Class 11 Geography (Fundamental Of Physical Geography) Chapter 2 The Origin And Evolution Of the Earth

Key Concept: Timeline Recall

b) 3,800 million years

[Solution Description] According to the modern scientific view, the evolution of life began around 3,800 million years ago.

Key Concept: Comparative Analysis

c) Otto Schmidt and Carl Weizascar

[Solution Description] The original Nebular Hypothesis was proposed by Immanuel Kant and later revised by Laplace. However, it was Otto Schmidt and Carl Weizascar who revised this hypothesis to include the concept of a solar nebula composed of hydrogen, helium, and dust, which played a crucial role in the formation of planets.

Key Concept: Density Gradient

b) Increases

[Solution Description] When moving from the Earth’s crust to the core, the density of materials increases. This increase in density is due to gravitational settling where denser materials, such as metal alloys, are located deeper within the Earth’s layers.

Key Concept: Cause and Effect

b) Subduction of one plate beneath another

[Solution Description] At convergent plate boundaries, tectonic plates move towards each other. The intense pressure from this movement causes one plate to be forced or subducted under another. This subduction process accumulates stress in the Earth’s crust. When the built-up energy is eventually released as seismic waves, it results in an earthquake.

Key Concept: Layer Identification

a) Crust, mantle, outer core, inner core

[Solution Description] From the surface towards the center, Earth’s layers are ordered as crust, mantle, outer core, and inner core. This differentiation is based on density.

Key Concept: Basic Formation

b) Cohesion

[Solution Description] The formation of planetesimals primarily occurs through cohesion and accretion, where small particles in space stick together to form larger bodies. Cohesion refers to the sticking together of similar particles, while accretion involves the gradual accumulation of additional material.

Key Concept: Evolution Stages

c) Differentiation

[Solution Description] The differentiation process led to the separation of materials inside the Earth based on density, forming a core, mantle, and crust. This resulted in the development of Earth’s layered structure.

Key Concept: Big Bang Timeline

c) 380,000 years after the Big Bang

[Solution Description] The cosmic microwave background radiation became observable approximately 380,000 years after the Big Bang. This event is significant because it marks the time when the universe cooled enough for electrons and protons to combine into neutral hydrogen atoms, allowing light to travel freely through space.

Key Concept: Density Differences

b) Regions of higher density contracted due to gravitational forces.

[Solution Description] Density differences in the early universe caused regions with slightly higher mass and gravitational attraction to contract under their own gravity. This led to the clumping of matter, forming proto-galaxies which eventually evolved into galaxies.

Key Concept: Temperature Drop

c) 4500 K

[Solution Description] Post-Big Bang, as the universe expanded, it cooled down. Atomic matter formed when the temperature dropped to about 4,500 K after approximately 300,000 years.

Key Concept: Simple Fact Recall

c) 4,100 million years ago

[Solution Description] Earth’s oceans formed within the first 500 million years of its formation. Earth is approximately 4,600 million years old, so the oceans formed around 4,100 million years ago.

Key Concept: Differentiation Process

b) Separation of materials based on density

[Solution Description] Differentiation is a process where materials separate based on their densities. The denser materials move towards the center, forming the core, while less dense materials form layers above, like the mantle and crust.

Key Concept: Formation Process

b) Accretion

[Solution Description]

The Revised Nebular Hypothesis suggests that planets formed through a process known as accretion. This involves small particles sticking together over time to form larger bodies, eventually leading to the formation of planets.

Key Concept: Layer Identification

d) Crust, Mantle, Outer Core, Inner Core

[Solution Description] The Earth’s internal structure is composed of four main layers: crust, mantle, outer core, and inner core. The order from the surface to the center is straightforward as it follows this composition sequence.

Key Concept: Light Year

b) $9.461 \times 10^{12}$ km

[Solution Description] A light year is defined as the distance light travels in one year. This distance is approximately $9.461 \times 10^{12}$ km.

Key Concept: Accretion Process

c) By accretion

[Solution Description] The transformation of planetesimals into larger bodies occurs through accretion, where smaller objects stick together over time due to gravitational forces.

