Early and modern theories

Correct answer: B. Extremely hot and dense

The Big Bang model describes the early universe as extremely hot and dense; it then expanded and cooled. This is more accurate than describing its initial condition only by size.

Correct answer: A. Protostar

As the gas-and-dust cloud collapsed, it formed a protostar. The protostar became the Sun after conditions in its core allowed sustained nuclear fusion.

Correct answer: B. Tidal Hypothesis

The Tidal Hypothesis proposed that the gravitational pull of a passing star drew material from the Sun, from which planets could form.

Correct answer: A. By the accumulation of small solid bodies

In the Planetesimal Hypothesis, small solid bodies called planetesimals accumulated and joined to form larger bodies, including planets.

Correct answer: A. It increases

The correct answer is A. On large scales, the expansion of space increases the average separation between galaxies that are not held together by gravity. Bound systems, such as some nearby galaxy pairs, do not necessarily expand with the universe.

Correct answer: A. Gas and dust cloud → flattened disk → small bodies → planets

The correct answer is A. A cloud of gas and dust collapsed and flattened into a rotating disk. Dust and rock in the disk gathered into small bodies, which accreted to form planets.

Correct answer: A. Nebular and Tidal hypotheses

The correct answer is A. The Nebular and Tidal hypotheses are historical explanations proposed for the origin of the Solar System and Earth; the other pairs concern unrelated topics.

Correct answer: A. Big Bang Theory

The correct answer is A. The Big Bang model describes the universe evolving from an early hot, dense state and expanding over time. The other options concern processes on Earth, not the universe as a whole.

Correct answer: A. The universe expanded from an early hot, dense state

The correct answer is A. The Big Bang model describes the universe expanding from an early hot, dense state. A passing star is associated with a historical tidal hypothesis, while planetesimals and a solar nebula concern Solar System formation.

Correct answer: A. A star passed close to the Sun and its gravity pulled out solar material

The correct answer is A. In the historical Tidal Hypothesis, a star passing close to the Sun was thought to raise tides and pull material from it, from which planets could form. This is a historical proposal, not the modern accepted model of Solar System formation.

Correct answer: A. Planets form through the accumulation of small bodies

The correct answer is A. The Planetesimal Hypothesis proposes that small solid bodies, called planetesimals, accumulated to form planets. The other choices describe cosmic expansion or an Earth process, not this hypothesis.

Correct answer: A. A rotating cloud of gas and dust

The correct answer is A. The Nebular Hypothesis describes the Solar System forming from a rotating cloud of gas and dust, which collapsed and flattened into a disk. The other choices are unrelated to this astronomical explanation.

Correct answer: C. Big Bang Theory

The correct answer is C. The cosmic microwave background is relic radiation from the hot early universe, now observed as microwaves. Its existence is an important line of evidence supporting the Big Bang model.

Correct answer: A. The Sun formed at the centre of a flattened gas-and-dust disk, while material in the disk accreted to form planets

The correct answer is A. In the modern solar-nebula model, a rotating cloud of gas and dust flattened into a disk. The Sun formed near its centre, and material in the surrounding disk accumulated into planets. The other statements do not describe this model.

Correct answer: A. Many relied on limited observations and could not explain all the evidence

Many early theories were developed when observations and scientific evidence were limited. As a result, they could not explain all the features of the Earth and solar system that later evidence helped scientists investigate.

Correct answer: A. They can be tested against observations and measurements

Observations and measurements allow scientists to test whether a theory fits what is seen and measured. Evidence can therefore support a theory, lead to its revision, or show that it needs to be replaced.

Correct answer: A. Big Bang, expansion and cooling, then formation of galaxies

In the standard cosmological account, the universe began in the Big Bang and then expanded and cooled. Much later, matter gathered under gravity to form stars and galaxies; this option gives that broad sequence in simplified form.

Correct answer: D. Laplace — Big Bang theory

Laplace is associated with the nebular hypothesis, not the Big Bang theory. The other pairings are standard associations: Chamberlin and Moulton with the planetesimal hypothesis, Kant with an early nebular hypothesis, and Hubble with evidence for the expansion of the universe.

Correct answer: A. Tidal hypothesis

The tidal hypothesis, associated with Jeans and Jeffreys, proposed that a nearby star's gravitational pull drew material from the Sun. The material was then thought to condense into planets.

Correct answer: A. Identify each theory's main idea and the scientist or scientists associated with it

A theory's central idea and its associated scientist or scientists help distinguish it from other theories. For example, linking Kant with an early nebular hypothesis helps identify the theory being described.

Correct answer: A. Many early theories relied on more limited observations, while modern theories are tested against a wider range of evidence

Many early proposals were made with fewer observations available. Modern theories can be tested against a much wider range of observations and measurements, although scientific theories remain open to revision when new evidence appears.

Correct answer: A. Accretion

The correct answer is A, accretion. Small particles collide and stick together, gradually building larger bodies that can grow into planets.

Correct answer: B. Big Bang Theory

The correct answer is B, the Big Bang Theory. It describes the universe expanding from an initially very hot, dense state; the question does not require the idea of a literal point.

Correct answer: C. Sun

The correct answer is C, the Sun. In the solar nebula model, matter concentrated and condensed at the centre to form the Sun, while planets formed from material around it.

Correct answer: A. Nebular Hypothesis

Nebular Hypothesis links the solar system with a nebula of gas and dust. Exam tip: rotating gas dust cloud points to nebular hypothesis.