Class 11 Geography (Fundamental of Physical Geography) Chapter 4 Distribution of Oceans and Continents

Key Concept: Historical Figures

d) Alfred Wegener

[Solution Description]

Alfred Wegener is credited with first proposing the theory of continental drift in 1912, suggesting that continents were once joined together and have since drifted apart.

Key Concept: Plate Tectonics Theory

b) Plate Tectonics

[Solution Description] The theory that explains the movement of Earth’s lithosphere over the asthenosphere is the Plate Tectonics theory. It describes how the lithospheric plates float on the semi-fluid asthenosphere beneath them.

Key Concept: Time Scale Effectiveness

d) Millions of years

[Solution Description]

Wegener believed that the pole-fleeing and tidal forces would be effective over a time scale of millions of years, allowing for gradual movement of continents.

Key Concept: Basic Concept

c) Formation of new oceanic crust as lava emerges at mid-oceanic ridges.

[Solution Description] Sea floor spreading involves the rupture of oceanic crust and the formation of new crust from lava that emerges at mid-oceanic ridges.

Key Concept: Basic Terms

c) Mid-oceanic ridge

[Solution Description] The components of continental margins include the continental shelf, continental slope, continental rise, and deep-oceanic trenches. Each plays a role in the transition from land to ocean floor. The mid-oceanic ridge is not a part of the continental margins; it is located at divergent plate boundaries.

Key Concept: Basic Concept

c) Similar ages and composition

[Solution Description] Rocks that are equidistant from mid-oceanic ridges share similarities in their age and composition due to the symmetrical spreading of the ocean floor. The magma that creates these rocks spreads out evenly on both sides of mid-oceanic ridges, leading to similar characteristics.

Key Concept: Basic Concept

d) Alfred Wegener

[Solution Description] The theory of continental drift was proposed by Alfred Wegener in 1912, suggesting that continents were once joined and have since drifted apart.

Key Concept: Process Understanding

b) Sea floor spreading

[Solution Description] At divergent boundaries, sea floor spreading is the primary process that leads to the formation of new oceanic crust. As tectonic plates move apart, magma rises from the mantle to fill the gap, solidifying to create new crust.

Key Concept: Convergence Types

b) Oceanic-continental

[Solution Description] An oceanic-continental convergent boundary occurs when an oceanic plate collides with a continental plate. In this interaction, the denser oceanic plate is forced under the lighter continental plate.

Key Concept: Basic Features

b) Central rift system

[Solution Description] Mid-oceanic ridges are known for their central rift system, which is a key feature at the crest of these underwater mountain chains.

Key Concept: Sea Floor Spreading

b) The symmetry in magnetic properties on both sides of mid-ocean ridges

[Solution Description] Sea floor spreading is evidenced by symmetric patterns of magnetic stripes on either side of a mid-ocean ridge, indicating periods of geomagnetic reversals. The orientation and age of these magnetic patterns match as they move away from the ridge, supporting the idea that new crust forms and spreads outward.

Key Concept: Basic Concept Understanding

c) Due to intense volcanic activity

[Solution Description] The Pacific Rim is called the “rim of fire” because of the high number of active volcanoes in the region, which are caused by tectonic plate boundaries and subduction zones along the rim.

Key Concept: Basic Definition

c) Both continental and oceanic lithosphere

[Solution Description]

Tectonic plates are massive slabs that make up Earth’s surface, consisting mainly of two types of lithosphere: continental and oceanic. The lithosphere is the rigid outer layer of Earth. Therefore, tectonic plates are composed of both continental and oceanic lithosphere.

Key Concept: Basic Definition

d) All Sea

[Solution Description] The term ‘Panthalassa’ comes from Greek words where ‘pan’ means all and ‘thalassa’ means sea, indicating it is a “universal or global sea.”

Key Concept: Basic Concept

b) Mid-oceanic ridges

[Solution Description] The process of seafloor spreading involves volcanic activity primarily at mid-oceanic ridges. These ridges are underwater mountain ranges where new oceanic crust forms through volcanic eruptions, pushing older crust away.

Key Concept: Evidence of Drift

b) Distribution of identical species

[Solution Description] Evidence supporting the theory of continental drift includes matching coastlines, fossil correlations, geological formations, and climatic indicators. Among the options, “Distribution of identical species” directly ties into the concept of identical species’ fossils found on different continents, which bolsters the argument for continental drift.

Key Concept: Historical Figures

c) Abraham Ortelius

[Solution Description] Abraham Ortelius was among the earliest to suggest that continents might have been joined and later separated.