Key Concept: Historical Context

c) 1796

[Solution Description] Pierre-Simon Laplace revised the Nebular Hypothesis in 1796, providing a model for the formation of the solar system.

Key Concept: Layer Identification

a) Crust

[Solution Description] The Earth’s layers vary in density. The crust, being the outermost layer, has a lower density compared to the other internal layers such as the mantle and core. Among the given options, the crust is identified as having the lowest density.

Key Concept: Geological Time Scale

b) Origin of life

[Solution Description]

The origin of life on Earth is estimated to have occurred around 3.5 billion years ago. This time period marks the appearance of the first simple organisms, such as bacteria and archaea, which are evidenced by fossil records.

Key Concept: Initial Earth Conditions

b) Barren, rocky, and hot object

[Solution Description] The Earth’s early condition was volatile due to high internal temperature and density.

Key Concept: Photosynthesis Impact

c) It increased oxygen levels.

[Solution Description]

Photosynthesis led to the oxygenation of both the oceans and the atmosphere. Initially, it resulted in an increase in oceanic oxygen levels until saturation was reached. Following this, oxygen began to accumulate in the atmosphere, significantly altering its composition by increasing atmospheric oxygen levels.

Key Concept: Basic Concepts

d) Oxygen

[Solution Description] Earth’s early atmosphere mainly consisted of hydrogen, helium, carbon dioxide, and water vapor. Oxygen was not present in significant amounts until much later due to photosynthesis by early life forms.

Key Concept: Basic Concept

d) The universe is expanding from a singular point.

[Solution Description] The Big Bang Theory suggests that the universe originated from an extremely hot and dense state and has been expanding over time. This theory implies that the universe is continually growing larger and more spread out, starting from a singular point.

Key Concept: Layered Structure

b) Differentiation

[Solution Description] Differentiation is the process that resulted in the formation of Earth’s layers. During differentiation, denser materials like iron sank to form the core, while lighter materials rose to form the mantle and crust.

Key Concept: Temperature Drop

c) 4,500 K

[Solution Description] The universe became transparent when its temperature dropped to 4,500 K. This process is known as recombination, where electrons could combine with protons to form neutral hydrogen atoms.

Key Concept: Chemical Evolution, Role of Photosynthesis

c) By oxidizing the atmosphere, enabling complex biochemical processes

[Solution Description] Photosynthesis was pivotal in altering the composition of Earth’s atmosphere by producing oxygen as a by-product, leading to oxidation reactions that enabled complexity in chemical evolution and paved the way for aerobic organisms.

Key Concept: Conceptual Application

a) Gravitational collapse

[Solution Description] The primary process leading to star formation from localized clumps of gas in a nebula is gravitational collapse. In this process, gravity pulls the gas together into denser regions. As these regions become denser, they heat up due to increased pressure and temperature, ultimately leading to nuclear fusion when conditions are right, forming a new star.

Key Concept: Basic Layers

b) Mantle

[Solution Description] The Earth’s layers from outermost to innermost are Crust, Mantle, Outer Core, and Inner Core. Directly above the Outer Core is the Mantle.

Key Concept: Basic Definition

a) Small rounded objects formed by cohesion

[Solution Description] Planetesimals are small rounded objects formed by the cohesion of smaller particles in a gas cloud during the planetary accretion process.

Key Concept: Basic Concept

b) 2,500-3,000 million years ago

[Solution Description] As per the syllabus, photosynthesis evolved between 2,500-3,000 million years ago, which contributed oxygen to Earth’s oceans and atmosphere.

Key Concept: Density Variation

b) Increases significantly

[Solution Description] As one moves from the Earth’s crust to its core, the density of the materials increases. This is because heavier elements such as iron are more prevalent at the core, whereas lighter elements are found in the crust.

Key Concept: Ocean Formation Process

c) Rainwater collecting in Earth’s depressions

[Solution Description] Oceans were formed when rainwater collected in depressions on Earth’s surface. This process occurred after carbon dioxide dissolved in rainwater, decreased temperature, and caused condensation.

