-building.

Outcrop

A term designating the exposed surface of rock layers which have not decomposed.

Orthogneiss

A metamorphic igneous rock formed by deformation and usually some re-crystallisation of an igneous rock.

P

Paleoarchean Period

The interval of geological time from 3.6 - 3.2 billion years ago in the Paleogene Period. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Paleocene Epoch

The interval of geological time from 65.5 - 55.8 million years ago in the Paleogene Period. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Palaeochannel

An ancient, inactive river or stream channel system which has been filled with sediments and may have been covered with regolith.

Paleogene Period

The interval of geological time from 65.5 - 23.03 million years ago in the Cenozoic Era. Read more on the international standard timescale chart at the ICS Timescale [PDF 406KB].

Paleoproterozoic Era

The interval of geological time from 2.5 - 1.6 billion years ago in the Proterozoic Eon. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Palaeovalley

Like palaeochannels, palaeovalleys are geologically ancient river valleys which no longer function as active surface water systems. Although surface water no longer flows in most palaeovalleys, the sediments which have filled in the river channels commonly form good quality aquifers which are capable of transmitting significant quantities of groundwater.

Paleozoic Era

The interval of geological time from 542 - 251 million years ago in the Phanerozoic Eon. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Period

A geological time subdivision of an Era, during which the rocks of the corresponding system were formed.

Peridotite

A mafic igneous rock consisting mainly of the minerals of olivine and pyroxene.

Permian Period

The interval of geological time from 299 - 251 million years ago in the Paleozoic Era. Read more on the international standard timescale chart at the ICS Timescale [PDF 406KB].

Petrography

A branch of geology which focuses on the detailed, microscopic study of rocks to analyse and describe their mineral content and geological make up.

Petrology

The branch of geology which studies rocks and the conditions in which rocks form.

Phanerozoic Eon

The interval of geological time from 542 million years ago to the present day. Read more on the international standard timescale chart at the ICS Timescale [PDF 406KB].

Phonolite

A fine-grained alkaline volcanic rock, primarily composed of alkali feldspar and feldspathoid minerals.

Phyllite

A metamorphic rock, intermediate in grade between slate and mica schist.

Pillow basalt

These structures form when lava is extruded into water and derive their name from the rounded shape caused by the cooling process.

Pipe

A vertical conduit in the Earth's crust through which magma has passed. Pipes are often formed during explosive events and are commonly associated with diamonds.

Plagioclase

A group of feldspar minerals which are the extrusive component of igneous, plutonic and metamorphic rocks as well as many sedimentary rocks.

Pleistocene Epoch

The interval of geological time from 2.588 million to 11 700 years ago in the Quaternary Period. Read more on the international standard timescale chart at the ICS Timescale [PDF 406KB].

Pliocene Epoch

The interval of geological time from 5.332 - 2.588 million years ago in the Neogene Period. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Plutonic rock

An igneous rock which cooled and solidified below the Earth's surface in contrast to volcanic rock which cools above ground.

Porphyritic

An environment with rocks containing large crystals in fine grained material which has been formed below the Earth's surface.

Potentiometric surface

The level to which water in a confined aquifer would rise if unaffected by pressure from the surrounding rocks and sediments.

Pridoli Epoch

Part of the Silurian Period, the Pridolian Epoc covers the interval of geological time from 418.7 - 416 million years ago. More informationis avialble at the international standard timescale chart at the ICS Timescale [PDF 406KB].

Proterozoic Eon

The interval of geological time from 2.5 billion to 542 million years ago. Read more at the international standard timescale chart at the ICS Timescale [PDF 406KB].

Pumice

A volcanic rock which is full of small enclosed cavities or gas bubbles formed when large volumes of gases expand within a volcano and then quickly cool as they near the surface.

Pyroclastic flows

An avalanche of hot rocks and gases moving away from a volcano at elevated temperatures and high speed.

Pyroxene

A group of dark green, brown, or black crystalline silicate minerals common in igneous and metamorphic rocks.

Pyroxenite

An ultramafic intrusive rock, chiefly composed of the mineral pyroxene.

