Earth's Structure and Physical Geography - Class VIII

The innermost layer of the earth is known as the core. It is divided into inner core and outer core. It comprises of a high concentration of nickel and iron.

B. Erosion

Soil erosion is defined as the wearing away of topsoil. Topsoil is the top layer of soil and is the most fertile because it contains the most organic, nutrient-rich materials. One of the main causes of soil erosion is water erosion, which is the loss of topsoil due to water.

The enormous temperature difference between the top and bottom of the mantle creates convection currents that drive plate tectonic movement. Hotter material near the core rises, while cooler material near the crust sinks, creating circular motion that moves the plates above.

Oxygen and silicon are the most abundant elements in the Earth's crust. Silica (silicon dioxide) is the most common compound found in crustal rocks.

The topmost layer of the soil is called topsoil. This layer is usually fairly loose, porous, dark and rich in humus. The humus is derived from decomposed and partly decomposed organic matters of plant and animal origin in the soil. It plays important role in maintaining the fertility of the soil.

In the earth's ecological history time period which is about 55 million years old was called the primary age.

• Earth's crust is divided into 7 major and several minor tectonic plates which float on a semi-fluid layer called the asthenosphere. Hence option A is correct.

The three main layers of Earth include the crust (1 percent of Earth's volume), the mantle (84 percent), and the core (inner and outer combined, 15 percent). The outermost of all these three is the crust. 

• The average thickness of earth crust at ocean floors- 8 km 
• The average thickness of earth crust at continents- 32 km
• Thus the earth crust is thicker at continents as compared to oceans floors.

The Mohorovicic Discontinuity, or Moho is the boundary between the crust and the mantle. This boundary is located at approximately 2891 km depth beneath the Earth's surface. The boundary is observed via the discontinuity in seismic wave velocities at that depth. This discontinuity is due to the differences between the acoustic impedances of the solid mantle and the molten outer core.

Earth mainly consists of four layers namely crust, mantle, outer core and inner core.

Mantle is the widest of all the layers, which is 1800 miles thick. It is composed mostly of silicate rocks rich in magnesium and iron. It is found beneath the earth’s crust. The temperature of this layer is 1600 degrees Fahrenheit at the top to about 4000 degrees Fahrenheit near the bottom.

The Mohorovicic Discontinuity marks the lower limit of Earth's crust. It occurs at an average depth of about 8 kilometers beneath the ocean basins and 32 kilometers beneath continental surfaces. Mohorovicic was able to use his discovery to study thickness variations of the crust. He discovered that the oceanic crust has a relatively uniform thickness, while continental crust is thickest under mountain ranges and thinner under plains.

Earth mainly consists of four layers namely crust, mantle, outer core and inner core:

Crust: This is about 8 km thick inside and is highly explored. The continental crust is composed mostly of granite. The oceanic crust consists of a volcanic lava rock called basalt.

Mantle: It is the largest layer of the Earth which is 1800 miles thick. It is composed mostly of silicate rocks rich in magnesium and iron.

Outer core: It is located beneath the mantle. The outer core is composed of melted metals like nickel and iron.

Inner core: It is composed of an iron-nickel alloy and some light elements.

Layer that lies immediately after the mantle is the outer core.

The distance between the centre of earth to its surface is called earths radius.

It is approximately 6,371 km or 3,959 miles

In geology the word "discontinuity" is used for a surface at which seismic waves change velocity. One of these surfaces exists at an average depth of 8 kilometers beneath the ocean basin and at an average depth of about 32 kilometers beneath the continents. At this discontinuity, seismic waves accelerate. This surface is known as the Mohorovicic Discontinuity or often simply referred to as the "Moho."

All seismic waves do not cause earth quake. Certain magnitude is necessary to cause an earthquake.

Region on earth’s surface where earth quake can be barely detected after an occurrence of a seismic wave is called shadow region.

In the given options all are correct but the statement ‘P-wave shadow zone is larger than the S-wave shadow zone’ is false and vice versa is true.

Outer core: It is located beneath mantle. The outer core is composed of the melted metals like nickel and iron.

Inner core: It is composed of an iron–nickel alloy and some light elements.

Thus core is mostly constituted by iron. This fact can be known by the measurement of densities of various layers of earth. At the core there is a higher density and this density could only be possible by higher amounts of iron present in the core.

Seismic wave is a wave of energy caused due to sudden break or explosion of a rock in the earth’s interior.

When seismic wave passes from one material to the other material it either reflects, refracts or changes it velocity.

This phenomenon of seismic reflection or refraction enables geologists to study the interior of earth because reflection and refraction differs with the type of material.

Tectonic plates are those that are present beneath the earth surface and have been moving throughout the earth’s history.

What drives tectonic plates is not known clearly but one theory is that the convection drives heated up plates to move towards the surface and after they reach the ceiling they are deflected sideways. 

Earth’s magnetic field exerts from earth’s interior to the outer surface.