Key Concept: Comparative Analysis

d) Focus on the solar nebula’s role in planet formation.

[Solution Description] The revision by Otto Schmidt and Carl Weizascar emphasized the role of the solar nebula, a rotating disk of gas and dust, in the formation of planets. This focuses on detailed processes within the nebula that were not highlighted in earlier versions.

Key Concept: Comparative Analysis

b) Solar winds

[Solution Description] The loss of the primordial atmosphere was primarily due to solar winds, which stripped away lighter elements like hydrogen and helium from the early Earth. In contrast, volcanic eruptions contributed significantly to the formation of the current atmosphere by releasing gases such as carbon dioxide, water vapor, nitrogen, etc., into the atmosphere.

Key Concept: Plate Boundaries

b) Convergent

[Solution Description] Subduction zones occur at convergent plate boundaries where one tectonic plate moves under another and sinks into the mantle. This process is characteristic of a convergent boundary.

Key Concept: Simple Definition

b) A measure of distance

[Solution Description] A light year is defined as the distance that light travels in one year. Since light travels at a speed of approximately $299,792,458 \, m/s$, it covers a vast distance over a year.

Key Concept: Process Understanding

b) Accretion

[Solution Description] According to the Nebular Hypothesis, a rotating cloud of gas and dust begins to collapse under gravity, forming a solar nebula. Within this nebula, small particles begin to collide and stick together due to electrostatic forces and gravitational attraction, forming larger bodies called planetesimals. This initial accumulation of material is known as accretion. Therefore, the primary process leading to the formation of planetesimals is accretion.

Key Concept: Formation Process

a) Small rounded objects formed by cohesion

[Solution Description] Planetesimals are small, rounded objects that form from the coalescence and cohesion of dust and gas in a protoplanetary disk. These bodies can come together under gravitational forces to form planets.

Key Concept: Simple Processes

c) Degassing

[Solution Description] Degassing refers to the release of gases from the Earth’s interior through volcanic eruptions or other geological processes. This contributed significantly to the formation of the early atmosphere.

Key Concept: Evidence Analysis

c) Identical fossils found on different continents

[Solution Description] Alfred Wegener used various types of evidence to support his Continental Drift Theory. One of the key pieces of evidence was fossil records. Fossils of the same species were found on continents that are currently separated by oceans, suggesting these continents were once connected.

Key Concept: Theory Comparison

b) Steady-State Theory

[Solution Description] The Steady-State Theory proposes the continuous creation of matter to maintain a constant density throughout the universe despite its expansion.

Key Concept: Process Sequence

b) Nebula formation, development of clumps, star formation

[Solution Description] The process starts with the accumulation of hydrogen gas in a large cloud called a nebula. Within this nebula, localized clumps form and grow into denser gaseous bodies. These dense clumps eventually lead to star formation. Therefore, the correct sequence is: Nebula formation, development of clumps, and then star formation.

Key Concept: Impact of Solar Winds

c) Stripped off hydrogen and helium

[Solution Description] The early Earth’s atmosphere was composed mainly of hydrogen and helium. Solar winds, being streams of charged particles from the sun, had the energy to strip away these lighter gases. Thus, the effect of solar winds led to the removal of hydrogen and helium, leaving behind a denser atmosphere consisting of heavier gases such as nitrogen and carbon dioxide.

Key Concept: Concept Identification

d) Gravitational force

[Solution Description] Gravitational force is the main driving factor that leads to the collection and condensation of materials, resulting in the formation of a core within a gas cloud.

Key Concept: Evolution Stages

c) Third stage

[Solution Description] Photosynthesis began significantly modifying Earth’s atmosphere during the third stage of its evolution. This process introduced oxygen into the atmosphere, leading to substantial changes in atmospheric composition.

Key Concept: Nebular Hypothesis

d) Edwin Hubble

[Solution Description] The Nebular Hypothesis, initially proposed by Kant and Laplace, was revised by Schmidt and Weizascar. Therefore, none of these options except for Carl Weizascar were not involved in its revision.