Early and modern theories

Correct answer: B. Differentiation

Heavy materials such as iron and nickel moved toward the center due to density. In exams, connect metals and density with differentiation.

Correct answer: A. Heat increase and possibility of internal differentiation

The governing concept is the thermal evolution and internal differentiation of the early Earth. During its formation, repeated impacts by planetesimals and meteorite-like bodies converted kinetic energy into heat. Radioactive decay inside the young planet supplied an additional internal heat source. Together, these processes helped keep the early Earth partly molten or highly heated for a long period. In such conditions, denser materials such as iron could move downward while lighter silicate materials rose, creating the possibility of layered internal structure. Option A is correct because it states both the heating effect and its consequence for differentiation. Option B is unrelated and much too immediate, while options C and D do not follow from these heat-producing processes.

Correct answer: A. In the molten state, materials could move according to density

The molten state allowed heavy and light materials to separate. In exams, treat melting as a condition for layer formation.

Correct answer: A. It brings gases from Earth's interior and supplies material for the early atmosphere

Gas release brought out water vapour and other gases. In exams, connect outgassing with atmosphere formation.

Correct answer: A. Widespread photosynthetic life had not developed then

Free oxygen increased later through biological processes. In exams, do not treat the early atmosphere like the present one.

Correct answer: A. Earth cooled, water vapour condensed, rain and water bodies formed

The hydrosphere means all the water found on Earth, including oceans, rivers, lakes, groundwater and water vapour. In the early stage, Earth was extremely hot, so water could remain mainly as vapour. As the surface and atmosphere cooled, the vapour could change into liquid water. This basic connection between cooling, condensation and the formation of water bodies is the central idea.

The correct sequence is that Earth cooled first, water vapour condensed next, and the resulting water fell as rain and collected in low areas to form oceans, lakes and other reservoirs. Therefore, option A gives the complete and logical chain. Option B reverses the order of important events, while the red shift and steady-state ideas do not explain hydrosphere formation. The supplied answer is consistent.

Correct answer: A. A stable surface formed where water could remain

The solid crust provided a base for hydrosphere and surface development. In exams, connect crust with water retention.

Correct answer: A. A gradual result of geochemical and later biological processes

The early atmosphere had little free oxygen and it increased later. In exams, treat atmospheric evolution as gradual.

Correct answer: A. It shows that the early solar system was active with impacts

The giant impact idea links Moon formation with large impacts. In exams, connect it with the active state of early Earth.

Correct answer: A. It is based on known decay of radioactive isotopes

Radioactive decay rates give a scientific basis for age estimation. In exams, connect Earth's age with an evidence-based method.

Correct answer: A. Big Bang, solar nebula, differentiation

Big Bang is at universe scale, solar nebula at solar-system scale, and differentiation at Earth scale. In exams, identify scale.

Correct answer: A. When the question mentions a passing star pulling matter from the Sun

A passing star and matter pulled from the Sun are clues of the tidal theory. In exams, identify theories through clue words.

Correct answer: A. When the question gives gas-dust cloud, gravitational collapse, and flat protoplanetary disk

These clues identify the modern solar nebula model. In exams, identify gas-dust cloud and disk together.

Correct answer: A. When the question asks the process of formation of Earth's internal layers

Earth's internal layers are explained by differentiation, not only by the Big Bang. In exams, write the process at the correct scale.

Correct answer: A. Planet formation is a physical process and origin of life is a later biochemical process

A planet first forms through physical processes, and life develops later. In exams, do not mix the two stages.

Correct answer: A. Internal layers by differentiation, atmosphere by outgassing, hydrosphere by condensation

Different Earth spheres developed through different processes. In exams, match process and sphere correctly.

Correct answer: A. Moving from old nebular and tidal ideas to the more evidence-based modern solar nebula model

New evidence and better physical understanding improve theories. In exams, treat science as evidence-based and changeable.

Correct answer: A. Old theories were more based on limited observations while modern models are supported by more evidence and physical processes

Modern theories are more evidence-based and broadly explanatory. In exams, clearly state the basis while comparing.

Correct answer: A. Incomplete explanation of rotational and orbital angular momentum distribution between Sun and planets

The old nebular model could not fully explain some physical distributions. In exams, remember the limitation with meaning.

Correct answer: A. Red shift and background radiation, Big Bang theory

Red shift and background radiation are major supports for the Big Bang. In exams, connect evidence with the correct theory.

Correct answer: A. Modern solar nebula model, because it links gas-dust disk, accretion, orbits, and planetary composition

The modern solar nebula model explains many solar-system observations together. In exams, write the model with its reason.

Correct answer: A. Density-based differentiation and lighter silicate materials remaining above

Lighter silicate materials remained above and helped develop mantle and crust. In exams, connect core, mantle, and crust with density-based differentiation.

Correct answer: A. It is a cosmic-level event while Earth formed later in solar-system evolution

The Big Bang explains the beginning of the universe, not Earth's direct formation. In exams, identify the scale of the theory first.

Correct answer: B. The Sun formed at the center and planet-forming material remained in the disk

Gravitational collapse concentrated matter at the center and left the remaining material in a disk. In exams, write the separate roles of center and disk.

Correct answer: C. The shift of light from distant galaxies toward red indicates their recession

Red shift indicates galaxies moving away. In exams, write the reasoning from evidence to conclusion.