What do you understand by the continental drift theory ? What are the evidences in its support ? (200 Words)
Ans: Continental Drift theory had been proposed by Alfred Wegner in 1912, it talked about distribution of continents and the oceans. According to Wegner all continents used to form a single land mass known as PANGAEA and there was a mega ocean called as PANTHALASSA.
However, around 200 million years ago Pangaea began to split into two large land masses called as Laurasia and Gondwanaland which subsequently broke into many smaller continents.
The theory is backed by the following evidences
- Jig Saw fit: The Africa and South America continents are almost a perfect fit at 1000 fathom line.
- Rocks Age: As per the radiometric dating Rocks on the two sides of above mentioned continents are of the same age.
- Tillite: It’s a sedimentary rock formed out of deposits of glaciers. The sediments in India have counter parts found in six different landmasses of Southern Hemisphere.
- Placer Deposits: Ghana have rich placer deposits of gold in spite of having no source rock there but in Brazil.
- Distribution of Fossils: Plants, animals and fossils have been found to be identical across continents like Africa, Madagascar, India etc.
Continental drift theory was a prominent theory for quite some time, however,
ocean floor mapping and similar studies post war period changed the view and people moved towards convectional theory and plate tectonic theory etc.
What arguments can be put forward to support the concept of Sea Floor Spreading as proposed by Hess ? How does it differ from Continental Drift theory? (200 Words)
Sea Floor Spreading is a process which explains the construction of new oceanic
crust at Mid oceanic ridge and destruction of old ones at trench. The phenomenon by Henry Hess can be supported by following arguments:
- Validated by latest plate tectonic movement theory.
- Formation of mid oceanic ridge on constructive boundary of plates.
- Age of soil on sea floor indicates a trend of decreasing pattern from trench to mid oceanic ridge implying new formation of sea floor by molten magmatic materials.
- Recent Geological studies and satellites have proved the continuous expansion of ocean crust near mid oceanic ridge.
- Proven phenomenon of paleo magnetism can also be taken as evidence for seafloor spreading.
Sea Floor Spreading differs from Continental drift theory as continental drift theory proposed by Wegener depends on Moon’s gravitational pull, Tides, rotational motion of Earth etc. to drift. It also fails to explain reason for volcanic eruption ,mountain building process and formation of islands.
whereas Seafloor spreading: Magmatic plumes which are formed below crust are
the main driving force. It is validated by plate tectonic theory. This phenomenon
correctly explains the spreading and formation of ocean crust along with mid ocean ridges and islands.
Though the Continental Drift theory have become obsolete but the main idea behind this phenomenon for formation of ocean floor and drift of continent was the driving force behind all other modern theories including sea floor spreading.