RBSE Solutions Class 10 Science Chapter 15 Structure of Earth

I. Multiple Choice Questions

Question 1. Which of the following is not a name of earth?
(a) Land
(b) Gaiya
(c) Red planet
(d) Terra
Answer: (c) Red planet
In simple words: The Earth is sometimes called "Terra" or "Gaiya," but "Red planet" is the name for Mars because of its distinct reddish appearance.

🎯 Exam Tip: Remember common names for planets; Earth is often referred to by various names in different cultures and languages.

Question 2. How much of the earth's surface is covered with water?
(a) 70%
(b) 30%
(c) 50%
(d) None of the options
Answer: (a) 70%
In simple words: A very large part of the Earth's surface, about seventy percent, is covered by water, mostly in oceans and seas. This makes our planet look blue from space.

🎯 Exam Tip: Knowing the approximate proportions of land and water helps understand Earth's environment. Water covers most of the surface.

Question 3. Which element is in maximum abundance on earth?
(a) Silicon
(b) Gold
(c) Oxygen
(d) Iron
Answer: (d) Iron
In simple words: The most common element found in the entire Earth, including its core, is iron. The dense core of our planet is largely made of iron and nickel.

🎯 Exam Tip: When answering about "abundance on Earth," consider the entire planet, not just the crust, as the core contains massive amounts of heavy elements.

Question 5. What causes tides?
(a) Sun
(b) Moon
(c) Both
(d) Sun and moon aligning along a line
Answer: (d) Sun and moon aligning along a line
In simple words: Tides happen because of the gravitational pull from both the Moon and the Sun on Earth's oceans. When the Sun, Earth, and Moon are in a straight line, their combined gravity makes the tides stronger.

🎯 Exam Tip: Remember that both the Sun and Moon influence tides, but the Moon has a stronger effect because it is much closer to Earth.

Structure of Earth Very Short Answer Type Questions

Question 6. What is the reason for solstices on earth?
Answer: Solstices on Earth are caused by the Earth's tilt on its axis. As the Earth orbits the Sun, its tilted axis means that one hemisphere is pointed more directly towards the Sun, leading to longer days and warmer temperatures.
In simple words: Solstices happen because Earth's axis is tilted. This tilt makes different parts of Earth get more direct sunlight at different times of the year, causing seasons and the longest/shortest days.

🎯 Exam Tip: The Earth's axial tilt, combined with its orbit around the Sun, is key to understanding seasons and solstices.

Question 7. Earthquake is measured on which scale?
Answer: Earthquakes are measured on the Richter scale. This scale helps scientists understand the strength, or magnitude, of an earthquake by looking at the seismic waves it creates.
In simple words: Earthquakes are measured using the Richter scale. It tells us how strong an earthquake is by giving it a number.

🎯 Exam Tip: Always associate the Richter scale with measuring earthquake magnitude or strength. Do not confuse it with intensity scales.

Question 8. Where are tectonic plates situated?
Answer: Tectonic plates are located in the crust of the Earth. These massive plates make up the Earth's outermost layer, called the lithosphere, and they are constantly moving very slowly.
In simple words: Tectonic plates are found in the Earth's outer shell, which is called the crust. These huge pieces of the crust are always moving.

🎯 Exam Tip: Understanding that tectonic plates are part of the Earth's crust is fundamental to comprehending geological events like earthquakes and volcanoes.

Question 9. What causes tsunami?
Answer: A cyclone is a type of powerful storm that forms over warm ocean waters, characterized by low pressure at its center and strong winds spiraling inwards. Cyclones can bring heavy rain and strong winds.
In simple words: A cyclone is a huge storm with strong winds that spin around a calm center, forming over the sea.

🎯 Exam Tip: Remember that cyclones are rotating weather systems associated with severe weather, bringing high winds and heavy rainfall to coastal areas.

