Interior of the Earth
* The earth is made up of several different layers of material.
* The outermost layer is the crust.
The crust is classified into:
* Oceanic crust that consists of sima
* Continental crust that consists of sial
* The next year is highly viscous and is called the mantle.
* The mantle is the thickest layer and forms 83% of the volume of the earth.
* The outer core is made of nickel and iron, and is called Nife.
* The material in this layer is in a liquid state.
* The inner core is solid and has very temperature and pressure.
Mountains
* A mountain is a high natural landform that projects above the surrounding land.
* Mountains arranged in a line form a mountain range.
Three main types of mountains:
* Fold Mountains
* Block Mountains
* Volcanic Mountains
* Glaciers in the mountain are source of water for any rivers.
* Mountains act as storehouses of water for human beings.
* River valleys and terraces are used for cultivation of crops.
* The rich variety of flora and fauna, and the steep terrain of mountains attract tourists.
Introduction
* A variety of landforms are found on the earth.
Landforms are made by the processes:
* Internal process
* External process
* These processes can be explained through the structure of the lithosphere.
* The lithosphere is broken up into lithosphere or tectonic plates.
* As a result of the movement in the mantle, the tectonic plates move in relation to one another.
* The internal process is uplifting and sinking of the earth’s surface at various places.
* The external process involves erosion and deposition.
* Erosion refers to the continuous wearing down of the earth’s surface.
* Deposition leads to rebuilding of earth’s surface.
Landforms can be broadly classified as:
* Mountains
* Plateaus
* Plains
* A mountain is natural landforms that project above the surrounding land.
* A plateau is an elevated flat land having one or more sides with steep slopes.
* Plains are broad, large stretches of level land.
Plateaus
* A plateau is an elevated land with a flat top bound by steep slopes one or more sides.
* A plateau is also called a table land.
* The Tibet Plateau is the highest plateau in the world.
* Plateaus are formed by lava, rivers or wind.
* Plateaus are rich in mineral deposits, such as gold and iron.
* Plateaus generally have several waterfalls.
* Lava plateaus have a high percentage of productive black soil.
* Tourists are attracted to plateaus for the beautiful scenery, flora and fauna.
Plains
* Plains are large stretches of flat land, not more than 200 m above sea level.
* Plains are a result of the erosion caused by rivers and their tributaries.
* The flatness and rich sediments of plains is suitable for mechanisation of crop production.
* The flat land helps people to build houses.
* It is easier to live on plains than in the mountains.
* Human beings need to be careful in their use of land so that it can be used by future generation as well.
Rocks and Minerals
* A rock is a natural mass of minerals found within the earth’s crust.
* Minerals are substances that have a definite chemicals composition and occur freely in nature.
Rocks can be:
* Igneous
* Sedimentary
* Metamorphic
* Igneous or primary rocks are formed when molten lava cools down.
* Igneous rocks can be extrusive or intrusive.
* Sedimentary rocks are formed when large rocks break down, and the small fragments form layers and later get hardened.
* When igneous and sedimentary rocks are subjected to great heat or pressure they may morph into metamorphic rocks.
Rock Cycle
* Metamorphic rocks which are still under great heat and pressure melt to form molten magma.
* All the rocks melt and change into magma.
* Magma cools down to form igneous rocks.
Volcanoes
* Lava is molten rocks or magma that comes out from the magma chamber through the vent.
* The vent is a hole in the middle of a volcanic mountain.
* The vent is connected to the pool of lava under the earth’s surface which is known as the magma chamber.
* When the accumulated lava and ash that come out from the magma chamber cool down and solidify in layers, a volcano is formed.
* Mauna Loa in the Hawaii Islands is the world’s largest volcano.
Volcanoes can be categorised into:
* Active Volcano
* Dormant Volcano
* Extinct Volcano
* Based on shape, Volcanoes may be categorised as shield volcanoes, cinder cone volcanoes or composite Volcanoes.
Major Landforms – Work of Water
* The exogenic movements responsible for the creation of landforms are weathering, erosion and deposition.
* Weathering involves the breakdown of rocks and soils on the earth surface, whereas erosion involves the loosening and carrying away rock debris formed by weathering.
The work of the water of a river results in the formation of :
* Waterfalls
* Meanders
* Ox – bows lakes
* Floodplains
* Levees
* Distributaries
* Deltas
The erosion and deposition by sea waves leads to the creation of:
* Sea caves
* Sea arches
* Stacks
* Cliffs
* Beaches
Major Landforms – Work of Ice and Winds
Glaciers are rivers of ice.
* Glaciers pick up and carry soil and loose stones along with the ice. The forced movement of this material with the glacier can cause deep scratches and large holes to be carved in the bedrock.
* As the ice melts, these holes get filled with water, and form picturesque lakes in the mountainside.
* When the material carried by the glacier gets deposited, it leads to the formation of glacial moraines.
* Wind erosion leads to the formation of sand dunes, mushroom rocks and loess.
* Sand dunes are low, hill – like structures formed by the erosion and deposition of sand by the wind in the desert.
Earthquakes – Some Natural Phenomena
* Earthquakes are caused by a disturbance deep inside the earth’s crust.
* Earthquakes tend to occur at the boundaries of the earth’s tectonic plates. These boundaries are known as seismic or fault zones.
* Earthquakes are the phenomena experienced during sudden movement of the earth’s crust.
* The destructive energy of an earthquake is measured on the Richter scale. An earthquake measuring 7 or more on the Richter scale can cause severe damage to life and property.
* Earthquakes can cause floods, tsunami and landslides.
* The power or the magnitude of an earthquake is expressed in terms of magnitude on scale called Richter scale.
* The strongest earthquake ever recorded was in Chile on May 22, 1960. It measured 9.5 on the Richter scale.
* The point where an earthquake originates is called the focus.
* The epicentre is the point on the earth’s surface that is directly above the focus.
* Seismic waves are recorded by an instrument called the seismograph.
Measures for protection against earthquakes:
* Build quake – safe homes. Use light material like mud or timber for construction.
* Fix cupboards and shelves to the walls
* Ensure that tall building maintain fire – fighting equipments.
If an earthquake occurs:
* If at home, take shelter under some heavy furniture or stay in bed, till the tremors stop.
* Keep away from tall and heavy objects that may fall down.
If you are outdoors when an earth quack occurs
* Stay away from building, trees and overhead power line.
* Drop flat on to the ground.
* If in a vehicle, drive slowly to a clear spot and stay inside till the shaking subsides.