Continental drift theory of Taylor
- B .Taylor postulated his concept of horizontal displacement of the continents in 1908.
- The main purpose of his hypothesis was to explain the problems of the origin of the folded mountains of tertiary period.
- The concept of Taylor is considered to be the first attempt in the field of continental drift, though Antonio Snider presented his views about drift in the year 1858 in France.
- According to him there were two land masses during Cretaceous period.
- Lauratia and Gondwanaland were located near the north and south pole respectively.
- The continent were made of sial which was practically absent in the oceanic crust.
- Continent moved towards the equator, the main driving force of the continental drift was tidal force.
- Continents were displaced in two ways:
(i) Equator wards movement
(ii) Westward movement
- Lauratia started moving away from the north pole because of enormous tidal force of the moon towards the equator in a radial manner.
- This movement of landmass resulted into tensional force near the north pole which caused stretching, splitting and rupture in landmass.
- The displacement of the Gondwana land from the South Pole towards the equator caused splitting and disruption.
- Arctic sea was formed between Greenland and Serbia due to earthward movement of Lauratia.
- Atlantic and Indian Ocean were supposed to have been formed because of filling of gaps between the drifting continents with water.
- Taylor assumed that the landmasses began to move in the lobe form while drifting through the zones of lesser resistance.
- Thus mountain and island arcs were formed in the frontal part of the moving lobes.
- The Himalayas. Caucasus and Alps are considered to have been formed during equator ward movement of the Lauratia and Gondwanaland from the north and south poles respectively
- The Rockies and Andes formed due to westward movement of the landmasses.
- Taylor’s main aim was to explain the origin of the tertiary folded mountains and hence he made the continents to move at a very large scale.
- He described displacement of the landmasses for thousands of kilometres, but displacement of landmasses up to 32-64 Km would have been sufficient enough for the purpose.
- Tidal force was used as mode of displacement , if it was so enormous during cretaceous period that it could displace the landmasses for thousands of kilometres
- Apart then it might have also put a break on the rotatory motion of the earth and thus rotation of the earth might have been stopped within a year.
- Though the concept of F.B. Taylor is not acceptable but his hypothesis is considered to be significant on the ground that
- He raised his voice very forcefully through deductive postulation against the prevalent concept of the permanency of the continents and ocean basins.
Plate tectonic theory
- It was a great scientific achievement of the decade of 1960s; it is based on the two major scientific concepts
(i) The concept of continental drift
(ii) The concept of sea – floor spreading
- Lithosphere is internally made of rigid plates (first used by Canadian geophysicist J.T. Wilson in 1965), six major plates and 20 minor plates have been identified so far.
- Six major plates are Eurasian plate, Indian – Australian plate, American plate, Pacific plate, African plate and Antarctic plate.
- J.Morgan and Le Pichon elaborated the various aspects of plate tectonics in 1968
- Now the continental drift and the displacement are considered a reality on the basis of plate tectonics.
- Tectonic plate boundaries are most important because all tectonic activities occur along the plate margins.
Fig- Main aspects of plate tectonics
Plate margins are generally divided into three groups
Constructive plate margins
- These are also called divergent plate margins or accreting plate margins.
- It represents zone of divergence where there is continuous upwelling of molten material (lava) and thus new oceanic crust is continuously formed.
Destructive plate margins
- These are also called as consuming plate margins or convergent plate margins.
- Two plates move towards each other or two plates converge along a line and leading edge of one plate overrides the other plate.
- The overridden plate is sub ducted or thrust into the mantle and thus part of the crust (plate) is lost in the mantle.
Conservative plate margins
- These are also called as shear plate margins
- Two plates pass or slide past one another along a transform faults and thus crust is neither created nor destroyed.
Fig- Different types of plate margins
- Hess postulated the concept of plate tectonics in 1960, in support of continental drift.
- The continents and ocean move with the movement of these plates.
- The present shape and arrangement of continent and ocean basins could be attained because of continuous movement of different plates.
Plate tectonic theory is based on the evidences of sea floor spreading and palaeomagnetism.