Structure of Earth Short Answer Type Questions

Question 11. What will be the situation after earthquake above the scale 7 Richter at a place?
Answer: An earthquake with a magnitude of 7 or more on the Richter scale is extremely damaging. Such powerful earthquakes often cause widespread destruction to homes and large buildings. They can also trigger landslides, leading to significant loss of human lives and property in the affected area.
In simple words: An earthquake stronger than 7 on the Richter scale causes huge damage. It can destroy buildings, cause landslides, and lead to many deaths and loss of belongings.

🎯 Exam Tip: For high-magnitude earthquakes, focus on the scale of destruction, including infrastructure damage, geological impacts like landslides, and human casualties.

Question 12. What are ocean currents?
Answer: Ocean currents are like vast rivers flowing within the ocean. The water in these currents moves in a specific direction. Some ocean currents carry warm water, while others carry cold water. Unlike land rivers, ocean currents are not formed by land slopes but by differences in water temperature and density, as well as wind.
In simple words: Ocean currents are like big, moving rivers in the sea. They carry warm or cold water in a steady direction, driven by differences in heat and how heavy the water is.

🎯 Exam Tip: Emphasize that ocean currents are large-scale movements of water driven by temperature, salinity (density), and wind, playing a crucial role in global heat distribution.

Question 13. What is the benefit of weathering forces in agriculture?
Answer: Weathering forces are very helpful for agriculture because soil, which is essential for growing crops, is created by these forces. Large, flat lands ideal for farming are often formed through the work of weathering agents. Also, many important minerals that enrich the soil come out of rocks as they break down due to weathering.
In simple words: Weathering helps agriculture by making soil from rocks. This creates fertile land for farming and releases minerals that plants need to grow.

🎯 Exam Tip: Highlight the direct link between weathering and soil formation; without weathering, fertile topsoil necessary for agriculture would not exist.

Question 14. Name four factors which help in weathering.
Answer: Two factors that help in weathering are:
(a) Temperature
(b) Rain
In simple words: Temperature changes and rain are two key things that help break down rocks into smaller pieces over time.

🎯 Exam Tip: Even if a question asks for a specific number of items, always present all the items provided in the source answer. Clearly list each factor with its label.

Question 15. How did the moon come into existence?
Answer: The Moon is believed to have formed about 4.4 billion years ago. Scientists think that a large celestial body, similar in size to Mars, collided with Earth. This huge impact caused material to be ejected into space, which then gathered to form the Moon. The Moon is the only natural satellite orbiting our planet.
In simple words: The Moon formed when a big object like Mars hit Earth a long, long time ago. Pieces broke off and came together to make the Moon, which is Earth's only natural helper in space.

🎯 Exam Tip: The leading theory for the Moon's formation is the "Giant Impact Hypothesis," which explains its composition and orbital characteristics.

Structure of Earth Long Answer Type Questions

Question 16. With the help of a suitable diagram, explain the internal structure of earth.
Answer: The Earth is made up of three main layers: the crust, mantle, and core. Scientists define the boundaries of these layers based on their chemical makeup and physical properties. Generally, the deeper you go, the denser and hotter the material becomes.

• Crust: This is the outermost solid layer of the Earth. Its thickness varies, which is why we have mountains and oceans. The crust can be thought of as having two parts: the lithosphere (land) and the hydrosphere (water). The atmosphere is usually included with the lithosphere. Most of the lithosphere is soil, and the area where living things exist, including parts of the lithosphere, hydrosphere, and atmosphere, is called the biosphere.
• Mantle: This is the second layer of the Earth, lying beneath the crust. It is the thickest layer and mostly consists of hot, molten rocks, mainly silicate rocks with high amounts of iron and magnesium. This layer moves slowly, like bubbles in boiling water, causing it to vibrate in the Earth's middle part.

In simple words: Earth has layers: a thin crust on top, a thick mantle of hot, melted rock in the middle, and a very hot core inside. Each layer is different in what it's made of and how it behaves.

🎯 Exam Tip: When describing Earth's internal structure, clearly define each layer (crust, mantle, core) and mention their composition, state (solid/liquid), and relative thickness. A clear diagram is essential for full marks.

