Geology and Earth Structure

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.

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.

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.

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 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.