GeologyRocks

Mineral

A naturally occurring homogeneous solid with a highly ordered lattice and of a defined chemical composition.

Mohorovičić discontinuity

The Mohorovičić discontinuity, usually referred to as the Moho, is the boundary between the Earth's crust and the mantle. The Moho serves to separate both oceanic crust and continental crust from underlying mantle. The Mohorovičić discontinuity was first identified in 1909 by Andrija Mohorovičić, a Croatian seismologist, when he observed the abrupt increase in the velocity of earthquake waves (specifically P-waves) at this point.

Neosome

A geometric element of a composite rock or mineral deposit, appearing to be younger than the main rock mass, for example the leucosomes in a migmatite are a neosome.

Nonconformity

An unconformity that exists between sedimentary rocks and metamorphic or igneous rocks when the sedimentary rock was deposited on the pre-existing, eroded metamorphic or igneous rock.

Ordovician

The second period of the Palaeozoic. Spans 510-443. The Ordovician is famous for its graptolite and trilobite-rich deposits, particularly in the UK. The Ordovician ended in a mass extinction, probably caused by an Ice Age.

Palaeozoic

Era comprising the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian, spanning 545-245Ma. The Paleozoic started with an apparent evolutionary burst (the Cambrian Explosion) and ended with the largest mass extinction seen on this planet, the P-T event.

Period

A second order geological time unit.

Permafrost

Soil, rock and sediment where the temperature stays below 0°C for at least two consecutive winters and the summer in between. Permafrost usually occurs in a layer some distance beneath the topsoil.

Permian

The final period of the Palaeozoic from 290Ma-245Ma. The end of the Permian saw a mass extinction that wiped out around 90% of all marine life and nearly 70% of terrestrial life. Many theories have been presented for the cause of the extinction, including plate tectonics, an impact event, a supernova, extreme volcanism, the release of frozen methane hydrate from the ocean beds to cause a greenhouse effect, or some combination of factors.

Epochs:

• Zechstein 260-245Ma
• Rotliegendes 290-260Ma

Plate Tectonics

Plate tectonics is the underpinning theory used in geology. Developed in the late 20th centuary, plate tectonics explains the location of earthquakes and volcanos, the apparent changes in magnetic pole location and shifts in climate recorded in the geological record across the continents. The theory states that the lithosphere is composed of a series of plates which move around the surface. The plates are created at mid-ocean ridges and destroyed at subduction zones.