Question 17. What do you understand by internal moulding forces of earth? Explain any two of them.
Answer: Internal molding forces are those processes that occur deep inside the Earth and are not visible from the surface. These forces arise from the expansion and contraction of rocks due to high temperatures within the Earth, and also from the movement of hot, molten magma. Over long geological periods, these forces continually reshape the Earth's surface.

When these internal forces act perpendicular to the Earth's layers, some parts of the crust rise to form elevated regions, while others sink, creating deeper areas. This leads to the formation of continents, islands, plateaus, plains, and ocean basins on the surface. Sedimentary rocks that form in the oceans can also be pushed up to become part of the continents.

When internal molding forces act horizontally, they create waves within the Earth's crust. These waves cause significant shaking of the rocks, resulting in folds, fractures, and fissures on the surface, which eventually form mountains and valleys.

In simple words: Internal molding forces are hidden movements inside Earth that change its shape. They come from hot rocks expanding or magma moving. These forces can push land up to make mountains or pull it down to make valleys, constantly reshaping our planet over time.

🎯 Exam Tip: To explain internal molding forces, remember to discuss their origin (heat, magma movement) and their two main directions of action (perpendicular for vertical shifts, horizontal for folds/faults), connecting these to major landforms.

Question 18. What is erosion? Explain the significance of any two forces of erosion on human life.
Answer: Erosion refers to external forces that move substances from one place to another on Earth. Examples of these forces include moving air (wind), flowing water (rivers), and ice (glaciers). Erosion is a continuous process that shapes landscapes.

Significance of wind on human life:

• Wind influences weather patterns, impacting daily life in many important ways.
• Wind has traditionally aided in the navigation of ships, allowing movement across seas.
• Wind energy is now captured and used to generate electricity, providing clean power.
• Wind slowly changes the landforms around us, moving sand and soil.

Significance of river:

• Rivers constantly change the landforms along their path, carving valleys and depositing sediment.
• Rivers have always been vital for human civilization, with many great societies developing and flourishing along their banks due to access to water and fertile land.

In simple words: Erosion is when natural forces like wind and water move soil and rocks from one place to another. Wind affects our weather and helps make electricity, while rivers shape the land and have always been important for human towns and farming.

🎯 Exam Tip: When explaining erosion, define it as the transportation of materials and provide clear examples of natural agents. For significance, give concrete, distinct points for each force's impact on human activities or the environment.

I. Multiple Choice Questions

Question 1. What is the age of earth?
(a) 1 billion years
(b) 3 billion years
(c) 4.5 billion years
(d) 7 billion years
Answer: (c) 4.5 billion years
In simple words: The Earth is very old, about 4.5 billion years. Scientists figured this out by studying rocks and meteorites.

🎯 Exam Tip: The age of the Earth is a fundamental geological fact, often determined through radiometric dating of rocks and other planetary materials.

Question 2. Which is the largest terrestrial planet in the Solar System?
(a) Earth
(b) Mars
(c) Venus
(d) Mercury
Answer: (a) Earth
In simple words: Among the rocky planets closest to the Sun, Earth is the biggest one. Terrestrial planets are those made mostly of rock and metal.

🎯 Exam Tip: Remember that terrestrial planets (Mercury, Venus, Earth, Mars) are rocky, while the outer planets are gas or ice giants. Earth is the largest of the terrestrial group.

Question 3. Earth is composed of how many layers?
(a) One
(b) Two
(c) Three
(d) Four
Answer: (c) Three
In simple words: The Earth is made of three main layers: the crust, the mantle, and the core. These layers are defined by their different materials and densities.

🎯 Exam Tip: When asked about Earth's main layers, always recall the crust, mantle, and core as the fundamental divisions of its internal structure.

Question 5. The inner core of earth is mainly composed of which element?
(a) Iron
(b) Gold
(c) Nickel
(d) Platinum
Answer: (a) Iron
In simple words: The very center of the Earth, its inner core, is mostly made of iron. This iron core helps create Earth's magnetic field.

