Evolution of the earth

After life began organisms evolved gradually. Exam tip: treat biological evolution as a long-term process.

Early life was simple and developed in low oxygen conditions. Exam tip: treat early life as simple.

Ozone protected against harmful rays making land safer for life. Exam tip: connect ozone with life on land.

Early life is believed to have evolved in oceans. Exam tip: connect oceans with the beginning of life.

Falling temperature solidified the outer part and clarified layers. Exam tip: link cooling with layer formation.

Earth's evolution includes both physical and biological changes. Exam tip: study atmosphere water and life together.

Lava and gases indicated an active hot Earth. Exam tip: link it with early geological activity.

The governing concept is the hydrosphere, the Earth system that contains all naturally occurring water. It includes oceans, seas, rivers, lakes, groundwater, glaciers, ice sheets, soil moisture, and water vapour in the atmosphere. As the young Earth cooled, water vapour condensed and accumulated in depressions, forming oceans and other lasting water stores. The continuing water cycle connects these stores by evaporation, condensation, precipitation, runoff, and infiltration. Therefore, long-term accumulation of water produced the hydrosphere, making option A correct. The lithosphere is the solid rocky outer part of Earth, not its water system. A constellation or star group is an apparent arrangement of stars in the sky and has no connection with the accumulation of terrestrial water.

Earth's interior cooled slowly so it remained hot for a long time. Exam tip: distinguish cooling rate of interior and surface.

Water and atmosphere prepared life-supporting conditions. Exam tip: understand life through combined effect of spheres.

Crust water atmosphere and life developed in stages. Exam tip: identify before and after in sequence questions.

The direct answer is A: Earth’s gravity held atmospheric gases near the planet and helped the secondary atmosphere remain stable. Gravity is the attractive force associated with mass. Earth has enough mass to pull gas molecules toward it, so gases do not simply escape into space. During the formation of the secondary atmosphere, volcanic activity released gases such as water vapour, carbon dioxide, and nitrogen. Gravity helped retain these gases around Earth, while cooling and other processes later shaped the atmosphere. The reasoning is: Earth has mass → mass produces gravity → gravity attracts gas molecules → gases remain around Earth → an atmosphere can be maintained. Option A is correct because it states this retaining function. Option B is wrong because gravity does not turn gases into stone; that would be a physical and chemical transformation unrelated to atmospheric retention. Option C is wrong because gravity did not turn oceans into fire. Option D is wrong because the Moon’s orbit is not the role being asked about, and gravity did not “stop” the Moon. Gravity cannot prevent every gas from escaping, especially very light gases, but it retained enough gas for an atmosphere. Memory cue: gravity is Earth’s invisible hold on the atmosphere.

Carbon dioxide was an important part of the early atmosphere. Exam tip: treat it as a gas of atmospheric evolution.

Oceans created permanent water areas on the surface. Exam tip: view oceans as a surface change.

Early Earth was not a safe or stable place for life. It had very high temperatures, volcanic activity, frequent impacts, and an atmosphere unlike the present one. With time, the planet cooled, a more stable crust formed, water collected to make oceans, and the atmosphere gradually changed. These developments created conditions in which life could survive and evolve. Therefore, option A, saying that harsh conditions gradually became life-supporting, is correct.

The word “gradually” is central because Earth did not become modern in a single event. Its transformation occurred through many connected physical and chemical changes over a very long period. The other choices contradict basic Earth history: Earth was not always like it is today, life did not precede the formation of Earth, and oceans did form after cooling and condensation. Thus, the correct idea is a slow transition from a hot, hostile planet to a more suitable environment.

The governing concept is the lithosphere, the rigid outer part of Earth. It includes the crust and the uppermost, relatively solid portion of the mantle. Because these materials are made mainly of rocks and minerals, the lithosphere is best described as Earth’s solid rocky part. Option A is therefore correct. Water vapour and clouds belong mainly to the atmosphere and cannot define the lithosphere. Bacteria are living organisms and may occur in soil or rocks, but they are not the lithosphere itself, so option D is far too narrow. The word “mainly” is important: the lithosphere is a physical, rocky layer, not a single substance or a biological component. Its plates move over the softer asthenosphere and influence earthquakes, volcanism, and mountain building.

The governing concept is hydrosphere formation during Earth’s cooling. As the early atmosphere cooled, water vapour condensed into droplets. Repeated rainfall transferred this water from the atmosphere to the surface, where it collected in depressions and gradually formed streams, lakes, seas, and oceans. Thus option A is correct: rainfall helped accumulate water on Earth’s surface and established the surface part of the hydrosphere. Option B is impossible because rainfall is liquid water, not a process that turns a planet into gas. Option C confuses planetary water-cycle development with stellar formation, and option D is false because rainfall has no power to remove gravity. The process involved condensation, precipitation, runoff, and accumulation, not an instant transformation.

Biological changes began after life originated. Exam tip: connect biological evolution with origin of life.

Before photosynthesis free oxygen was low in the atmosphere. Exam tip: link photosynthesis with oxygen rise.

Layers show that materials became arranged separately inside. Exam tip: treat layers as a result of differentiation.

Condensation and rain brought much water vapour to the surface as water. Exam tip: remember transfer of water from atmosphere to hydrosphere.

The governing concept is the role of internal heat in geological evolution. Heat left from Earth’s formation, radioactive decay, and gravitational compression kept parts of the interior hot and mobile. This energy promoted melting, convection, and volcanic activity. Volcanoes released lava and gases, including water vapour and carbon dioxide, helping shape the early crust, atmosphere, and hydrosphere. Therefore option A is correct. Internal heat did not make the atmosphere disappear instantly, so B is false. It also could not turn oceans into stone; that contradicts the existence of liquid water. Option D is wrong because internal heat is a geological process and does not cause life to become fully developed immediately. Its influence is indirect and operates over long periods.

Gradual evolution means that life did not appear in its present variety all at once. Over a very long period, living forms changed step by step. The earliest forms were comparatively simple, while later forms showed greater complexity and variety. This idea describes a gradual process, not a sudden event or a claim that humans appeared first.

Therefore, option A is correct because it expresses the broad direction from simpler forms toward more complex forms. Option B is wrong because life did not form in one day. Option C is wrong because humans appeared much later than the earliest life. Option D is wrong because life was not restricted to mountains. The answer is A.

They show gradual development of Earth's major systems. Exam tip: treat them as main components of Earth's evolution.

The direct answer is B: joining planetesimals gradually increased Earth’s size and mass. Planetesimals were small solid bodies formed from material in the early solar system. Their repeated collisions and gravitational attraction caused accretion, meaning that smaller bodies stuck together and built a larger planetary body. The reasoning is: dust and rock fragments collect → planetesimals form → planetesimals collide and join → mass increases → the growing Earth becomes larger. Option B is correct because it describes the immediate broad result of accretion. Option A is wrong because oceans did not form immediately; Earth first became extremely hot, and oceans appeared later after cooling and condensation. Option C is wrong because modern humans evolved much later and are unrelated to the joining of planetesimals. Option D is wrong because the ozone layer did not form immediately; significant ozone depends on atmospheric oxygen and later photochemical processes. The word “gradual” is important: planetary growth occurred through many additions over time, not in one instant. Memory cue: accretion means “adding pieces to make a bigger planet.”