Question 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

(ii) Polar fleeing force relates to:

(a) Revolution of the Earth
(c) Rotation of the earth
(b) Gravitation
(d) Tides

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

(a) Nazca
(c) Philippines
(b) Arabia
(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.

(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

Accepted Answer

1.(i) (c) Abraham Ortelius was the first to consider the possibility of Europe, Africa and America having been located side by side.

(ii) (a) Polar fleeing force relates to the Revolution of the Earth.

(iii) (d) Antarctica is not a minor plate; it is a major tectonic plate.

(iv) (c) Distribution of fossils in different continents was not considered while discussing the concept of sea floor spreading.

(v) (d) The type of plate boundary of the Indian plate along the Himalayan mountains is Continent-continent convergence. — 1.(i) Abraham Ortelius in the 16th century first suggested that continents might have been joined together. Alfred Wegener later developed the continental drift theory.

(ii) Polar fleeing force is related to the centrifugal force due to Earth's revolution around the Sun.

(iii) Antarctica is a major plate, unlike Nazca, Arabia, and Philippines which are minor plates.

(iv) Sea floor spreading discussions focused on volcanic activity, magnetic stripes, and age of ocean floor rocks, but not on fossil distribution.

(v) The Indian plate collides with the Eurasian plate forming the Himalayas, a continent-continent convergent boundary.

Question 2

Answer the following questions in about 30 words.

(i) What were the forces suggested by Wegener for the movement of the continents?
(ii) How are the convectional currents in the mantle initiated and maintained?
(iii) What is the major difference between the transform boundary and the convergent or divergent boundaries of plates?
(iv) What was the location of the Indian landmass during the formation of the Deccan Traps?

Accepted Answer

(i) Wegener suggested that the continents moved due to forces like the polar fleeing force and tidal force.

(ii) Convectional currents in the mantle are initiated by heat from the Earth's core causing mantle material to rise and fall, maintaining the currents.

(iii) Transform boundaries involve plates sliding past each other horizontally, unlike convergent or divergent boundaries where plates collide or move apart.

(iv) During the formation of the Deccan Traps, the Indian landmass was located in the southern hemisphere near the equator, moving northwards. — (i) Wegener proposed forces such as polar fleeing force (centrifugal force due to Earth's rotation) and tidal force from the Moon and Sun to explain continental movement.

(ii) Heat from the Earth's core causes mantle material to heat up, become less dense and rise; upon cooling, it sinks, creating convection currents.

(iii) Transform boundaries are characterized by lateral sliding of plates, causing earthquakes but no creation or destruction of crust, unlike convergent (collision) or divergent (separation) boundaries.

(iv) Geological evidence shows the Indian plate was in the southern hemisphere during the Deccan Traps volcanic activity about 65 million years ago.

Question 3

Answer the following questions in about 150 words.

(i) What are the evidences in support of the continental drift theory?
(ii) Bring about the basic difference between the drift theory and Plate tectonics.
(iii) What were the major post-drift discoveries that rejuvenated the interest of scientists in the study of distribution of oceans and continents?

Accepted Answer

(i) Evidences supporting continental drift theory include the fit of the continents like South America and Africa, similarity of fossils across continents, matching geological formations, and paleoclimatic evidence such as glacial deposits in now tropical regions.

(ii) The drift theory proposed by Wegener suggested continents moved but lacked a mechanism. Plate tectonics explains the movement of lithospheric plates driven by mantle convection, providing a mechanism for continental drift and sea-floor spreading.

(iii) Major post-drift discoveries include the mapping of mid-ocean ridges, discovery of sea-floor spreading, paleomagnetic studies showing magnetic striping on ocean floors, and understanding of plate boundaries, which revived interest in continental and oceanic distribution. — (i) The matching coastlines, fossil records (like Mesosaurus), geological similarities, and evidence of past climates support the idea that continents were once joined.

(ii) Drift theory lacked explanation for forces causing movement; plate tectonics introduced mantle convection and plate boundaries as mechanisms.

(iii) Discoveries such as mid-ocean ridges, magnetic anomalies, and sea-floor spreading provided concrete evidence for plate movements and ocean basin evolution.

Question 4

Project Work

Prepare a collage related to damages caused by an earthquake.

Accepted Answer

This is a creative project work requiring students to collect images, news clippings, and information about earthquake damages and prepare a collage showcasing the impact of earthquakes on life and property. — The project helps students understand the destructive nature of earthquakes and raises awareness about earthquake preparedness and safety measures.

