Geoscience Reference
In-Depth Information
Quaternary
Ma
0
Alpine
unconformity
Neogene
Paleogene
Caledonian front
100
Cretaceous
Cimmerian
unconformity
Jurassic
200
Triassic
Permian
Variscan Orogeny
Laurentian
crust
300
Carbon-
iferous
Site of former
lapetus Ocean
Caledonian Orogeny
Devonian
400
Avalonian/
Gondwanan
crust
Silurian
Ordovician
Grampian Orogeny
500
Cambrian
Avalonian
Orogeny
Caledonian Front
600
Proterozoic
Variscan Front
700
Knoydartian
Orogeny
Site of former Rheic-
Rhenohercynian oceans
Complex
sedimentary
igneous and
metamorphic
history
Archaean
Northern
(Laurentian)
Britain &
Ireland
Southern
(Gondwanan)
Britain &
Ireland
Figure 10.21
Major tectono-stratigraphic units in Britain and Ireland, with their current distribution. The separate origin of
developing 'British' crust in northern and southern hemispheres is shown in twin columns, prior to their welding along the Iapetus
Suture in the Caledonian Orogeny.
Source: Woodcock and Strachan (2000).
generation and cooling which progressively refine our
planet's constituent parts. Some processes are necessarily
familiar to us - the weathering of simple nutrients from
more complex rocks, the evaporation of H
2
O from ocean
solutions, the abstraction and reformation of carbon,
hydrogen and oxygen from a variety of sources to form
living cells and even the segregation of different isotopes
of these fractionates (
14
C,
16
O,
18
O, etc.). All require energy,
and the nature and rate of their reactions are also
determined by temperature and pressure.
CONCLUSION
Earth is of almost unimaginable age and yet its modern
character and geological processes can be traced directly
to its astronomic origins. Many geological processes are
imperceptibly slow, measured against our own life spans,
but earthquakes and volcanic eruptions are sharp
reminders of Earth's relentless evolution. The accretion of
a cocktail of planetary matter over 4·6 Ga ago set in train
enduring processes of
chemical fractionation,
heat