Q

Quartz

The second most abundant mineral in the Earth's crust after feldspar, quartz forms in a variety of geologic environments and is a common constituent of granite, sandstone and many other igneous, sedimentary, and metamorphic rocks. It is often associated with veins and fractures and his host to other minerals such as copper, gold, tin, tungsten and antimony.

Quartzite

A crystalline rock formed mainly of quartz.

Quasar

Quasars (QUASi-stellAR radar sources) are gigantic, very energetic galaxies which emit electromagnetic energy, including radio waves and are used in geodesy to realise coordinate systems.

Quaternary Period

The interval of geological time from 2.588 million years ago to the present day in the Cenozoic Era. Read more in the international standard timescale chart at the ICS Timescale [PDF 406KB].

R

Radiogenic

The heat and isotopes produced as a result of the decay of uranium in the Earth's crust.

Regolith

The layer or mantle of fragmental and unconsolidated rock material which covers the Earth's bedrock.

Rhyolite

A volcanic rock with a high silica content which is created from very fluid, slow moving lava that creates a layered structure.

S

Salinity

The amount of materials dissolved in water or salts present in the soil with measurements usually expressed in terms of parts per million, milligrams per litre or electrical conductivity.

Salinisation

The accumulation of soluble salt within the soil, which increases as groundwater evaporates and salts concentrate in the soil.

Sandstone

A clastic sedimentary rock composed of fragments of sand, set in a fine-grained matrix of silt or clay.

Scalar quantity

A scalar quantity is something which only has a measurable magnitude, or strength. Temperature is an example of a scalar quantity because it has a measurable magnitude but not a direction. In contrast, a vector quantity has both a magnitude, or strength, and direction.

Schist

A crystalline metamorphic rock which can be readily split into thin flakes or slabs because of a strong foliation of the constituent minerals.

Scoria

A volcanic rock formed when large volumes of gases expand within a volcano and then quickly cool as it nears the surface to create a rock with numerous small cavities.

Sediment

Formed from the collection of materials transported by water, wind or ice, or deposited by organisms.

Sedimentary rock

Rock formed from the consolidation of sediments.

Seismic waves

Seismic waves are generated by earthquakes and volcanoes as well as sythically during seismic surveys when an instrument sends an acoustic pulse into the Earth's crust and measures distances in terms of the time it takes an echo of the pulse produced to return to sensors. Analysis of the results provides information on the geological profile at various depths. Seismic waves generated by earthquakes and volcanoes are measured on a seismograph.

Seismograph

An instrument which measures and records motions of the ground, including those generated by earthquakes, nuclear explosions and other seismic sources, allowing seismologists to locate and measure the size of these different events.

Semi-Diurnal

Occurring approximately once every 12 hours in contrast to the longer Diurnal.

Serpentinite

A rock consisting almost wholly of serpentine-group minerals, derived from the alteration of mafic minerals such as olivine and pyroxene.

Shale

A fine-grained sedimentary rock formed by the consolidation of clay or mud.

Shield Volcano

A broad, low relief volcano with shallow-sloping sides which are built by highly fluid lavas, sometimes travelling long distances across slight inclines to create a relatively flat, broad profile.

Silcrete

A hardened soil duricrust which is formed when silica is dissolved and resolidifies as a cement. It is common in arid regions of Australia.

Silica

Is an oxide of silicon.

Silicate

Is any mineral which has its basic structure based on silicon, or any salt derived from silia or one of the silicic acids.

Silicon

Is the most abundant element in the Earth's crust, making up 25.7% of the crust by mass.

Siltstone

A sedimentary rock similar in composition to mudstone, but slightly coarser grained.

Silurian Period

The interval of geological time from 443.7 - 416 million years ago in the Paleozoic Era. Read more about the international standard timescale chart at the ICS Timescale [PDF 406KB].

Slate

A compact, fine-grained metamorphic rock which is generally formed from shale and splits into slabs and thin plates.

