Evidence for Continental Drift

• Palaeo-climates, Scotland:

  • rocks here dated 700Ma are Tillites (lithified boulder clay); deposits formed beneath glaciers/ice sheets (suggests Ice Age climate during Pre-Cambrian Scotland + likely UK located near South Pole)
  • Devonian age (380Ma) rocks in Scotland are red-sandstones and breccia-conglomerates rich in iron-oxides; rocks formed in hot desert environments (dunes/wadis) suggests UK had hot/arid climate 380Ma + UK on southern arid belt during Devonian (20$^o$S of equator)
• Palaeo-climates, Carboniferous (345-280Ma):

  • in Carboniferous, UK had hot/tropical climate as drifting from southern hemisphere across equator into northern hemisphere; seas were warm/shallow/tropical favouring growth of coral and extensive deposits of limestone
  • carboniferous swamps dominated by horsetails, ferns, gingkoes and cycads (formed UK coal deposits) + carboniferous rocks rich in carbon (dead vegetation accumulated in tropical swamps)
• Palaeo-climates, Devon/Permian:

  • rocks in Devon of Permian age (260Ma) are well sorted desert sandstones with reddish/brown iron-oxide cement; UK located in northern arid belt (climate similiar to Sahara Desert) + palaeo-wind directions from rocks match north-easterlies
  • UK had hot-arid climate 270Ma (30$^o$N), then UK drifted northwards to current latitute (51-55$^o$N)
• Between 1.9million-10,000yrs ago, UK experience Ice Age climate (Pleistocene Glaciation); evidence in erosional landforms (corries/aretes/V-shaped valleys) + depositional features made of boulder clay (drumlins, terminal/medial/lateral moraines).
• Palaeo-magnetic:

  • magnetite found in basic igneous rocks; as basalt cools, magnetite crystallises/becomes orientated with earth's magnetic field at that latitude + basalt cools below Curie Point (500$^oC$) so magnetic pattern locked in rocks
  • magnetic inclination of magnetite crystals in basalt can be measured; angle is indication of distance from North Pole basalt originally formed at + 'apparent polar wandering curve' constructed by looking at inclination of different aged basalts from same region
• Tectonic Fit (of Mountain Belts across former oceans):

  • Caledonian Fold Mountain Belt forms a linear chain that extends from North America through Canada, into Greenland, UK and Scandinavia; these formed 400-450Ma (following closure of Iapetus Ocean) + fragmented/dispersed on different continents.
  • Sediments from the floor of the Iapetus Ocean were uplifted, folded and faulted as continental collision occured in late Silurian/early Devonian - eg. Caledonian, Hercynian, Appalachian, Cordilleran, Andean, Transatlantic, Tasman, Ouchita, Vrallian and Mauritanide.
• Geological Fit (of opposing Continental Coastlines):

  • areas of geological fit across continents; cratons are areas older than 2000Ma and the same cratons have been found across South America/Africa (suggests part of same land mass 2bn years ago)
  • evidence from Gondwanaland; mesozoic dolerite/precambrian anorthosite of same age found across multiple continents + parts of each continent within limit of Permo-Carboniferous glaciation
• Fossil Distribution:

  • Mesosaurus (crocodile-like reptile that lived during early Permian, 286-258Ma); found only in Southern Africa/Eastern South America (suggests they were joined during early Permian).
  • Cyognathus (extinct Therapid/mammal-like reptile that lived during early-mid Triassic, 250-240Ma); found in South Africa/South America.
  • Lystrosaurus (dominant land vertebrate in early Triassic, 250Ma, around 1m in length); found in Antartica, India and South Africa.
• Fossil Distribution:

  • Glossopteris (leaves 2-30cm + evolved in early Permian becoming dominant species + woody/seed-bearing shrub/tree); found in Australia, South Africa/America, India and Antartica.
  • If continental drift hadn't occured, same organism must have evolved independently on seperate continents (contradicts Theory of Evolution).
• Jig-Saw Fit (of opposing Continental Coastlines):

  • continents around Atlantic Ocean fit together - present day gaps/overlaps can be explained by coastal erosion/deposition, or changes in sea level (eustatic) or land level (isostatic) since continental break up
  • eg. Eastern South American/West African Coastlines + African and Arabian plates fit together if Red Sea closed (<30Ma)
• Glacial Deposits (Permo-Carboniferous Glaciation):

  • if continental drift hadn't occured, ice sheet would have extended from south pole to equator - major glaciation occured during early carboniferous with areas of glacial deposits found in South America/Africa, India, Australia and Antartica
  • areas where ice deposits occur continue across continental boundaries + ice flow directions from glacial striations indicate it spreading from central position in all directions
• • 1.9-0.01Ma: Boulder Clay, Glacial (51-55$^o$N)
  • 270-250Ma: Desert Sandstones/Breccias, Hot desert (20-30$^o$N)
  • 330-300Ma: Limestone/Coral Reefs/Coal, Equatorial (10$^o$N-10$^o$S)
  • 390-410Ma: Desert Sandstones/Breccias, Hot Desert (20-30$^o$S)
  • 700-720Ma: Boulder Clay, Glacial (60-70$^o$S)