Inner core is mostly made of iron and temperature is about 5,700°C, at this temperature iron is as hot as surface of sun, but crushing pressure caused by gravity prevents it from becoming liquid and hence cannot produce magnetic field.

But the outer core has a 2,000 km thick layer of iron, nickel, and small quantities of other metals. As the pressure is lower in outer core when compared to the inner core metals exists in fluid state. 

Differences in temperature, pressure and composition within the outer core cause convection currents in the molten metal and earths spin result in whirling movements of the liquid metal resulting in generation of electric currents and there by producing magnetic field.

Earth mainly consists of four layers namely crust, mantle, outer core and inner core.

The boundary between the mantle and the core lies at a depth of approximately 2891 km or 3000km.

The core–mantle boundary of the Earth
lies between the planet's silicate mantle and
its liquid iron-nickel outer core

The earth is made up of three layers, one inside the other like an onion. They are the crust, the mental and the core. The topmost layer, that is, the crust is solid, the thinnest and the lighter. The average density is 2.75 to 2.90. The thickness is 8 to 100 km. Below this top layer is the layer of basalt rock which is heavier than the topmost layer, i.e, the mental. The average thickness is 100 2900 km and the density varies from 3.1 to 5.00. The innermost layer is the core. The core contains 1/3 of the entire mass of the world. The average density is 5.1 to 13.00.

Earth mainly consists of four layers namely crust, mantle, outer core and inner core.

Widest of all the layers of earth is Mantle which is 1800 thick. It is composed mostly of silicate rocks rich in magnesium and iron.

Basalt is dark coloured igneous rock mainly composed of pyroxene mineral. It most commonly forms as an extrusive rock, such as a lava.The oceanic crust consists of a volcanic lava rock called basalt. Oceanic crust is the thin crust underlying the oceans.

Basalt density present is equal to 3.0 g /cm'3

The crust of the earth is made up of different strata of rocks. As a result of movement inside the earth, these rock strata at times are forced up and down and thus fold mountain are created. So fold mountain are the result of large-scale earth movement caused by stresses in the earth's crust.

The oceanic crust consists of a volcanic lava rock called basalt. Oceanic crust is the thin crust underlying the oceans. Basalt is dark coloured igneous rock mainly composed of pyroxene mineral. It most commonly forms as an extrusive rock, such as a lava.

Basalt density present is equal to 3.0 g cm'3

Earth mainly consists of four layers namely crust, mantle, outer core and inner core.

Lithosphere is the rigid outer layer of the earth which includes crust and uppermost mantle.

Crust: This is about 8 km thick inside and is highly explored. The continental crust is composed mostly of granite. The oceanic crust consists of a volcanic lava rock called basalt.

Mantle: It is composed mostly of silicate rocks rich in magnesium and iron.

The topmost layer of the earth is solid, the thinnest and the lightest and is known as lithosphere. The lithosphere has two layer- the outer part and the inner part. The outer part which is immediately below the newer sedimentary formation, i.e, crust. The outer layer of lithosphere mainly found under the continent and inner layer it mostly found partly under oceans. The inner layer again has three layers, i.e, SIAL which is made of silica and aluminum. The average thickness is 8 to 100 km. The layer next to it is SIMA makeup of silica and magnesium and an average thickness of this layer is 100 to 2900 km. The innermost layer is NIFE madeup of nickel and ferrous and the density is 5.1 to 13.

• The hard resistant materials forming the earth's crust are called the rocks. Hence option A is correct
• In different types of rocks, different metals and minerals are found.
• Lava is the molten material that gets ejected out of a volcano.

• The earth's crust is the outermost layer of the earth which has cooled down while the inner layers are still burning. When things cool after burning they get wrinkled up hence the earth's crust is largely wrinkled.
• It is plain, plateau and mountainous at different places and rocky as well. The most appropriate answer is option C ie wrinkled.

• The core of the earth is made up of heavy minerals like iron and nickel hence statement in option A is incorrect which makes it the right answer.
• Rest statements are true 
• The outer core is made up of molten rocks, its estimated temperature is 3300 degrees C and the inner core acts like a solid mass.
• Note- inner core is solid and the outer core is liquid.

Fold mountains are formed due to the folding of crustal rocks by compressive forces generated by the movements inside the earth. Thus fold mountains can be said to be caused by the influence of internal forces. These are the highest and most extensive mountains of the world and are found in all the continents.

The outer or upper layer of the earth's crust is mostly found under the continent. Silica and aluminum are abundantly found in this layer therefore it is popularly known as SIAL. The average density of the layer is 2.75 to 2.90 and the average thickness is 8 to 100 km.

Mental is the middle layer of the earth lies between crust and core. The average thickness of this layer is 100 to 2900 km. Silica and magnesium elements predominate in this layer so it is known as SIMA.  Density of the layer varies between 3.1 to 5.00. It has two layers: upper mantle and lower mantle.  