Solar-terrestrial relationship

The solar-terrestrial relationship refers to the influence of the sun on the Earth. The effects of solar activity, such as sun spots and solar flares, travel through the solar system via the solar wind. Interaction between the solar wind and the Earth's magnetic field has a significant influence on the Earth's geomagnetism. At times of high solar activity auroras are often seen near the magnetic poles as particles in the solar wind travel through the polar atmosphere.

Sonar

A name derived from the phrase 'sound navigation and ranging' it is the equipment and the method used to determine, by underwater sound, the depth of and the presence, location or nature of objects in the sea, as well as the character of the seafloor.

Stratigraphic unit

A body of adjacent rock strata recognised as a unit in the classification of a rock sequence with respect to any of the many attributes that rocks may possess.

Stratotectonic

A term used to describe tectonic evolution in relation to stratigraphy.

Subduction Plate margins

Areas at the edge of two tectonic plates where one plate is being forced beneath another. Subduction margins are generally characterised by a deep-sea trench.

Subduction zone

A subduction zone is a place where one tectonic plate sinks below another plate and moves into the mantle.

Supergroup

An assemblage of related rock groups which comprise a number of rock formations and have significant lithological features in common.

Surficial

Unconsolidated geologic materials lying on top of the bedrock. Also referred to as Quaternary geology.

Suture

A suture in structural geology is a major fault zone through an orogen or mountain range. Sutures separate terranes as well as tectonic units which have different plate tectonic and metamorphic and paleogeographic histories.

Swath

The strip of land which a satellite can observe as it traverses around the Earth. The swath-width is the distance across that strip. Swath-widths can vary from a few kilometres to thousands of kilometres.

Syenite

An intrusive rock containing alkali feldspar, with minor plagioclase and mafic minerals and little quartz. It is similar to granite, but less quartz-rich.

Syncline

A downward-curving fold, with rock layers which are concave upward and have the youngest rocks in the centre of the formation and the oldest rocks on the outside. It is the opposite of an anticline.

T

Tectonic plates

A massive, irregularly shaped slab of solid rock which makes up both continental and oceanic areas of the Earth's crust.

Tephra

Any airborne volcanic material ejected during explosive volcanic activity.

Terreneuvian Epoch

The interval of geological time from 542 to about 521 million years ago in the Cambrian Period. Read the international standard timescale chart at the ICS Timescale [PDF 406KB].

Theodolite

An instrument used in surveying and engineering applications for measuring both horizontal and vertical angles.

Thermal conductivity

A measure of the ability of a substance to conduct heat.

Tillite

A sedimentary rock formed from consolidation of glacial drift (till), which is deposited directly by and underneath a glacier, and consists of a heterogeneous mixture of clay, silt, sand, gravel and boulders.

Tonalite

An intrusive rock likegranodiorite, but containing less quartz (20-60%) and plagioclase feldspar well in excess of alkali feldspar.

Trachybasalt

A volcanic rock intermediate in composition between trachyte and basalt.

Trachyte

A fine-grained porphyritic volcanic rock, consisting mainly of alkali feldspar and minor mafic minerals; the extrusive equivalent of syenite.

Triassic Period

The interval of geological time from 251 - 199.6 million years ago in the Mesozoic Era. Read the international standard timescale chart at the ICS Timescale [PDF 406KB].

Tuff

A volcanic rock composed of compacted volcanic ash.

U

Ultramafic rock

An igneous rock composed chiefly of mafic minerals, such as dunite, peridotite and pyroxenite.

Unconformity

A break or gap in the geologic record where a rock unit is overlain by another which is not of the same age.

V

Vector quantity

A vector quantity is something that has a measurable magnitude, or strength, and direction. For example, the Earth's magnetic field is a vector quantity because both its strength and direction can be measured. In contrast, a scalar quantity has only a magnitude, or strength.

Volcanic rock

Igneous rock created as a result of volcanic eruptions after magma has reached the Earth's surface.

W

Wavelength

The distance over which the wave shape (peak or trough) repeats.

Wenlock Epoch

Part of the Silurian Period, the Wenlock Epoc covers the Earth's geological time scale from 428.2 - 422.9 million years ago. Read more at the international standard timescale chart at the ICS Timescale [PDF 406KB].