Star formation, formation of planets, and our solar system

In differentiation heavy iron and nickel move inward to form the core. Exam tip: link formation of Earth's layers with this.

Meteorites provide information about old solar system materials. Exam tip: remember them as evidence for age and composition.

Planets hold a large share of the solar system's angular momentum through their orbital motion. Exam tip: treat mass and angular momentum as different ideas.

Because planets formed from a rotating disk their orbits are nearly in one plane. Exam tip: remember disk and orbit together.

During contraction gravitational energy changes into heat. Exam tip: understand this as the reason for a hot protostar.

A main sequence star gives energy through stable fusion. Exam tip: remember a protostar as the stage before a stable star.

Metals and silicates could remain solid at higher temperatures. Exam tip: connect inner planets with rock and metal.

Beyond the frost line temperature was low so ice could remain. Exam tip: link outer planet composition with the frost line.

Solar wind removed light gases from inner regions. Exam tip: remember this reason for the rocky nature of inner planets.

The governing concept is accretion, the gradual growth of a body through repeated collisions and gravitational merging. In the young Solar System, dust and rock particles joined to form planetesimals. Continued impacts caused these smaller bodies to combine into increasingly larger objects called protoplanets, which later developed into planets. Therefore, option C is correct. The process did not make planets shine by themselves; planetary light is mainly reflected sunlight. It also did not transform planets into galaxies, which are enormous systems containing stars, gas, and dust. Finally, the Sun remained the central star, not a satellite. Accretion thus explains both the collision process and the increase in planetary size.

More matter gathered at the center to form the Sun and planets began in the disk. Exam tip: remember the center disk matching.

Fusion in the core is necessary for a stable star. Exam tip: identify final star formation by fusion.

The interstellar medium provides gas and dust for new stars. Exam tip: call it the birth material of stars.

Meteorites give evidence of old solar system materials. Exam tip: remember meteorites for age estimation.

Jupiter's strong gravity prevented asteroids from easily joining into a large planet. Exam tip: remember the link between asteroid belt and Jupiter.

In differentiation heavy materials sank inward and lighter materials stayed above. Exam tip: use this to understand Earth's layers.

Direct answer: B, development of the early atmosphere. Outgassing means the release of gases from Earth’s hot interior through volcanic activity and related processes. These gases included water vapour, carbon dioxide, nitrogen and other substances. Their release created and changed the early atmosphere; later cooling allowed water vapour to condense and helped form oceans. Option A, the asteroid belt, formed from leftover material in the solar system, not mainly from gases escaping Earth. Option B directly names the result of outgassing. Option C, the birth of the Sun, happened earlier during solar-system formation and was not caused by Earth’s gases. Option D is unrelated: outer planets did not disappear because of outgassing. Memory cue: outgassing means gases out, atmosphere starts.

The giant impact theory links the Moon with debris from a large body colliding with Earth. Exam tip: remember this hypothesis for Moon formation.

Radioactive decay increased internal heat in early Earth. Exam tip: remember collisions compression and radioactive heat together.

Planets with higher mass can bind more small bodies. Exam tip: connect number of satellites with planetary gravity.

A planet must clear its orbit along with revolving around the Sun. Exam tip: use this to distinguish it from a dwarf planet.

Both are linked with icy bodies of the outer solar system. Exam tip: treat the Kuiper Belt as relatively nearer and the Oort Cloud as very distant.

Solar wind and radiation push a comet's gas dust away from the Sun. Exam tip: remember the tail direction away from the Sun.

Most mass is in the Sun but planetary orbital motion holds much angular momentum. Exam tip: treat both as separate facts.

Similar direction indicates origin from a common rotating disk. Exam tip: link same direction and same plane with nebular theory.