INTERNAL STRUCTURE OF EARTH
Important Points:
- The distance between Earth’s surface and its centre is 6371km.
- Crust depth varies from about 16km to 40km.
- Mantle depth is around 2900km.
- Upper mantle temperature is 2000 C.
- Lower mantle temperature is 3000 C.
- Outer core temperature is 3800 C and depth around 2250km.
- Inner core temperature is 5200 C and depth around 1220km.
Short Questions:
Define Geography
Geography is the scientific study of aerial variations and similarities from place to place on the surface of the Earth.
How do scientists get information about internal structure of Earth?
Scientists take help from earthquake waves, magnetic force of the earth, and gravitational force.
How many layers of earth are there?
Earth is composed of three layers i.e., Crust, Mantle, and core.
Define Earth’s crust.
Outer most part of the earth at which oceans and continents exist is known as Earth’s crust.
Describe continental crust.
It consists of various land masses known as continents. It is composed of silicon and aluminium. Therefore, it is called Sial. Its maximum depth is about 40km.
Describe oceanic crust.
Invisible part of the Earth crust under oceanic water in the form of ocean bed. It is composed of silicon and magnesium. Therefore, it is called Sima. Its maximum depth is about 8km.
Describe characteristics of Earth’s mantle.
The central layer of Earth after crust is called mantle. Upper part is in molten form whereas the lower mantle is in solid form. It is due to higher pressure of upper mantle and crust.
Describe characteristics of Earth’s core.
The inner most layer of Earth’s crust is called core. It is divided into two parts. Outer core is in liquid form and inner core is in solid form. It contains the rocks of iron and nickel and also known as Nife.
TECTONIC PLATES
Important Points:
- The ridges inside oceans are formed as a result of volcanism.
- An example of transform fault is the San Andreas Fault in western USA.
Short Questions:
What is Pangea?
Millions of years ago all the continents were joined together in a single giant super continent. It was named Pangea by a scientist named Wegener.
Name some major tectonic plates of Earth.
Pacific plate, African plate, Eurasian plate, North American plate, South American plate, Indo-Australian plate, Antarctic plate.
Why tectonic plates always remain in motion?
Earth crust is solid that is floating at the upper part of mantle that is molten. Hence, these plates are not static but always remain in motion.
Define Faults.
A crack on the Earth’s crust is created due to movement of tectonic plates. This crack is called a fault.
Name different types of faults.
Convergence plate faults, divergence plate faults, and transform faults (lateral plate contact).
Define convergence plate fault.
The movement of tectonic plate towards each other is termed as convergence plate fault.
Define divergence plate fault.
The movement of tectonic plate away from each other is termed as divergence plate fault.
Define volcanism.
Due to formation of divergence plate fault, lava emerges from weaker parts of Earth’s crust. This process is known as volcanism.
Define transform fault.
When tectonic plates slide away from each other, this is termed as transform plate fault.
How can we identify boundaries of tectonic plates?
Faults are natural boundaries between different tectonic plates that can be seen in the form of folded mountains, volcanic mountains, and centres of earthquakes.
What is Pacific Ring of Fire?
Pacific plate is surrounded by volcanic mountains from all sides and maximum volcanic activity is observed in this region because faults are present on all sides. Thus, it is called pacific ring of fire.
ROCKS
Important Points:
- Igneous rocks are the earliest which came into being and are called primary rocks.
- If magma solidifies in vertical cracks, it is called dyke.
- If magma solidifies horizontally in cracks, it is called sill.
- Gabbro, Diorite and Dolerite are examples of intrusive igneous rocks.
- Basalt and obsidian are examples of extrusive igneous rocks.
- Limestone, Brecia, Sandstone, Shale are examples of clastic rocks.
- Peat, Lignite, Anthracite, Bituminous are types of coal and example of non-clastic rocks.
- Gypsum and Rock salt are examples of chemical rocks.
Short Questions:
Define rocks.
Rock is an aggregate of minerals that may be hard like granite or soft like chalk.
How are igneous rocks formed?
Igneous rocks are formed by the solidification of molten material and magma in and outside the surface of Earth.
How are intrusive igneous rocks formed?
Intrusive igneous rocks are formed by the solidification of molten material and magma in the surface of Earth.
How are extrusive igneous rocks formed?
Extrusive igneous rocks are formed by the solidification of molten material and magma outside the surface of Earth.
How are sedimentary rocks formed?
Sedimentary rocks are formed on the surface of Earth by the weathered and eroded material layer by layer fixed together firmly with the passage of time.
How many types of sedimentary rocks are there? Name them.
There are three types of sedimentary rocks i.e., inorganic rocks (clastic rocks – consist of metallic particles, minerals and rock material), organic rocks (non clastic rocks – consist of fossils of animals and plants), and chemical rocks (made in result of some chemical process).
How are metamorphic rocks formed?
When igneous or sedimentary rocks change their physical and chemical properties due to extreme temperature and high pressure, they form metamorphic rocks.
Briefly describe regional metamorphism.
Due to convergence of tectonic plates, the lower layer experiences high temperature and pressure which changes their physical and chemical properties. This process is known as regional metamorphism. For example, shale.
Briefly describe contact metamorphism.
Due to volcanism, magma tries to come to Earth surface and rocks in cracks experience high temperature and pressure which changes their physical and chemical properties. This process is known as contact metamorphism. For example, marble.
rock cycle and uses of rocks
Short Questions:
Briefly describe the process of rock cycle.
The rock cycle describes the process through which the three main rock types (igneous, sedimentary and metamorphic) transform from one type into another.
LONG QUESTIONS:
Explain some uses of different rocks in modern era.
- Gypsum and limestone are used in cement industry. Gypsum is also used in fire extinguishers.
- Salts are used to make medicine, bleaches, and soaps. It is also used in food.
- Chalks are used in educational institutions to write on big black boards.
- Marble is used in building and mosques decoration and beautification.
- Quartz is melted to make glass that is used in construction, utensils, and mirrors.
- Coal is used for thermal energy to power engines, generators, cooking, and heat in winter.
- Mineral rock like diamond is used for jewellery, cutting and grinding.
- Mineral rocks like gold, copper, silver are used in electrical wiring and coins.
Modern techniques in Geography
Important Points:
- GIS stands for Geographical Information System. Digital mapping is done by GIS.
- The field of map designing is known as cartography.
- The person who designs maps is called cartographer.
- RS stands for Remote Sensing.
- GPS stands for Global Positioning System.
Short Questions:
Describe the importance of GIS.
GIS is computer-based approach to capture, store, manipulate, analyse, and display geographical information. It provides the foundation of digital mapping.
How does remote sensing work?
Remote sensing is a monitoring of physical properties of any area through radiations and image is formed by bouncing back of radiation which are captured by satellites.
Why is GPS an integral part of modern-day travel?
GPS helps people in positioning and travelling. Signals from different satellites are received on Earth by different control stations. User receives that information through a GPS – enabled device.
Why is Google Maps so important for modern day travel?
Google map is an internet-based utility that uses GPS to route emergency services, delivery of goods, and travellers onto their exact destination.