DISTRIBUTION OF OCEANS AND CONTINENTS BY-AKANKSHA SONI
INTRODUCTION Oceans and continents will not continue to enjoy their present position in times to come. HOW? CONTINENTAL DRIFT THEORY Proposed by Alfred Wegner/ Wegner theory According to him, all continents formed a single mass called as PANGEA sorrounded by ocean called PANTHALASSA Some 200 million years ago, continent broke in 2 large landmass, LAURASIA and GONDWANALAND (North & south). Subsequently, they broke into further pieces forming smaller continents Reason of split- 1)Tidal force of moon (gravitation in west direction) 2) Difference between centre of gravity of continents and centre of rotation (thrust)
EVIDENCE Jig saw fit of continents- Eg. Africa and South American shorelines Fossil distribution Rocks of same age across oceans Placer deposits PLATETECTONICTHEORY It is a comprehensive, unified theory. It explains 1) Formation and destruction of plates, Movements, Distribution & magnitude of earthquakes, volcanoes, mountains etc PLATE- Lithosphere of earth consist of crust and upper mantle floating above asthenosphere. They are rigid and hard in nature.
Plates are divided into 1) MAJOR 2)MINOR MOVEMENT OF PLATES: North Ameritan Plote Eurasian Plate Juan de Fyca P 1)Thermal convective currents that Padific Platerise verticallv from mantle. The Plate /Indian form due to radioactive decav. Plate Padific Plate Plate African Plate Nazca Plate South American 2)Magma plumes- Long convective currents formed at core- mantle boundarv. They are not uniform and scattered Plate Seotia Antardtic Plate duu
TYPES OF PLATES: 1) Convergent (destructive) 2) Divergent(constructive) 3) Transform(Conservative) 1) CONVERGENT- Movement is face to face. Margins going downward gets melted and hence they are destructive. The location of subduction is Subduction zone C emme Convergence can occur in -1) continent- continent 2) Continent- ocean 3) ocean-ocean
DIVERGENT a al other. These sites known as spreading sites. Eg. Mid Atdlantic ridges (seafloor spreading). 3) TRANSFORM Crust is neither generated nor destroyed as plates slide past each other. between two theories, Plate tectonic has been proved as more real due to the nature of variable ich were not considered during Wegner's time. earth and it's movements
DISTRIBUTION OF PLATES Earthquakes and volcanoes are formed according to these boundaries. (intensity varies) 180 NORTH AMERICAN PLATE EURASIAN PLATE 60 Ridge EURASIAN PLATE Aleutian JUAN DE FUCA Trench PLATE Pacific ring of fire- Due to Esst active volcanoes in area Rise AFRICAN PLATE PACIFIC PLATE PLATE Jeva Trench UTH AMERICAN NAZCA PLATE PLATE INDO-AUSTRALIAN PLATE SCOTA 60 Boundary 0 2000 6000 Km Convergent Boundary Transform Boundary -A 180 ANTARCTIC PLATE 90 Figure 4.5: Major and minor plates of the world
MOVEMENT OF INDIAN PLATE e Form of continent- continent convergence * Journey started some 200 million years ago.The Tethys sea separated the continents. It collided Asia some 40 million vears ago It caused rapid uplift of Himalayas . An event occurred during journev-Lava outpoured in Deccan || 38 million traps EURASIAN PLATE INDIA TODAY years ago years ago tor It occurred before the formation of Himalavas 55 million years ago , INDIAN OCEAN Believed to be still continuing 71 million years ago EARLY INDIA