Early and modern theories

Correct answer: D. When it depends on a rare event and does not satisfactorily explain orbital facts

A rare event and weak orbital explanation become limitations of a theory. In exams, connect acceptance of a model with evidence and explanation.

Correct answer: B. Both linked the origin of the solar system with nebular material

Both ideas were early attempts toward explaining solar system formation from a nebula. In exams, place them in the nebular category.

Correct answer: A. Because conversion of rings into stable planets is not clear under all physical conditions

Laplace's idea was historical, but modern physical explanation is more complex. In exams, separate the old idea from its limitation.

Correct answer: C. Planetary growth by accretion

Joining of small bodies resembles the modern process of accretion. In exams, identify the relation between old terms and modern processes.

Correct answer: A. Such a close astronomical event is considered very rare

The tidal theory depends on a rare close passing-star event. In exams, write probability as a limitation of the theory.

Correct answer: C. Because it explains planetary orbits, composition, and leftover bodies together

This model connects many observations through one process. In exams, treat broad explanation as its strength.

Correct answer: D. Inner rocky planets and outer gaseous planets

Near the Sun, rocky materials remained, while in colder outer regions gases and ices remained more. In exams, connect temperature, distance, and composition.

Correct answer: B. It explains where icy materials could condense and join planet formation

Beyond the frost line, accumulation of ices and light gases was easier. In exams, connect it with the composition of outer planets.

Correct answer: A. Ordered motion of planets in a similar direction

Bodies formed from one rotating disk show similarity in motion. In exams, link angular momentum with orbital order.

Correct answer: B. Because it is a theory of the universe's origin and expansion

The Big Bang is a cosmological theory, and Earth formed later through solar system evolution. In exams, write the scale difference.

Correct answer: C. The universe had an early hot phase and expansion

Red shift is evidence of expansion and background radiation of an early hot state. In exams, connect both with the Big Bang.

Correct answer: B. To keep average density constant despite expansion

The steady state theory assumed formation of new matter during expansion. In exams, remember average density and continuous creation together.

Correct answer: C. Cosmic microwave background radiation

Background radiation is considered a remnant of the early hot universe. In exams, take it as evidence against the steady state theory.

Correct answer: A. Accretion adds mass and differentiation separates materials according to density

Accretion formed Earth, while differentiation formed its internal layers. In exams, do not mix the two processes.

Correct answer: B. They sank toward the center and helped form the core

The governing concept is density differentiation during the early development of Earth. When the young Earth was sufficiently hot and partly molten, materials could separate according to density. Heavy metallic elements, especially iron and nickel, moved downward under gravity toward the centre, while lighter silicate materials remained nearer the outside and contributed to the mantle and crust. Option B is correct because sinking dense matter helped establish the core and Earth’s layered internal structure. Option A is physically and geologically incorrect, C confuses solid planetary materials with surface water, and D mistakes physical separation for a transformation of matter into light.

Correct answer: C. It allowed materials to separate according to density

In the molten state, heavy and light materials could move to different levels. In exams, write melting and differentiation together.

Correct answer: A. Because they added both mass and heat

Impacts contributed to Earth's accretion and hot state. In exams, connect impacts with formation processes too.

Correct answer: B. Internal melting and differentiation

Heat from radioactive decay helped maintain internal temperature. In exams, connect heat sources with layer formation.

Correct answer: A. Because internal gases came out and helped develop atmosphere and hydrosphere

Gas release supplied water vapour and other gases. In exams, connect atmosphere and hydrosphere with outgassing.

Correct answer: A. Because free oxygen was very low in the early atmosphere

Water vapour and carbon dioxide were important in the early atmosphere. In exams, keep it different from the present atmosphere.

Correct answer: A. Early Earth was dynamic and affected by large impacts

This hypothesis connects a giant impact with Moon formation. In exams, consider the early solar system active and impact-rich.

Correct answer: C. Decay of radioactive isotopes

Radiometric dating estimates age based on radioactive decay. In exams, connect age determination with scientific evidence.

Correct answer: B. Accretion, heating, differentiation, crust formation, outgassing

Earth first formed by accretion, and then internal and outer spheres developed. In exams, keep the sequence correct.

Correct answer: A. To explain the dynamic arrangement of matter in the solar nebula

Weizsäcker tried to explain planet formation through vortex-like motion in the nebula. In exams, connect him with modern planet-origin ideas.

Correct answer: C. He linked interstellar gas and dust with planet formation

Schmidt emphasized gas and dust instead of matter drawn from the Sun. In exams, identify the difference in source material.