Download Notes za Geography Form five 5 advanced level new syllabus, kidato cha tano. Notes za Geography Form five 5, there is a collection of short notes which are good to understand concepts of this chapter for free download in PDF.
FUNCTION OF ATMOSPHERE
1) Insulation
Atmosphere is an insulator it acts as a shield or blanket and therefore regulates temperature during the night and during the winter.
2) Filtration
The atmosphere is the filter. It filters solar insulation and percent ultra violet rays of certain length due to the presence of ozone layer in the stratosphere.
3) Scientific function. Atmosphere is the scientific field
– It is the field through which the scientific experiments and observation carried out. Example ionosphere layer of atmosphere reflects some electromagnetic waves and ration signals back to the earth.
4) It supports much on hydrological cycle.
The surface water, evaporation, condensation and precipitation formation take place in the atmosphere.
5) It supports life some gases particularly oxygen is important for living organisms
– Air has weight which contributes to the occurrence of atmospheric pressure variations without which breathing would be impossible.
– Wind movement and direction that balances temperature, humidity and precipitation also result from pressure variations.
MATERIALS OF THE EARTH’S CRUST.
The earth’s crust is composed of different materials ranging from elements, minerals and rocks. These materials differ in their physical and chemical composition.
ELEMENTS
They refer to the smallest particles of matter which cannot be split into different forms by any means. Examples of elements are magnesium, potassium, sodium, iron, aluminum and silicon.
MINERALS
They are naturally occurring substances which have definite shape, colour and resistance formed due to combination of different elements. They are formed as a result of the combination of two or more elements. Some single elements like gold, silver and diamond may occur as minerals.
| MINERAL | ELEMENT |
| Quartz | Silicon and Oxygen |
| Feldspar | Potassium Sodium calcium and aluminium |
ROCK
A rock is an aggregate of minerals in a solid state. On the other hand, the term rock can include substances like clays, shells, sandstones and corals. Rocks which contain metallic compounds are called ores.
| ROCKS | MINERALS |
| Limestone | Mica, Calcite, Iron ore and feldspar |
| Granite | Mica, Iron ore, Quarts and feldspar |
| Basalt | Calcite, dolomite |
| Sand stone | Quarts, Calcite, Iron ore and feldspar |
ROCK TYPES AND THEIR CLASSIFICATION
Rocks are aggregates of minerals in a solid state. Examples of rocks are such as lime stone, granite, basalt, sand
stone and shale. Rocks can be classified depending on various criteria such as mode of formation, texture, structure, colour, permeability, age and the degree of resistance.
Rocks can be classified as follows:
1) A: ACCORDING TO THE MODE OF FORMATION (GENETIC)
Rocks can be classified into: –
Igneous Rock
Sedimentary rock
iii. Metamorphic rocks
IGNEOUS ROCKS
These are rocks which are formed by the cooling and solidifying of the molten material from the interior of the earth. The molten materials can solidify either intrusively or extrusive. When molten materials are still in the earth’s crust are formed as magma but when they reach on the earth’s surface are called lava.
CLASSIFICATION OF IGNEOUS ROCKS
Igneous rocks can be classified into two criteria;
1) According to the place of occurrence
2) According to chemical composition.
1.According to the place of occurrence, igneous rocks can be classified
a) Intrusive rocks
These are igneous rocks formed when the molten materials cool and solidify within the earth. The cooling and solidification of the molten materials can be near the surface or very deep in the crust. Igneous rocks formed when molten materials cool and solidify near the surface are called hypabyssal igneous rocks. Examples include granite, porphyries, and dolerite. These rocks can be exposed to the surface if there is severe erosion. Some rock masses like lopolith, laccolith, photolith, sill and dykes are also hypabyssal igneous rocks.
When molten materials cool and solidify deep in the crust, they form plutonic igneous rocks. These rocks consist of large grains and they are hard since they cool and solidify slowly. Examples include Granite, diorite, gabbro, pumice, and peridotite.
b) Extrusive rocks
These are igneous rocks formed when the molten material solidifies on the earth’s surface and form lava. These rocks have small grains because they cool and solidify fast due to low temperature on the earth’s surface.
Hypabyssal igneous rocks
These are rocks formed when the magma cools and solidifies closely or nearly to the earth’s surface. They have medium size particles, example dolerite.
Plutonic igneous rocks
These are formed when the molten material (magma) solidifies deep down in the crust. They are consisted of large grains and they are hard because of the slow cooling process for example granite, diorite, gabbro etc
According to Chemical composition, igneous rocks can be classified into;
i) Felsic (acidic) igneous rocks: These are igneous rocks which consist of great amount/content of silica and feldspar with a very little or no iron or any other metallic metal for example gramorphyte, granite etc
ii) Mafic (basic) igneous rocks: These are igneous rocks which consist of small amount of silica with large amount of magnesium, iron and other minerals like aluminum.
iii) Ultra mafic (ultra-basic): These are rocks which consist of a very large amount of metallic minerals like iron, magnesium and little amount of silica less than 45% for example peridotite.
iv) Intermediate igneous rocks: These are igneous rocks with silica content between basic and acidic degree. That is both acidic and basic oxides are in equal proportions.
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