🎯 Exam Tip: The inner and outer cores are primarily composed of iron (and some nickel), which is crucial for Earth's magnetism and internal heat.

Question 6. Most devastating earthquakes happen along which type of tectonic plate boundary?
(a) Constructive
(b) Convergent
(c) Conservative
(d) None of the options
Answer: (b) Convergent
In simple words: The strongest and most damaging earthquakes usually occur where tectonic plates are pushing into each other, called a convergent boundary. This intense collision causes huge pressure buildup and sudden releases of energy.

🎯 Exam Tip: Convergent plate boundaries, where plates collide, are typically associated with the most destructive earthquakes and volcanic activity due to intense forces and subduction.

Question 7. Which state of India lies in the low risky zone of earthquake inspite of that suffered from devastating earthquake in 1737?
(a) Jammu & Kashmir
(b) Uttarakhand
(c) Himachal Pradesh
(d) West Bengal
Answer: (d) West Bengal
In simple words: Even though West Bengal is generally in a low-risk area for earthquakes, it experienced a very strong one in the year 1737. This shows that historical events can sometimes go against general risk assessments.

🎯 Exam Tip: Historical earthquake data, even for regions generally considered low-risk, is important for understanding potential seismic hazards.

Structure of Earth Very Short Answer Type Questions

Question 1. What is volcano?
Answer: Shaking of the Earth's surface due to turbulence inside the Earth is called an earthquake. This movement happens when tectonic plates shift.
In simple words: When the Earth's surface shakes because of movements deep inside, it is called an earthquake.

🎯 Exam Tip: Always describe the cause of earthquakes as the sudden release of energy from shifting tectonic plates, leading to ground vibrations.

Question 3. What is the range of Richter scale?
Answer: The Richter scale typically ranges from 1 to 10. While there's no upper limit, earthquakes above 10 are theoretically possible but have not been observed. Each whole number increase on the scale means a tenfold increase in measured amplitude.
In simple words: The Richter scale goes from 1 to 10, showing how strong an earthquake is. Higher numbers mean much stronger shakes.

🎯 Exam Tip: Remember that the Richter scale is logarithmic, meaning each whole number increase represents a significant (32 times) increase in energy released, not just a linear increase.

Question 4. What is an agent of weathering?
Answer: Forces that break down rocks are known as agents of weathering. These agents include heat from the sun, rain, frost (freezing water), and wind. They work together over time to crumble rocks into smaller pieces.
In simple words: Things that break down rocks, like sun's heat, rain, ice, and wind, are called agents of weathering.

🎯 Exam Tip: List key natural elements that cause physical or chemical breakdown of rocks without moving the weathered material away, which differentiates it from erosion.

Question 5. What is an agent of erosion?
Answer: Agents of erosion are forces that transport materials from one part of the Earth to another. Common examples include air (wind), water (in rivers or ocean currents), and ice (in glaciers). These agents constantly reshape the Earth's surface.
In simple words: Agents of erosion are things like wind, water, and ice that move rocks and soil from one place to another.

🎯 Exam Tip: Distinguish erosion from weathering by remembering that erosion involves the *movement* of broken-down material, not just the breakdown itself.

Question 6. What is a tide?
Answer: A tide is the regular rise and fall in the level of ocean water. This phenomenon happens at predictable times each day, affecting coastal areas worldwide.
In simple words: A tide is when the ocean water goes up and down in a regular pattern every day.

🎯 Exam Tip: Remember that tides are a natural, periodic phenomenon related to gravitational forces and are distinct from irregular sea level changes like tsunamis.

Question 7. What causes tide?
Answer: Tides are caused when the Moon and the Sun align in a straight line with the Earth. This alignment creates a strong gravitational pull on the ocean water, causing it to bulge outwards in some areas and recede in others, resulting in high and low tides.
In simple words: Tides happen because the Moon and Sun pull on Earth's water with their gravity. When they line up, this pull is stronger and causes the water to rise and fall.

🎯 Exam Tip: The primary cause of tides is the gravitational force of the Moon, with the Sun also playing a significant, though secondary, role.

