Wandering Continents by Carol Tresa of IX B

SEMINAR REVIEW

by Carol Tresa of Std. IX B

 

TOPIC: PLATE TECTONICS

Date: 7th July 2012

Resource Person: 
Mr.Unnikkrishnan Warrier
Scientist, CWRDM

WANDERING CONTINENTS

On July 07^th, Mr. Unnikrishnan Warrier, a scientist from CWRDM, conducted a class on Plate Tectonics. The class started with the Continental Drift Hypothesis of 1970 by Dr. Alfred Wegenar who was a German Climatologist and Geophysician. He wrote a book called “Origin of Continents and Oceans” in 1915 which by 1970 had evolved into a revolution in Geosciences called - ‘The Theory of Plate Tectonics’. 

 A Theory has evidence while a hypothesis is proved to only some extent. The class was about how a hypothesis became a Theory. The Hypothesis stated that about 200 million years ago, a super continent called PANGAEA, Latin for all Lands, started breaking and drifting to different positions. The ocean that was there was Panthalassa which named after the Greek God of the sea. The first sea that formed after the division was Tethys.

A great debate took place then. Wegenar said that there was similarity between the coastlines on opposite sides of the South Atlantic. But it was put down by the fact that shorelines were modified by erosion. Another point was that fossils of animals such as Mesosaurus, Lystrosaurus and Glossopteris were found in places that had so many kilometers of sea in between the land that these animals could not have travelled long distances. This was opposed by the fact that there were lots of sea channels through which animals could have migrated.

Wegenar believed that the centripetal force caused the continents to move away, but he was not able to answer why they did not move in the same direction as they should and also why the radius of the earth remained same even after a lot of shifting. Thus, it remained a hypothesis.

Some people continued to prove the hypothesis. They found that the Atlantic Ocean had a ridge in the middle of the ocean floor where there was a lot of volcanic activity. They found that the age of rock increased as they moved towards the coastlines from the ridge. They found that the seafloor spreaded out and named it sea floor spreading. But why it happened was not answered. Interior of the earth consists of crust, mantle, outer core and inner core. The density is different for all these layers. Continents have a composition – SIAL (Silica and Aluminium), while oceans have SIMA (Silica and Magnesium). When certain waves were passed through the interior of the earth, it was found that the upper mantle is like a paste and also elastic.Thus, there came the Lithosphere (crust and upper mantle) and Asthinosphere (lower mantle). It was also found that the earth was made up of different plates that consisted of both solid crust and ocean floor. Plates are divided as Major (Eurasian plate), and Minor (Arabian plate) and Micro (Madagascar) based on their size. In a major plate, there may be many minor and micro plates. Movement in a plate is the activity along the plate borders like:

1. Convergent or destructive boundary – the area where twp plates come close and collide, where crust is destroyed and islands form. Eg:  Pacific Ocean where there are lots of islands.

2. Divergent or constructive boundary – the area where two plates move apart and mid-ocean ridges form. This was misunderstood as ‘ocean floor spreading’. Eg: -  Atlantic Ocean where there are no islands.

3. Transform or conservative boundary – the area where two plates slide past in opposite directions to form transform faults. Eg: - San Andrea’s fault.

It was also found that equal amount of earth’s crust is destroyed and constructed, so the radius remains same. Plumes are the cyclic motions inside the earth that carry the plates. This is how the Himalayas were formed. They are young mountains. Indian plate was taken to the North North-East and collided with the Eurasian plate. The Tethys Sea was elevated and its sediments formed the Himalayas. Tethys was deeper in the North, so Himalayan Mountains are highest in the northern side. This can be proved because fossils of sea animals and limestone- which only forms in water- are found in the Himalayas. It is still building higher by 1cm/year. The plateau was formed due to an outbreak of the plume that carried the Indian plate. The Gangetic plains were formed due to weathering of sediments on the mountains. The Tethys sea water went South South-West to Pakistan. It is said that Tethys sea water flowed as the River Saraswati, but it is having lot of controversies. We saw how the continents have moved over different periods like Triassic period, Jurassic period and Cretaceous period.

Earthquake is a release of energy. The circum Pacific belt is prone to earthquakes. Tsunami is the after effect of a sub-marine earthquake. It is called ‘Harbour waves’ in Japan as it does not affect any ships that are sailing in mid-ocean. It affects ships in the harbours. Tsunami waves have ‘crust’ and ‘truff’. When a crust hits the coast first, there is huge increase in water level without notice. When a truff comes first, the sea will withdraw and hit back, a lot stronger. 

The factors to find out if two continents were together are geographical continuity, ethological continuity, structural continuity and chronological continuity. Earthquakes have compressional waves, i.e. primary waves that are a very big threat to buildings, and secondary waves. Buildings are sometimes placed on ‘concrete balls’. That is an engineering technique to prevent damages due to earthquakes. The requirements for emergencies are:

* Co-operation

* Proper civilian defense

* Mutual understanding

* Infrastructural development

* Practice

We must also have general knowledge as on what to do in time of an earthquake. We must be in an open space during an earthquake. We must also have everything like cupboards and clocks attached to the walls. We also learnt that local time is very important as its absence will cause less usage of man power.