Key Concept: Transform Faults

b) Mid-oceanic ridges

[Solution Description]

Transform faults are fractures along which two tectonic plates slide past each other. They are frequently found perpendicular to mid-oceanic ridges, accommodating the differential motion between segments of diverging plates.

Key Concept: Volcanic Activity

d) Mid-oceanic ridges

[Solution Description] Volcanic eruptions are most commonly observed along mid-oceanic ridges. These ridges are underwater mountain ranges formed by plate tectonics where magma rises from beneath the Earth’s crust, leading to frequent volcanic activity.

Key Concept: Ocean Floor Features

b) Volcanic eruptions

[Solution Description] Mid-ocean ridges are characterized by volcanic activity. Volcanism occurs because tectonic plates are moving apart, allowing magma to rise from beneath the Earth’s crust.

Key Concept: Plate Movement Forces

c) Convection cells

[Solution Description] Convection cells or convective flow in the Earth’s mantle are responsible for the movement of tectonic plates, involving the circular movement of heated material rising, spreading, cooling, and sinking.

Key Concept: Basic Concept

d) Volcanic eruptions and lava flow

[Solution Description] New oceanic crust forms at mid-oceanic ridges due to volcanic eruptions and lava flow. As magma rises through the Earth’s mantle at these ridges, it cools and solidifies to form new crust.

Key Concept: Basic Concept

c) Mid-oceanic ridges

[Solution Description] Volcanic eruptions at mid-oceanic ridges bring lava to the surface, forming new oceanic crust.

Key Concept: Rate of Movement

b) Magnetic field stripes

[Solution Description] Scientists use strips of normal and reverse magnetic fields, which are parallel to mid-oceanic ridges, to calculate the rates of plate movement.

Key Concept: Historical Plate Movement

b) 200 million years

[Solution Description] India began its northward movement about 200 million years ago, drifting from the ancient supercontinent Gondwana.

Key Concept: Plate Identification

d) Pacific Plate

[Solution Description] The Pacific Plate is one of the largest and most significant tectonic plates on Earth, covering a vast area in the Pacific Ocean.

Key Concept: Types of Plate Boundaries

a) Divergent

[Solution Description]

The type of plate boundary where the tectonic plates move away from each other is known as a divergent boundary. This occurs when two tectonic plates separate and create new crust as magma rises to the surface.

Key Concept: Basic Concept

a) Mid-oceanic ridges

[Solution Description] The formation of new oceanic crust occurs at mid-oceanic ridges. Volcanic eruptions bring new lava to the surface, which solidifies and forms new crust as it cools.

Key Concept: Matching Coastlines

b) Continental Drift

[Solution Description] The matching coastlines of Africa and South America suggest that these continents were once joined together as part of a larger landmass. This observation supports the theory of continental drift, proposed by Alfred Wegener, which states that continents have moved over geologic time to their current locations.

Key Concept: Source of Heat

c) Radioactive decay

[Solution Description] One of the primary sources of heat within the Earth that drives plate movement is radioactive decay. Radioactive elements such as uranium, thorium, and potassium undergo decay, releasing heat that helps maintain the temperature of the Earth’s interior.

Key Concept: Evidence Identification

b) Tillite

[Solution Description] Tillite is a sedimentary rock formed from glacial deposits. Its presence in various continents serves as evidence of past glacial activity and supports the theory of continental drift by showing that these regions were once connected.

Key Concept: Basic Definition

b) Rich deposits of minerals found in river beds

[Solution Description] Placer deposits are accumulations of valuable minerals formed by gravity separation during sedimentary processes. They typically occur in riverbeds or beaches where water action concentrates heavy, resistant minerals like gold, zircon, and platinum.

Key Concept: Matching Continents

c) Africa and South America

[Solution Description] The coastlines of Africa and South America are noted for their remarkable jig-saw-fit appearance, which is often used as evidence for the theory of continental drift.

Key Concept: Abyssal Plains

c) Between continental margins and mid-oceanic ridges

[Solution Description] Abyssal plains are flat areas located between the continental margins and the mid-oceanic ridges. They are known for their smooth topography and thin sediment layers.

Key Concept: Plate Tectonics

b) The plates slide past one another without creating or destroying crust.

[Solution Description] At transform plate boundaries, tectonic plates slide past each other horizontally. This kind of boundary is characterized by lateral motion, which can cause earthquakes due to the friction and pressure build-up between the sliding plates.