Structure of Earth Short Answer Type Questions

Question 2. Write a short note on earth's crust.
Answer: The Earth's crust is its outermost solid layer. Its thickness varies significantly across the globe, which is why we have both towering mountains and deep oceans. The crust can be broadly divided into the lithosphere (landmasses) and the hydrosphere (water bodies). The atmosphere is often considered an extension of the lithosphere. Most of the lithosphere is composed of soil. The biosphere, where all living things are found, includes parts of the lithosphere, hydrosphere, and atmosphere.
In simple words: The crust is Earth's hard, outer layer. It's not the same thickness everywhere, creating mountains and oceans. It includes land, water, and air where life exists.

🎯 Exam Tip: When describing the crust, highlight its varying thickness, its role in creating landforms, and its connection to the concepts of lithosphere, hydrosphere, atmosphere, and biosphere.

Question 3. Write a short note on mantle of earth.
Answer: The Earth's mantle is the second layer, located beneath the crust. It is the thickest layer, mostly composed of hot, molten rocks called silicates, which are rich in iron and magnesium (more so than in the crust). Within the mantle, hot material rises and cooler material sinks, similar to bubbles forming in boiling water. This convection causes the mantle to slowly move and vibrate, influencing the movement of tectonic plates.
In simple words: The mantle is the thick, middle layer of Earth, made mostly of hot, melted rock. It moves slowly, like thick boiling water, and this movement affects the Earth's surface.

🎯 Exam Tip: Focus on the mantle's composition (silicate rocks, iron, magnesium), its semi-molten state, and the convection currents within it, which are critical for plate tectonics.

Question 4. Write a short note on core of earth.
Answer: The Earth's core is the innermost part of our planet and is the hottest region due to immense heat trapped during Earth's formation. Temperatures can reach about 7000 degrees Celsius. Evidence shows that the core is gradually cooling. It is divided into two parts: the outer core and the inner core. The outer core is liquid and primarily consists of iron and nickel, while the inner core is solid, mainly composed of iron, and also contains elements like gold and platinum.
In simple words: Earth's core is its super hot center, split into two parts. The outer core is liquid iron and nickel, and the inner core is solid iron, keeping a lot of heat inside the planet.

🎯 Exam Tip: For the core, remember to mention its extreme temperature, primary composition (iron and nickel), and the distinction between the liquid outer core and the solid inner core.

Question 5. What do you understand by volcano?
Answer: A volcano is a unique geological feature created by internal molding forces. It is essentially an opening in the Earth's crust that allows hot, molten rock (magma), ash, and gases to escape from below the surface. This process causes turbulence within the Earth's interior and is a powerful force that continually reshapes our planet's landscape.
In simple words: A volcano is a mountain with a hole that lets out hot, melted rock, ash, and gases from deep inside the Earth, causing big changes on the land.

🎯 Exam Tip: Define a volcano as an opening in the Earth's crust through which magma, ash, and gases erupt, highlighting its connection to internal geological forces.

Question 6. What do you understand by Richter scale?
Answer: The Richter scale is used to measure the intensity, or magnitude, of an earthquake. It uses a device called a seismograph to record the ground motion. The scale ranges from 1 to 10, though there is no theoretical upper limit. Earthquakes up to 4 on the Richter scale are generally weak and often go unnoticed. Those up to 5.5 are considered strong, while anything above 7 is classified as devastating, causing widespread destruction.
In simple words: The Richter scale is a tool that measures how strong an earthquake is, from 1 to 10. Small earthquakes might not be felt, but those above 7 cause a lot of damage.

🎯 Exam Tip: Explain that the Richter scale is a logarithmic measure of earthquake magnitude, where each whole number increase represents a significant jump in the energy released, leading to greater destructive potential.