Sima is the name for the lower layer of the Earth's crust. This layer is made of rocks rich in magnesium silicate minerals. Typically when the sima comes to the surface it is basalt, so sometimes this layer is called the 'basalt layer' of the crust. The sima layer is also called the basal crust or basal layer because it is the lowest layer of the crust. Because the ocean floors are mainly sima, it is also sometimes called the oceanic crust.

The Earth can be divided into four main layers: the solid crust on the outside, the mantle, the outer core and the inner core. Out of them, the crust is the thinnest layer of the Earth, amounting for less than 1% of our planet's volume

The Gutenberg Discontinuity is the boundary layer between the Earth's mantle and the outer core, characterized by a significant change in seismic wave velocity.

The Earth's interior is composed of layers based on composition and density: SIAL (crust), SIMA (lower crust/upper mantle), Asthenosphere, Mesosphere, and NIFE (core).

The innermost layer of the earth is core. This central mass mainly made of nickel and iron and therefore is known as NIFE. The density of the layer is 5.1 to 13.00. It is composed of heaviest mineral materials. The core contains 1/3 of the entire mass of the earth. It has two layers outer metallic core and inner metallic core.

The core is the innermost layer of the earth with density 5.1 to 13.00. It composed of heaviest minerals. This central mass is mainly made of nickel and iron and therefore is known as NIFE. The core contains 1/3 of the entire mass of the earth. The materials of this part may be liquid, plastic or even solid state due to tremendous pressure from above.

The Sima layer is formed of silica and magnesium. This layer is below top layer and made up of basalt rock which is heavier than the topmost layer. The density of the layer varies from 3.1 to 5.00. the average thickness of this layer is 100 to 2900 km.

• The lithosphere is the outer solid shell of the Earth and consists of all the mountains, rocks, stones, top soil and sand found on the planet.
• The lithosphere includes the crust and the uppermost layer of the mantle. It also includes all the rocks under the sea and under the surface of the Earth.

Most of the continents are formed of SiAl layer, i.e., Silica and Aluminium. The upper layer of the Earth's crust is called lithosphere and has 2 parts- upper part forms continents SiAl has a density of 2.7. The lower part is denser and is called SiMa (Silica, Iron, Magnesium).

The topmost layer of the earth is solid, the thinnest, and the lightest and is known as the lithosphere. The thickness of the lithosphere of about 100 km. It is mostly composed of granite. The lithosphere has two layers - the outer layer and the inner layer.

Sial refers to the earth’s crusts upper layer, it is made up of rocks abundant in silicate and aluminium-based minerals. The word Sial itself is an amalgam of the first two letters of aluminium and silica, Sial runs anywhere from 5-70KM deep from the surface.

The layer just below the crust is called the mantle. This layer is the layer of basalt rock which is heavier than the topmost layer. The density of this layer varies from 3.1 to 5.00. The average thickness of this layer is 100 to 2900 km. Silica and magnesium elements predominate and it is popularly known as SIMA.

The average thickness of the crust is 35 km below continents, 6 km below oceans (plus 5 km of sea water). 

The outer most or top most layer of the earth is termed as crust. The crust of the earth is consist of sedimentary and granite rocks. The average density of crust is 2.8 to 3. The outer layer of the earth mainly found under continent. 

The Earth can be divided into four main layers: the solid crust on the outside, the mantle, the outer core and the inner core. Out of them, the crust is the thinnest layer of the Earth, amounting for less than 1% of our planet's volume.

The mantle is the mostly-solid bulk of Earth's interior. The mantle lies between Earth's dense, super-heated core and its thin outer layer, the crust. The mantle is about 2,900 kilometers (1,802 miles) thick and makes up a whopping 84% of Earth's total volume.

Earth's inner core is the innermost geologic layer of the Earth. It is primarily a solid ball with a radius of about 1,220 kilometres (760 miles), which is about 20% of the Earth's radius or 70% of the Moon's radius.

Global observations show that the crustal thickness varies through the tectonic regions. While the continental crust is 30–70 km thick, the oceanic crustal thickness is 6–12 km. 

Oxygen is by far the most abundant element in the earth's crust. Scientists estimate oxygen comprises nearly half of the mass of the crust. It also accounts for 21 percent of Earth's atmosphere

By standard geographical definition, landforms that rise significantly above their surroundings, usually defined as over 900 meters, are classified as mountains.

A plateau is a flat-topped highland with steep sides, characterized by an elevation significantly higher than the surrounding plains.

Soil formation is a very slow process; it is estimated that it takes hundreds to thousands of years to form just one inch of topsoil.

Minerals are found in the Earth's crust (lithosphere) and are also dissolved in ocean water (hydrosphere), making both sources for mineral extraction.

Contour bunding is a proven sustainable land management practice for marginal, sloping, and hilly land where the soil productivity is very low. It is widely adopted by the ethnic minorities of Nepal who practice the shifting cultivation system of farming. 

The lithosphere is the rigid outer part of the Earth, consisting of the crust and upper mantle.