Key Concept: Minor Plate

d) Antarctica

[Solution Description] Antarctica is a major tectonic plate, whereas Nazca, Arabia, and Philippines are classified as minor plates.

Key Concept: Ocean Floor Characteristics

c) 200 million years

[Solution Description] The oldest rocks found in the oceanic crust are approximately 200 million years old. This information comes from dating techniques used on samples collected from the ocean floor.

Key Concept: Evidence Recognition

d) Matching coastlines

[Solution Description] One of the key pieces of evidence for continental drift is the matching coastlines of continents, particularly how the east coast of South America fits closely with the west coast of Africa.

Key Concept: Theory Comparison

c) It involves mantle convection

[Solution Description] Arthur Holmes proposed that mantle convection currents are responsible for the movement of continents. This differs from Wegener’s original idea, which suggested pole-fleeing force and tidal forces as mechanisms. Holmes’ theory provided a more plausible scientific explanation involving heat-driven movements within the Earth’s mantle.

Key Concept: Basic Definition

b) Extensive flat areas between continental margins and mid-oceanic ridges

[Solution Description] Abyssal plains are vast, flat regions located between continental margins and mid-oceanic ridges in the deep ocean floor.

Key Concept: Basic Concepts

b) Mid-oceanic ridges

[Solution Description] The mid-oceanic ridges are known for their symmetrical patterns of rock age and composition due to sea floor spreading.

Key Concept: Radioactive Elements

d) They produce thermal differences in the mantle

[Solution Description] Radioactive elements generate heat through their decay, which causes thermal differences within the mantle. This heat results in the formation of convection currents that facilitate the movement of tectonic plates according to Holmes’ theory.

Key Concept: Basic Concept

b) They are relatively young

[Solution Description] Thin sediment deposits indicate that the ocean floor is relatively young. This is because if the ocean floor were older, there would be more time for sediments to accumulate.

Key Concept: Real-World Implications, Geological Processes

c) Rising height of the Himalayas

[Solution Description] The northward movement of the Indian plate has several implications, one being the continued uplift of the Himalayan mountain range due to the collision with the Eurasian plate. This process impacts global climate patterns as the Himalayas play a crucial role in influencing monsoons and weather systems across Asia. The correct answer involves understanding these geophysical dynamics.

Key Concept: Rate Identification

a) 1 cm/year

[Solution Description] The Arctic Ridge has a very slow rate of plate movement in comparison to other locations such as the East Pacific Rise. From the syllabus, it is stated that the rate of plate movement at the Arctic Ridge is less than 2.5 cm/year.

Key Concept: Plate Location

d) Between the Philippine and Indian plate

[Solution Description] The Caroline plate is located between the Philippine and Indian plate, north of New Guinea.

Key Concept: Plate Tectonics Basics

c) Both continental and oceanic lithosphere

[Solution Description]

A tectonic plate is made up of both continental and oceanic lithosphere. The lithosphere is the rigid outer layer of Earth, which includes the crust and part of the upper mantle. Plates can carry continents, oceans, or both.

Key Concept: Geological Features

b) Mid-ocean ridge

[Solution Description] Divergent boundaries are characterized by tectonic plates moving apart, leading to the formation of new crust. One prominent feature formed here is the mid-ocean ridge, which is a continuous mountain range beneath the ocean.

Key Concept: Plate Boundary Dynamics

b) Oceanic trench

[Solution Description] At a convergent boundary, one tectonic plate is often forced below another in a process called subduction. This results in the formation of oceanic trenches or mountain ranges depending on whether the plates involved are oceanic or continental. When an oceanic plate converges with a continental plate, the denser oceanic plate subducts beneath the lighter continental plate, forming a trench. If two continental plates collide, they can create large mountain ranges.

Key Concept: Comparative Analysis

c) Formed from glacial deposits

[Solution Description] Tillite is unique among sedimentary rocks because it forms specifically from glacial deposits. Other sedimentary rocks might form from different processes such as erosion, precipitation, or volcanic activity. The key characteristic that sets tillite apart is its origin from compacted and lithified glacial material.

Key Concept: Historical Figures

b) Antonio Pellegrini

[Solution Description] Antonio Pellegrini was the first to create such a map illustrating the possibility of continents being joined, which laid foundational groundwork for later theories on continental drift.

Key Concept: First Proposer

c) Abraham Ortelius

[Solution Description] Abraham Ortelius, a Dutch map maker, was the first person to propose the idea that continents might have moved in 1596.