Question 7. Write a short note on tsunami.
Answer: A tsunami is a Japanese word meaning "harbor wave." It refers to large ocean waves caused primarily by underwater earthquakes, especially those with a magnitude greater than 7 on the Richter scale occurring at the ocean floor. Tsunamis travel outwards in two main directions from their origin: towards the coast and into deeper parts of the ocean. The waves heading towards the coast can cause immense destruction, with debris carried by the tsunami destroying life and property even far inland.
In simple words: A tsunami is a giant ocean wave, usually caused by a strong earthquake under the sea. It travels fast and can cause huge damage when it hits the coast, washing away everything.

🎯 Exam Tip: Emphasize that tsunamis are typically caused by large underwater earthquakes, not surface weather, and highlight their destructive power upon reaching coastal areas.

Structure of Earth Long Answer Type Questions

Question 1. What causes earthquake? Explain tectonic plate theory.
Answer: Earthquakes are primarily caused by an imbalance in the Earth's internal structure. This imbalance can result from natural factors like pressure from groundwater in aquifers or from human activities such as underground explosions. The most common explanation for earthquakes is based on the tectonic movement theory.

The Earth's crust is made up of about 29 tectonic plates, with six being the most significant. These plates are constantly, though very slowly, moving. All geological molding activities, like mountain formation and volcanic eruptions, happen along the edges of these plates. Tectonic plate boundaries are of three main types:

• Transform boundary: Plates slide past each other (conservative).
• Divergent boundary: Plates move apart (constructive).
• Convergent boundary: Plates crash into each other (destructive).

Highly destructive earthquakes mostly occur along convergent or destructive boundaries where plates collide. For example, the collision of plates is considered the main reason for earthquakes in regions like northern India, Tibet, and Nepal. Earthquakes also occur at other types of plate boundaries, but their mechanisms can be more complex to explain.

In simple words: Earthquakes happen when Earth's huge plates, called tectonic plates, move and crash into each other. These plates are always shifting, and when they rub or push hard, the ground shakes. The biggest shakes happen where plates collide directly.

🎯 Exam Tip: Explain earthquakes by linking them directly to tectonic plate movement. Describe the three types of plate boundaries and specify why convergent boundaries are associated with the most destructive seismic events.

Question 3. What is glacier? What is the effect of global warming on glacier?
Answer: A glacier is a massive, persistent body of dense ice that moves slowly under its own weight. It is essentially a thick slab of ice in constant motion across land.

Effect of global warming on glaciers: Global warming refers to the ongoing increase in the Earth's average temperature in recent years. This warming significantly impacts glaciers, causing them to melt at a faster rate than new ice is formed. Consequently, glaciers are shrinking in size worldwide. The melting of glaciers contributes to a rise in global sea levels, putting many coastal cities at risk of gradually becoming submerged by the ocean.
In simple words: A glacier is a big, slow-moving river of ice. Global warming, which is Earth getting hotter, makes glaciers melt much faster than they can grow. This melting causes sea levels to rise, threatening cities by the sea.

🎯 Exam Tip: When defining a glacier, emphasize its movement and dense ice composition. For global warming's effect, focus on the increased melting rate, glacier shrinkage, and the resulting rise in sea levels, linking these environmental impacts.

Question 4. What is ocean current? What is the significance of ocean current?
Answer: Ocean currents are also known as "rivers flowing in the ocean." These are continuous, directed movements of seawater. Some ocean currents carry warm water, while others carry cold water. Unlike land rivers, ocean currents are not driven by the slope of the land but by factors like temperature differences, water density, and wind. These currents also bring a lot of moisture and cause rainfall at higher altitudes. In places where a warm current meets a cold current, large temperature differences occur, which can lead to powerful storms like hurricanes or typhoons. Additionally, ocean currents significantly influence the navigation of ships and the survival and distribution of sea creatures.
In simple words: Ocean currents are like big rivers in the sea that move water around, some warm, some cold. They help create rain, cause big storms where warm and cold water meet, and are important for ships to travel and for sea animals to live.

🎯 Exam Tip: Define ocean currents as continuous, directed movements of seawater. Explain their significance by detailing their roles in climate regulation (temperature, rainfall, storms), marine life, and human activities like shipping.