Question 5

What percentage of the Earth's surface is covered by continents, and what percentage is covered by oceanic waters?

Accepted Answer

29% continents and 71% oceanic waters — Continents cover approximately 29% of the Earth's surface, while the remaining 71% is covered by oceanic waters. This distribution is a fundamental fact in physical geography and helps understand the Earth's surface composition.

Question 6

Who first proposed the idea that the continents were once joined together, and in which year?

Accepted Answer

Abraham Ortelius, 1596 — Abraham Ortelius, a Dutch map maker, first proposed the possibility that continents were once joined together in 1596. Although Alfred Wegener later developed the comprehensive continental drift theory in 1912, Ortelius was the earliest to suggest this idea.

Question 7

According to Alfred Wegener's continental drift theory, what was the name of the super continent and the surrounding mega ocean?

Accepted Answer

Pangaea and Panthalassa — Wegener proposed that all continents were once joined as a single super continent called Pangaea, surrounded by a mega ocean named Panthalassa. This concept is central to the continental drift theory.

Question 8

Which two large continental masses did Pangaea split into according to Wegener's theory?

Accepted Answer

Laurasia and Gondwanaland — Pangaea first broke into two large continental masses: Laurasia in the north and Gondwanaland in the south. These subsequently fragmented into the continents we know today.

Question 9

What is the term used to describe the remarkable fit of the shorelines of continents such as Africa and South America, supporting continental drift theory?

Accepted Answer

Jig-Saw-Fit / jigsaw fit — The 'Jig-Saw-Fit' refers to the matching coastlines of continents like Africa and South America, which fit together like pieces of a puzzle. This evidence supports the idea that these continents were once joined.

Question 10

Which type of rock, formed from glacier deposits, provides evidence of similar ancient climates across southern continents and supports continental drift?

Accepted Answer

Tillite — Tillite is a sedimentary rock formed from glacial deposits. Its presence in Gondwana sediments across India, Africa, Antarctica, and other southern continents provides evidence of past glaciation and continental drift.

Question 11

Why are placer deposits of gold found on the Ghana coast significant evidence for continental drift?

Accepted Answer

Placer deposits are accumulations of valuable minerals like gold. The gold deposits on the Ghana coast are significant because there are no source rocks in the region, and the gold is believed to have originated from Brazil when the two continents were joined. This supports the idea that Africa and South America were once connected. — Placer deposits of gold on the Ghana coast, without local source rocks, indicate that the gold originated from Brazil. This suggests that the two continents were once adjacent, providing strong evidence for continental drift.

Question 12

Which fossil reptile's skeletons found only in Southern Cape province of South Africa and Brazil provide evidence for continental drift?

Accepted Answer

Mesosaurus — Mesosaurus was a small reptile adapted to shallow brackish water. Its fossils found only in South Africa and Brazil support the idea that these continents were once joined.

Question 13

Which two forces did Wegener suggest as responsible for the drifting of continents?

Accepted Answer

Polar-fleeing force and tidal force — Wegener proposed that the polar-fleeing force (due to Earth's rotation and equatorial bulge) and tidal force (due to moon and sun's attraction) caused continental drift, although these forces were later considered inadequate.

Question 14

What is the main idea behind Arthur Holmes' convectional current theory related to continental drift?

Accepted Answer

Arthur Holmes proposed that convection currents in the Earth's mantle, caused by radioactive decay heating, generate circular movements of molten rock. These currents can move the lithospheric plates, providing a force that drives continental drift. — Holmes suggested that thermal differences in the mantle due to radioactive elements cause convection currents. These currents move the mantle material in circular patterns, which can push and pull the overlying plates, explaining continental movement.

Question 15

Describe the three major divisions of the ocean floor based on depth and relief forms.

Accepted Answer

The ocean floor is divided into three major divisions: (1) Continental Margins, which include the continental shelf, slope, rise, and deep-ocean trenches; (2) Deep-sea Basins or Abyssal Plains, which are flat areas between the continental margins and mid-ocean ridges where sediments accumulate; and (3) Mid-Oceanic Ridges, which are long mountain chains with central rift valleys and volcanic activity. — Ocean floor configuration includes continental margins as transition zones, abyssal plains as flat sedimented areas, and mid-oceanic ridges as underwater mountain chains with active volcanism, all important for understanding ocean and continent distribution.

III CLIMATE AND VEGETATION

III CLIMATE AND VEGETATION — Study Notes

Introduction

Factors Influencing Climate

Climatic Regions of India

Practice Questions — III CLIMATE AND VEGETATION

All 6 Chapters in India - Physical Environment