Evolution of the earth

Earth became life supporting through integrated gradual evolution. Exam tip: see the whole chain in broad questions.

Oceans were necessary media for pre life chemical evolution. Exam tip: place life after hydrosphere.

Complex life depended on many favourable systems. Exam tip: treat life evolution as a multi factor process.

Photosynthesis changed the direction of atmosphere and life. Exam tip: identify the atmospheric role of organisms.

The secondary atmosphere helped prepare water and gaseous conditions. Exam tip: understand indirect causes.

Internal heat kept Earth's inner activities active for a long time. Exam tip: link heat with dynamism.

Opposite positions of light and heavy materials are results of differentiation. Exam tip: study crust and core comparatively.

Interaction of atmosphere and hydrosphere affected chemical processes. Exam tip: link chemistry with interaction of spheres.

Life did not only depend on atmosphere but also changed it. Exam tip: understand two way relation.

The direct answer is A: safety for life increased in land areas. The early atmosphere did not protect life well from harmful ultraviolet radiation. When oxygen accumulated, some oxygen changed into ozone, forming an ozone layer high in the atmosphere. Ozone absorbs much of the Sun’s harmful ultraviolet radiation. Step by step: oxygen increased; ozone formed; ultraviolet danger at the surface decreased; organisms could survive more safely outside water; life could gradually expand onto land. Option A is correct because land life received greater protection. Option B is wrong because life did not become limited to Earth’s core, which is extremely hot and unsuitable for life. Option C is wrong because ozone did not destroy oceans; oceans remained important for life. Option D is wrong because ozone is part of the atmosphere and did not make the atmosphere disappear. The careful idea is not that ozone alone created all land life, but that it removed an important radiation barrier to terrestrial expansion. Memory cue: ozone means ultraviolet shield, and shield means safer land.

Rocks and fossils record Earth's ancient evolution. Exam tip: build evidence based understanding.

Water vapour of the secondary atmosphere was linked with hydrosphere formation. Exam tip: remember vapour source for hydrosphere.

Early Earth was active due to both external impacts and internal heat. Exam tip: write external and internal causes of instability.

Life supporting conditions formed from combined results of many processes. Exam tip: prioritise integrated causes.

Life and atmosphere affected each other. Exam tip: identify two way relations among Earth systems.

Hydrosphere formation followed a chain from outgassing to oceans. Exam tip: read causal sequence carefully.

Oxygen was linked with complex life and ozone protection. Exam tip: treat oxygen as a central turning point.

Earth's evolution is a combined result of physical chemical and biological processes. Exam tip: use multi causal analysis.

The direct answer is A. Earth’s evolution is a long process in which one change affects later changes. A strong study method therefore combines sequence, cause, effect and relationships between systems such as the atmosphere, hydrosphere, crust and life. Option A is correct because it helps explain both what happened and why it mattered. Option B is wrong because memorising meanings alone does not show connections or processes. Option C is wrong because present climate is only one small part of Earth’s history. Option D is wrong because disconnected facts make it difficult to understand development over time. For example, cooling led to crust formation, condensation and water accumulation, which later affected the atmosphere and life. Exam cue: write linked chains rather than isolated words.

Earth's major systems developed over a long time. Exam tip: write gradual and integrated evolution.

In a fluid-like state materials could move according to density. Exam tip: treat melting as a condition for differentiation.

When planetesimals struck the early Earth, their kinetic and gravitational energy was converted into heat. Therefore, fewer impacts would reduce a major source of Earth's early heat. Radioactive decay was a separate source of internal heat and would not stop simply because impacts became fewer. Exam tip: remember planetesimal impacts, gravitational compression, and radioactive decay as key sources of Earth's early heat.

Internal heat kept volcanic processes active. Exam tip: write the relation between heat source and outgassing.

The direct answer is B: density-based differentiation. In the early Earth, heating caused materials to separate according to density. Dense materials, especially iron and nickel, moved downward toward the centre and formed much of the core. Less-dense silicate materials remained nearer the outside and contributed to the mantle and crust. The reasoning is: different densities caused movement and separation; separation produced layers with different compositions; the core–crust difference is evidence of differentiation. Option A, photosynthesis, is a biological process in green plants and cannot explain Earth’s internal layers. Option B is correct because it describes gravitational separation by density. Option C, solar wind, is a stream of charged particles from the Sun and does not create the core’s heavy-metal concentration. Option D, condensation, means gas changing to liquid and may describe an early cooling step, but it does not specifically explain the separation of heavy core material from lighter crustal material. Memory cue: heavy sinks, light stays outward—this is differentiation.

The secondary atmosphere formed from gases released from Earth's interior. Exam tip: identify change in atmospheric sources.