Early and modern theories

The correct answer is A. The Steady State Theory proposed that the universe’s large-scale appearance stays the same over time, even as it expands; it proposed continuous creation of matter to maintain this condition.

The correct answer is C. The Big Bang model is the widely accepted framework for explaining the universe’s early hot, dense state and its subsequent expansion.

The correct answer is D. The Big Bang model describes an expanding universe: on large scales, distances between unbound galaxies increase over time.

The correct answer is A. The recession of distant galaxies is evidence that the universe is expanding. This supports the expanding-universe picture described by the Big Bang model; it does not mean that all galaxies are moving away from a single point through space.

The correct answer is B. During Earth’s formation, colliding bodies and the accumulation of material released gravitational energy as heat, helping to make the young Earth very hot.

The correct answer is C. Earth grew gradually as small solid bodies collided and accumulated through accretion; it did not form from a ready-made ocean or continent.

The correct term is nebula. In studies of the origin of the Solar System, a nebula is a vast cloud of gas and dust. Under gravity, parts of such a cloud may contract, rotate, and flatten into a disc from which the Sun and planets can form. Therefore option D directly matches the definition in the question. A plateau is an elevated flat-topped landform, a delta is sediment deposited at a river mouth, and a catchment is an area from which water drains to a common outlet. These are geographical surface features or drainage terms, not clouds involved in planetary formation. The word “nebula” should therefore be associated with gas, dust, and the early Solar System.

The Tidal Hypothesis proposes that the gravitational pull of a passing star drew material from the Sun, which later condensed into planets. That passing-star interaction is the clue to option A.

The Planetesimal Hypothesis proposes that small solid bodies, called planetesimals, accumulated to form planets. Therefore, option B matches the process described.

Accretion is the gradual accumulation of material: particles and smaller bodies collide and join, building larger bodies that can develop into planets. This is why option C is correct.

The Big Bang Model describes the universe expanding from an early hot, extremely dense state. It is not an explosion into empty space; the model describes the expansion of the universe itself. Therefore, option D is correct.

The Nebular and Planetesimal Hypotheses are both early proposals about how the Solar System formed. The other choices name unrelated Earth-science or social phenomena, so option A is correct.

The Big Bang Theory describes the universe expanding from an early hot, dense state. That account of cosmic expansion identifies option B.

The Big Bang Theory describes the expansion of the universe from an early hot, extremely dense state. This matches option C; it does not describe the Sun emerging from Earth or a permanently static universe.

The Nebular Hypothesis proposes that the Solar System formed from a nebula of gas and dust, with material in the nebula eventually forming the Sun and planets. Therefore, option D is correct.

The Planetesimal Hypothesis proposes that small bodies called planetesimals accumulated to form planets, including Earth. This is the role of small bodies described in option A.

Edwin Hubble is especially associated with observations relating galaxy distances to their recession speeds, which supported the idea that the universe is expanding. Earlier redshift observations by other astronomers also contributed, so Hubble should not be taken as the sole source of all such evidence. Option B is the best answer.

The rotating nebula flattened into a disk around the central mass. Material in this disk could come together to form planets, so rotation helped make planet formation possible.

The Big Bang model describes the universe as expanding from an initially hot, dense state. This distinguishes it from the listed hypotheses about the formation of the solar system.

In the modern nebular model, a cloud of gas and dust collapsed. The proto-Sun formed at its centre, while a surrounding disk supplied material that came together to form planets.

Immanuel Kant proposed an early nebular idea for the origin of the solar system in 1755. Laplace later developed the nebular hypothesis; Jeans is associated with the tidal hypothesis, not the Big Bang Theory.

The proposed process and the scientist associated with it are meaningful clues: for example, Kant is linked with an early nebular idea, while Jeans is linked with the tidal hypothesis. Option length or position does not identify a theory.

The correct answer is C, cosmic microwave background radiation. It is relic radiation from the early universe, released when the universe became transparent; the expansion of the universe has since stretched it to microwave wavelengths. Its existence supports the Big Bang model.

The correct answer is D. As the rotating cloud of gas and dust that formed the Solar System collapsed, rotation and collisions among its particles helped flatten it into a disk. The planets formed from material in this disk, so their orbits lie nearly in the same plane.

According to the Nebular Hypothesis, the solar system formed from a vast rotating cloud of gas and dust. Gravity caused this material to contract, leading to the formation of the Sun and planets. A solid mountain, ocean water, and a glacier are features that form on Earth, not the original material of the solar system. Exam tip: Link the phrase “cloud of gas and dust” with a nebula.