Test: The Origin And Evolution Of The Earth - UPSC MCQ

The correct answer is Option B. According to the text, life on Earth started around 3.8 billion years ago with blue algae, the earliest known life forms, which emerged from chemical reactions capable of replication. This aligns with the description that life evolved from chemical processes that produced molecules capable of forming living organisms. Options A, C, and D are incorrect because they either misstate the origin of life as plants or misinterpret the role of the Big Bang Theory and the composition of Earth's early atmosphere, which was initially devoid of oxygen until the advent of photosynthesis by life forms like blue algae.

- Assertion (A) is correct because the Nebular Hypothesis indeed describes the formation of planets from a rotating cloud of gas and dust surrounding a young sun.

- Reason (R) is also correct as it accurately describes the accretion process that leads to the formation of larger bodies from smaller particles.

- The reason is the correct explanation of the assertion, as it explains how the processes described in the Nebular Hypothesis occur.

The correct sequence of events based on the provided text about Earth's formation is as follows:

Step 4: As the Earth's internal temperature increased, materials inside began to differentiate based on their densities.
Step 2: Heavier materials, such as iron, sank towards the center due to their higher density, while lighter materials moved towards the surface.
Step 1: Subsequently, the Earth cooled, solidified, and condensed into a smaller size, and the cooling process led to the formation of the crust.
Step 3: During the formation of the moon, a giant impact further heated the Earth. Through the process of differentiation, the Earth-forming materials separated into different layers. These layers, from the surface to the center, include the crust, mantle, outer core, and inner core. The density of the materials increases from the crust to the core.

- Assertion (A) is correct; the layers of the Earth formed through differentiation, where heavier materials sank to the core while lighter materials rose to form the crust.

- Reason (R) is false because the early Earth was not just solid rock; it experienced significant internal heating, which played a crucial role in the differentiation process.

- Thus, while the assertion is true, the reason is not the correct explanation for it.

The correct answer is:

(b) Differentiation

Differentiation refers to the process by which the Earth separated into layers (core, mantle, and crust) based on density differences during its formation, but it is not directly related to the formation or modification of the present atmosphere.

• Solar winds played a role in stripping away the early atmosphere of lighter gases.
• Degassing refers to the release of gases, including water vapor, carbon dioxide, and other gases, from the Earth's interior through volcanic activity, which contributed to the formation of the atmosphere.
• Photosynthesis by early life forms released oxygen into the atmosphere, significantly modifying it.

Hence, differentiation is the option not related to the atmosphere's formation or modification.

Solution:

• 1. Immanuel Kant (B): Correctly matched with the original proposition of the nebular hypothesis, suggesting that planets formed from a cloud of material associated with a youthful, slowly rotating sun.
• 2. Laplace (D): Appropriately matched as he revised Kant’s hypothesis, further elaborating on the formation process and adding to the foundational nebular hypothesis.
• 3. Otto Schmidt and Carl Weizsäcker (C): Correctly paired together for their 1950 joint revision of the nebular hypothesis, adding new details about the solar nebula's composition and the process leading to planet formation.
• 4. Edwin Hubble (A): Correctly identified as the introducer of the Expanding Universe Hypothesis, which revolutionized our understanding of the universe by asserting its constant state of expansion.

- Assertion (A) is true; the Big Bang Theory does propose that the universe is expanding from a singular point of infinite density.

- Reason (R) is false because while Edwin Hubble contributed to the understanding of the expanding universe, he did not present evidence for a static universe; rather, he provided evidence for an expanding universe.

- Therefore, the assertion is true, but the reason is false.

- Statement i is correct as the initial atmosphere was indeed primarily hydrogen and helium, which were stripped away by solar winds.

- Statement ii is incorrect; photosynthesis actually increased the levels of oxygen in the atmosphere, not decreased it.

- Statement iii is correct; volcanic eruptions contributed significantly to the composition of the atmosphere by releasing water vapor and gases.

- Statement iv is correct; the oceans did form as water vapor condensed and collected in depressions on the Earth's surface within 500 million years.

Thus, the correct answer is Option D: i, iii, and iv.

The correct sequence of events in the formation of planets based on the provided text is as follows:

Step 2: The formation process begins with gravitational forces creating a core within a gas cloud.
Step 4: Around this core, a rotating disc of gas and dust develops.
Step 1: As the gas cloud condenses, small-rounded objects form around the core, which through cohesion become planetesimals.
Step 3: These planetesimals undergo accretion, where numerous smaller bodies combine due to collisions and gravitational attraction to form fewer, larger bodies, eventually becoming planets.

Statement I is true because the Big Bang Theory suggests that all matter and energy were once concentrated in a singularity before the universe expanded. Statement II is false because galaxies did not form due to a uniform distribution of matter and energy; instead, the uneven distribution led to the gravitational forces necessary for galaxy formation.