Distribution of Oceans and Continents


1. Multiple choice questions.

(i) Who amongst the following was the first to consider the possibility of Europe, Africa and America having been located side by side.

(a) Alfred Wegener             (c) Abraham Ortelius

(b) Antonio Pellegrini        (d) Edmond Hess

Answer: (c) Abraham Ortelius. 

(ii) Polar fleeing force relates to:

(a) Revolution of the Earth         (c) Rotation of the earth

(b) Gravitation                             (d) Tides

Answer: (c) Rotation of the Earth.

(iii) Which one of the following is not a minor plate?

(a) Nazca         (c) Philippines

(b) Arabia       (d) Antarctica

Answer: (d) Antarctica.

(iv) Which one of the following facts was not considered by those while

discussing the concept of sea floor spreading?

(a) Volcanic activity along the mid-oceanic ridges.

(b) Stripes of normal and reverse magnetic field observed in rocks of ocean

floor.

(c) Distribution of fossils in different continents.

(d) Age of rocks from the ocean floor.

Answer: (c) Distribution of fossils in different continents.


 (v) Which one of the following is the type of plate boundary of the Indian plate along the Himalayan mountains?

(a) Ocean-continent convergence

(b) Divergent boundary

(c) Transform boundary

(d) Continent-continent convergence

Answer: (d) Continent-continent convergence.


2. Answer the following questions in about 30 words.

(i) What were the forces suggested by Wegener for the movement of the continents?

Answer: Wegener proposed two forces for continental drift:

1. Polar Fleeing Force: Earth's rotation supposedly flung continents outwards, especially towards the equator.

2. Tidal Force: Gravitational pull from the moon and sun tugged on continents, contributing to movement.

    While their role is debated, these ideas paved the way for understanding plate tectonics.

(ii) How are the convectional currents in the mantle initiated and maintained?

Answer: Earth's internal heat and radioactive decay set up temperature differences in the mantle. Hot parts rise, cooler parts sink, creating a giant, looping circulation like boiling soup. This continuous movement keeps the convectional currents going!


(iii) What is the major difference between the transform boundary and the convergent or divergent boundaries of plates?

Answer: The key difference lies in crust creation/destruction:

*Transform: Plates slide past each other, no crust created or destroyed. Imagine two cars brushing sides as they pass.

*Convergent: Plates collide, crust crumple/subducts, mountains form. Think crumpling paper.

*Divergent: Plates pull apart, new crust forms in the gap, like a zipper unzipping.

    So, transform boundaries are all about sideways movement, while the others deal with adding or removing crust.


(iv) What was the location of the Indian landmass during the formation of the Deccan Traps?

Answer: Imagine a fiery dance: during the Deccan Traps' formation, roughly 60 million years ago, the Indian landmass wasn't in its cozy spot it occupies today. It was much further south, nestled near Antarctica and Madagascar, basking in the southern tropics. This fiery period shaped the landscape we know now, leaving behind the vast basalt plateau of the Deccan Traps.


3. Answer the following questions in about 150 words.

(i) What are the evidences in support of the continental drift theory?

Answer: Several compelling lines of evidence support the continental drift theory, now known as plate tectonics:

1. The Jigsaw Puzzle Fit: The coastlines of South America and Africa appear remarkably like interlocking pieces when aligned, suggesting they were once joined.

2. Fossil Kinship: Similar fossils of land-dwelling plants and animals are found on now-separated continents, indicating they shared a common landmass in the past.

3. Rock Matches: Matching rock formations and age of rocks across continents, like ancient mountain ranges on different sides of the Atlantic, point to a shared geologic history.

4. Magnetic Stripes: Symmetrical strips of alternating magnetic polarity on the ocean floor mirror the Earth's magnetic field reversals, supporting seafloor spreading and continental movement.

5. Continental Drilling: Deep-sea drilling reveals younger rocks closer to mid-ocean ridges and older rocks farther away, confirming seafloor spreading as the mechanism for continental movement.

    These diverse lines of evidence, from geology to paleontology and geophysics, paint a compelling picture of continents once forming a larger landmass and then drifting apart over millions of years.


(ii) Bring about the basic difference between the drift theory and Plate tectonics.

Answer: While both continental drift and plate tectonics explain the movement of continents, they differ in key ways:

Continental Drift (proposed by Alfred Wegener):

*Mechanism: Relied on forces like polar fleeing force and tidal drag to move continents.

*Lacked explanation: Didn't provide a convincing explanation for how forces could move massive continents.

*Seafloor spreading ignored: Didn't incorporate observations of seafloor spreading and magnetic stripes.

Plate Tectonics (modern understanding):

*Mechanism: Driven by mantle convection currents, moving plates horizontally over a liquid asthenosphere.

*Scientifically robust: Explains diverse geological phenomena like earthquakes, mountain building, and volcanic activity.

*Seafloor spreading integrated: Explains spreading ocean floors and movement of continents based on plate interactions.

In essence:

*Drift: More like pushing continents around.

*Plate tectonics: A complex, dynamic system of interacting plates driven by internal forces.

    Plate tectonics provides a deeper, more comprehensive understanding of Earth's dynamic surface and the forces that shape our planet.


(iii) What were the major post-drift discoveries that rejuvenated the interest of scientists in the study of distribution of oceans and continents?

Answer: The continental drift theory faced skepticism when initially proposed, and interest in continental distribution waned. However, several post-war discoveries revived scientific enthusiasm:

1. Mapping the Ocean Floor: Technological advancements allowed detailed mapping of the ocean floor, revealing:

*Mid-oceanic ridges: Long underwater mountain ranges with active volcanic eruptions, suggesting new crust formation.

*Seafloor spreading: Symmetrical patterns of magnetic stripes on either side of mid-ocean ridges, indicating seafloor spreading and continental movement.

2. Ocean Crust Age Dating: Studies showed rocks closer to mid-ocean ridges were younger than those farther away, confirming seafloor spreading and movement away from the ridges.

3. Deep-Sea Drilling: Projects like the Deep Sea Drilling Program retrieved rock samples from the ocean floor, further confirming seafloor spreading and providing valuable data on past environments and climates.

4. Plate Tectonics: These discoveries led to the development of plate tectonics, a comprehensive theory explaining continental movement, earthquakes, mountain building, and other geological phenomena. This renewed interest in the dynamic interactions between continents and oceans.

    These post-drift discoveries revolutionized our understanding of Earth's history and processes, fueling continued research and exploration of our planet's dynamic surface.


Answer Type By: Himashree Bora.