The earth and its structure and tectonic movements

I. Choose the correct answer:-

1._________ is the only planet has organisms in it. Earth

2. The Pangea is broken into —— major plates.7

3. The ______________of the earth is not stable. Crust.

4. Large scale vertical movements of the earth crust are called ____________ movements. Endogenic.

5. The point of origin of the earthquake is called Focus.

II. Fill in the blanks:-

1. The continents crust is composed of granite layer.

2. The SIAL layer is floating on the SIMA layer.

3. Large scale horizontal movements of the earth crust arecalled Endrogenic movements.

4. Surface is also known as L waves.

5. A volcano is a vent or an opening in the earth crust.

III Match it:

1. Mauna loa – Hawai

2. Vesuvius – Italy

3. Kilimanjaro – Africa

4. Fujiyama – Japan

5. Norcondam – India.

IV Answer the following:

1. Name the types of layers of the earth.

v The crust

v The mantle

v The core

2. Pangea:

v A few million years ago all the present continents were clusterd together around South pole.

v This super continent was called Pangea.

Panthalassa:

v The Pangea was surrounded by a mega ocean called panthalassa. Panthalassa was otherwise known as Super Ocean.

3.Name the major plates of the world.

v Eurasia, Antarctica, North America, Pacific, South America, Africa and Indo Australian plates.

4. Name the forces which affect the Earth movements.

v Endogenic or Internal forces: Such internal forces are earthquake volcano and landslide.

v Exogenic or External forces: Such external forces are river wind, glacier and sea waves.

5.What is mean by anticline and syncline?

v Horizontal movements of the earth crust make folding and displacement of the layers of rocks.

v Simple folding consists of alternating upfolds called Anticlines and downfolds called synclines.

6.What are the types of volcanoes?

v Active volcano

v Dormant volcano

v Extinct volcano.

V Distinguish between:

1. SIAL

v The sontinental crust is composed of a layer.

v It is made up of of silica and aluminium.

v The average depth of sial is about 20 k.m.

SIMA

v The oceanic crust is composed of basaltic layer.

v It is made up of silica and magnesium.

v The average depth of sima is about 25 k.m..

2.Crust

v The upper most layer of the earths surface.

v It is also called as lithosphere.

v It is divided into sima and sial.

CORE

v The inner most layer of the earth surface.

v It is also called as Baryspere.

v This divide into inner core and outer core.

3. Dormant

v They are called sleeping volcanoes.

v These volcanoes have been active in the past stopped erecting lava now, but it can erupt at any time in the future. Eg. Vesuvius in Italy.

EXTINCT

v They are called dead volcanoes.

v These volcanoes erupted in the past but they did not do so recently and in future it is expected there will not be any eruptions. Eg. Kilimanjaro in Africa.

4. Endogenic forces and exogenic forces.

v It originates and acts from within the earths crust.

v It gives rise to deformation and irregularities on the crust of the earth.

v These movements which bring about vast changes on the crust of the earth.

v It originates and acts on the surface.

v It removes the irregularities to made a leveled on and below the crust.

5.Primary waves and secondary waves:-

v P-waves moves faster and are the first to be recorded by the seismograph.

v It can travels through gaseous liquid and solid materials.

v It travels at a speed of 8k.m./sec.

v S – Waves are slower than the P-waves.

v It can travel through solid materials.

v It travels at a speed of 5k.m./sec.

VI. Answer in briefly.

1. Name the layers of the earth and explain the crust in detail.

Layers of the earth

v Crust mantic core sial upper mantle upper core sima lower mantle lower core.

v The uppermost layer of the earths surface is called the crust.

v The continental crust is composed of a layer called the sial  which is made up of silica and Aluminum.

v The oceanic crust is composed of basaltic layer layer called the  sima which is made up of silica and magnesium.

v Crust is thicker on the continents and thinner in the ocean floor.

v The sial layer is floating on the sima layer.

v The average depth of sial is about 20 k.m.

v The average depth of sima is about 25 k.m.

v The average density of the crust is about 3gkm.

2. Describe the types of earthquakes waves.

Earth quake waves are divided into body waves and surface waves.

Body waves:-

Body waves are produced by the release of energy at the focus and move in all directions.

These are two types of body waves.

1.Primary waves or p-waves

2.Secondary waves or s-waves.

Primary waves:-

v P-waves move faster and are the first to be recorded by the seismograph.

v It can pass through gases, liquids and solids.

v It travels at a speed of 8k.m./sec.

Secondary waves:-

v S-waves are slower than the p-waves. It can travel through solid materials.

v During the occurrences of secondary waves, particles oscillate in the directions of wave travel.

v It travels at a speed of 5k.m./sec.

Surface waves.

v These waves are the last to be recorded on the seismograph.

v These Waves cause most of the damages on the surface.

v They are called as L-waves.

v They travel at a speed of 4km/sec.

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