Early and modern theories

Correct answer: C. Explaining formation of stable separate planets from rings

Laplace's ring idea was simple but did not clearly explain the full physics of planet formation. In exams, separate historical idea and modern limitation.

Correct answer: D. Small solid bodies joining to form larger bodies

Accumulation of planetesimals resembles modern accretion. In exams, remember the sequence from small bodies to larger planets.

Correct answer: A. As a tide-like effect pulling matter from the Sun

A passing star was assumed to create tidal pull on the Sun. In exams, connect the word tidal with gravitational pull.

Correct answer: B. Condensation of extremely hot matter into stable planets is considered difficult

It is physically difficult for hot solar matter to easily form stable planets. In exams, remember the hot-matter problem.

Correct answer: C. Angular momentum of the original rotating nebula

Bodies formed from the same rotating disk show similar motion. In exams, connect angular momentum with orbital order.

Correct answer: D. Difference between inner rocky planets and outer gaseous-icy planets

Beyond the frost line, accumulation of ice and gases was more possible. In exams, study temperature, distance, and planet composition together.

Correct answer: A. Near the Sun, light gases could not remain easily and heavy materials could persist

In the hot inner region, rocky and metallic materials persisted more. In exams, treat inner planets as dense rocky planets.

Correct answer: B. Retention of gases and ices in colder outer regions of the solar nebula

Outer regions were colder, so gases and ices could accumulate more. In exams, connect outer planets with large gaseous planets.

Correct answer: C. Rotation and gravitational collapse

The direct answer is C: rotation and gravitational collapse. A protoplanetary disk begins as a large cloud of gas and dust. Gravity pulls the material inward, so the cloud collapses and becomes smaller. At the same time, the cloud rotates. As it contracts, conservation of angular momentum makes the rotation faster, and collisions and motion tend to spread material into a flattened rotating disk around the young Sun. Therefore C is correct: both gravitational collapse and rotation are important parts of the process. Option A, soil erosion and deposition, occurs on planetary surfaces and does not form a protoplanetary disk. Option B, phases of the Moon, are caused by the changing portion of the Moon lit by the Sun as seen from Earth; they do not flatten a cloud of cosmic matter. Option D, ocean tides and ebbs, are caused mainly by gravitational effects of the Moon and Sun on oceans and are not the process that creates the early disk. The reasoning chain is: gas and dust cloud → gravity causes collapse → rotation increases during contraction → material forms a flattened disk. Memory cue: “collapse pulls inward; rotation spreads into a disk.”

Correct answer: D. It is the modern solar nebula model

The Sun at the center and planet material in the disk identify the modern solar nebula model. In exams, read clues in sequence.

Correct answer: B. Big Bang theory

This radiation is considered a remnant of the early hot universe. In exams, treat background radiation as Big Bang evidence.

Correct answer: C. Continuous creation of new matter

The steady state theory proposed continuous creation of matter. In exams, identify it separately from the Big Bang.

Correct answer: D. Big Bang assumes an early hot state while steady state assumes average uniformity

Big Bang has a beginning and expansion, while steady state has average uniformity and continuous creation. In exams, remember the basic contrast.

Correct answer: A. Planet formation by solar nebula and accretion in the solar system

The Big Bang explains the beginning of the universe, while Earth formed later in the solar system. In exams, identify scale and sequence.

Correct answer: B. Galaxies and stars

Large cosmic structures formed by gravitational concentration of early matter. In exams, connect structure formation with gravity.

Correct answer: C. Chemical evolution of the early universe

After the Big Bang, light elements formed and later became the basis for stars. In exams, connect chemical evolution with cosmic sequence.

Correct answer: D. First accretion formed Earth's mass, then differentiation formed layers

Accretion builds the planetary body and differentiation organizes its interior. In exams, do not reverse the order.

Correct answer: A. Heavy materials moved toward the center and lighter materials stayed above

Density-based differentiation formed the arrangement of core, mantle, and crust. In exams, remember heavy elements and core together.

Correct answer: B. Because in molten state materials could move according to density

In molten Earth, heavy materials could sink and lighter ones rise. In exams, treat melting as a condition for differentiation.

Correct answer: C. Both supplied heat and helped melting and differentiation

Both heat sources kept Earth hot and dynamic. In exams, connect heat sources with internal layers.

Correct answer: D. Because gases came out from Earth's interior and formed the early atmosphere

Outgassing released water vapour, carbon dioxide, and other gases. In exams, connect gas release with atmosphere.

Correct answer: A. Widespread photosynthetic life developed later

The early atmosphere did not have oxygen like today. In exams, connect free oxygen with a later biological stage.

Correct answer: A. Water vapour cooled and changed into liquid water and rain

On a cooler Earth, water vapour condensed and helped develop water bodies. In exams, remember cooling and hydrosphere together.

Correct answer: C. The Moon formed from material ejected after a large body collided with early Earth

The giant impact idea connects Moon origin with the impact-rich early Earth. In exams, identify it as a modern idea.

Correct answer: D. Because it uses radioactive isotope decay to estimate the age of rocks and meteorites

Radiometric method is a basis of scientific age determination. In exams, connect Earth's age with radioactive decay.