Page 61 - Curriculum Visions Dynamic Book. To close the book, close the window or tab.

continental drift: the theory suggested
by Alfred Wegener that earth’s continents were originally one land mass which split up to form the arrangement of continents we see today.
continental shelf: the ocean floor from the coastal shore of continents to the continental slope.
continental shield: the ancient and stable core of a tectonic plate. Also called a shield.
convection: the slow overturning of a liquid or gas that is heated from below.
cordillera: a long mountain belt consisting of many mountain ranges.
core: the innermost part of the earth. The earth’s core is very dense, rich in iron, partly molten, and the source of the earth’s magnetic field. The inner core is solid and has a radius of about 1300 kilometres. The outer core is fluid and is about 2100 kilometres thick. S waves cannot travel through the outer core.
cracking: the breaking up of a hydrocarbon compound into simpler constituents by means of heat.
crater lake: a lake found inside a caldera. craton: see shield.
Cretaceous, Cretaceous Period: the third period of the Mesozoic Era. It lasted from about 135 to 65 million years ago. It was
a time of chalk formation and when many dinosaurs lived.
cross-bedding: a pattern of deposits in a sedimentary rock in which many thin layers lie at an angle to the bedding planes, showing that the sediment was deposited by a moving fluid. Wind-deposited cross-beds are often bigger than water-deposited beds.
crust: the outermost layer of the earth, typically 5km under the oceans and 50 to 100km thick under continents. It makes up less than 1 per cent of the earth’s volume.
crustal plate: see tectonic plate. crystal: a mineral that has a regular
geometric shape and is bounded by smooth, flat faces.
crystal system: a group of crystals with the same arrangement of axes.
crystalline: a mineral that has solidified but has been unable to produce well-formed crystals. Quartz and halite are commonly found as crystalline masses.
crystallisation: the formation of crystals.
cubic: a crystal system in which crystals have 3 axes all at right angles to one another and of equal length.
cuesta: a ridge in the landscape formed by a resistant band of dipping rock. A cuesta has a steep scarp slope and a more gentle dip slope.
current bedding: a pattern of deposits in
a sedimentary rock in which many thin layers lie at an angle to the bedding planes, showing that the sediment was deposited by a current of water.
cyclothem: a repeating sequence of rocks found in coal strata.
delta: a triangle of deposition produced where a river enters a sea or lake.
deposit, deposition: the process of laying down material that has been transported in suspension or solution by water, ice, or wind. A deposit is the material laid down by deposition (e.g. salt deposits).
destructive plate boundary: a line where plates collide and where one plate is subducted into the mantle.
Devonian, Devonian Period: the fourth period of geological time in the Palaeozoic Era, from 395 to 345 million years ago.
diorite: an igneous plutonic rock between gabbro and granite; the plutonic equivalent of andesite.
dip: the angle that a bedding plane or fault makes with the horizontal.
dip slope: the more gently sloping part of a cuesta whose surface often parallels the dip of the strata.
discontinuity: a gap in deposition, perhaps caused by the area being lifted above the sea so that erosion, rather than deposition, occurred for a time.
discordant coast: a coast where the rock structure is at an angle to the line of the coast. See also concordant coastline.
displacement: the distance over which one piece of rock is pushed relative to another.
dissolve: to break down a substance into a solution without causing a reaction.
distillation: the boiling off of volatile materials, leaving a residue.
dolomite: a mineral composed of calcium magnesium carbonate.
dome: a circular, uplifted region of rocks taking the shape of a dome and found in some areas of folded rocks. Rising plugs of salt will also dome up the rocks above them. They sometimes make oil traps.
dormant volcano: a volcano that shows no signs of activity but which has been active in the recent past.
drift: a tunnel drilled in rock and designed to provide a sloping route for carrying out ore or coal by means of a conveyor belt.
dyke: a wall-like sheet of igneous rock that cuts across the layers of the surrounding rocks.
dyke swarm: a collection of hundreds or thousands of parallel dykes.
earthquake: shaking of the earth’s surface caused by a sudden movement of rock within the earth.
element: a fundamental chemical building block. A substance that cannot be separated into simpler substances by any chemical means. Oxygen and sulphur are examples of elements.
eon: the largest division of geological time. An eon is subdivided into eras. Precambrian time is divided into the Archean (earlier than 2.5 billion years ago) and Proterozoic eons (more recent than 2.5 billion years ago).
The Phanerozoic Eon includes the Cambrian Period to the present.
epicentre: the point on the earth’s surface directly above the focus (hypocentre) of an earthquake.
epoch: a subdivision of a geological period in the geological time scale (e.g. Pleistocene Epoch).
era: a subdivision of a geological eon in the geological time scale (e.g. Cenozoic Era). An era is subdivided into periods.
erode, erosion: the twin processes of breaking down a rock (called weathering) and then removing the debris (called transporting).
escarpment: the crest of a ridge made of dipping rocks.
essential mineral: the dominant mineral constituents of a rock used to classify it.
evaporite: a mineral or rock formed as the result of evaporation of salt-laden water, such as a lagoon or salt lake.
exoskeleton: another word for shell. Applies to invertebrates.
extinct volcano: a volcano that has shown no signs of activity in historic times.
extrusive rock, extrusion: an igneous volcanic rock that has solidified on the surface of the earth.
facet: the cleaved face of a mineral. Used in describing jewellery.
facies: physical, chemical, or biological variations in a sedimentary bed of the same geological age (e.g. sandy facies, limestone facies).
family: a part of the classification of living things above a genus.
fault: a deep fracture or zone of fractures
in rocks along which there has been displacement of one side relative to the other. It represents a weak point in the crust and upper mantle.
fault scarp: a long, straight, steep slope in the landscape that has been produced by faulting.
feldspar: the most common silicate mineral. It consists of two forms: plagioclase and orthoclase.
61