Physical geography can be simply defined as the study of the structure of the Fath and the forces which affeet it, These forces are categorized into two kinds: intemal and external forces. Internal forces are forces which act within or beneath the Barth's crust. These forces result nto various Earth movements such as vertical and horizontal movements, vulcanicity and earthquakes. External forces are forces which act inside the earth's surface and result into

various geomorphic processes such as mass wasting and weathering, The earth is composed of inner and outer zones (layers). The outer layer of the earth comprises of the atmosphere, biosphere and hydrogphere, while the inner layer includes the erust, mantle and core The Earth's Crust, The Mantle, The Core and their Respective Characteristics Concentric Zones of the Earth Identify concentric zones of the earth The earth is composed of three intemal, concentric layers of increasing densities. These layers

are the erust, mantle and core. They are made up of different layers of socks, with their densities increasing towards the eentre of the earth, That is, densities of rocks that make up the carth increase as you move from the surface towards the interior

The Crust (Lithosphere)

This is the outermost part of the earth. It consists of silica and aluminium (sil), It forms the upper layer of the continent and is mostly composed of granite rocks. The layer below SLAL is called SIMA. This layer is made of silica and manganese. It isa layer of basaltic rocks which are ‘denser and underlies the continental block to form the ocean floor.

The Mantle (Mesosphere)

This is the layer below the crust. It is composed of iron and manganese. It lies between the crust and the core, The layer which separates erust and mantle is called Mohorovie discontinuity, The mantle is made up of very dense and hot igneous rocks, found in semi liquid states. It extends downwards 2900 km and the temperature ranges between 5000°C and 7000°C. The density of the mantle is 3 3.3 g/cm}. It is divided into two paris namely, the upper and lower mantle. The

upper mantle is rigid and combines with the crust to form @ layer called lithosphere. Below the upper mantle there isa layer called asthenosphere

The Core (Barysphere)

This is the innermost layer of the earth. It is composed of nickel and iron Its diameter is approximately 2500 ~ 2700 km and its temperature is around $S00°C. The average density of the harysphere is about $2 giem3. Most geographers believe that the core is divided into solid and liquid core. The total mass of the earth is about 5.976 x 1021 tonnes ‘Hydrosphere (

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Structure of the Earth

Structure ofthe Earth

The Variation in Density and Thickness of the Concentric Zones of The

Earth's Crust

ROCKS

A rock is an aggregate of mineral particles found in soft, solid or unconsolidated state. The minerale are formed froin one of more of eight main elements. These ar: oxygen, siticon, Rocks can be broadly categorized into three types. These are igneous racks, sedimentary rocks and metamorphic rocks, These kinds of rocks are classified according to their origin, chemical composition and age ‘The Characteristics of The Earth's Crust, The Mantle and The Core

Describe the characterisiics of the earth's crust, he mantle and the core Variations in characteristics ofthe three interior zones of the earth are the result of temperature and pressure as they increases from the surface to the center of the earth Factors which ecounts for such variations ineludes: pressure on the underlying materials, weight of the underlying materials, radioactivity, magma movement and heat generated during the formation ofthe earth.

Types of Rocks of the Earth's Crust

The Types of Rocks of the Earth's Crust Identify types of rocks ofthe earth's crust Igneous rocks ‘These rocks are formed when molten tock cools and solidifies, All igneous rocks originate inside the earth where they are under great pressure, Igneous rocks do not occur in layers and they don't contain fossils which are the chemically-changed remains of ancient plants and animals embedded in rocks, These rocks solidify either within the earth's erust and form intrusive

features or outside the earth's surface and firm extrusive features Igneous rocks are formed when the molten magma is foreed out from the upper mantle to the carth's surface, where it codls and solidifies due to Tow temperature. Crystals form on cooling and the rocks are called erystalline rocks ‘There are two main types of igneous rocks:

• Platonic: these haye solidified deep in the crust and they are seen on the surface only

afler being exposed by prolonged erosion. 2, Voleanie: these have been poured on the earth's surface where they are called lavas. Characteristies of igneous rocks © Igneous rocks reflect Tight 4 -Theyare von seein pers ey moe comin Tose: They are ceynlie rocks, +» Thny.are formed trough cooling and solidification of magma, Tiny ar tne und Wooing pocoaen

• They contain different minerals like iron, magnesium etc

Ny jgneis rcks are found in oma, ring id i the shoves of Lake Vidtid (Mewansa), "he fk ehamipley are rari gabbro, ball and dvi, Sve afoul i Kiliaajar ad Rae (Mey) sch basa, prise are, gabbo, syenite ed pcidoie fk =—— ea -* —_— a af .

tw” Es, «pt a es , > Pe vn ae yy oe Sr “ « gam >» ; aS hy nt ¥ j 5p ae Granite Basalt rocks Sedimentary rocks Sedimentary rocks are found in layers; they contain fossils and are very soft. These are weathered particles formed through deposition and lithfication processes. Sedimentary rocks are formed when the sediments are accumulated, compacted and cemented together. The sedimenis are compacted by compression to form sedimentary rocks. These are called stratified rocks.

Characteristies of sedimentary rocks

• They are formed when particles or sediments are aceumulated, compacted and cemented

together.

• They contain fossils.
• They are found in layers (stata).
• They do not reflect light.
• Theyare non-crystalline rocks,
• They can undergo metamorphic process

Types of sedimentary rocks

Mechanically-formed sedimentary rocks ‘These are formed through weathering process. When weathering agents erode and deposit rock particles, they are accumulated, compacted and cemented together to form sedimentary rocks.

Examples of mechanically formed sedimentary rocks are clays, gravels and alluviums (all

deposited by water), moraines, boulder clay and gravels (deposited by ice) and loess (deposited by wind), sandstones and shale, Sandstone Shale: Shale occurs ina wide range of colours that include. red, brown, green, grey, and black Chemically-formed sedimentary rocks ‘These are formed through chemical precipitation process. They include carbonate (as it is in stalactite and stalagmite), sulphate, chloride, ete. ‘The main examples are gypsum, rock salt,

lignite, dolomite, flint, borax, limonite, haematite, ee Phy oe a Dolomite ‘Sisco tae oammentnes 88 ‘hose are finned tncigh minal proves of decaying aid dosvapotiion Gt aa organisms such as animals and plants. The remains of living organisms are accumulated, cotacied nd cemented tgetiet ts fom eb sdimehey rocks, The an eaples ae Ba (limestone) and coral (formed from animals), and peat, coal and lignite (formed from plants).

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• They are very hard due to prolonged action of heat and pressure.
• Any type of rocks can be subjected to metamorphic rocks.

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• Granite to eis,

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ROCK CYCLE

This isthe cyele in which rocks tend to change from one type to another. For instance igneous rocks may change 1a metamorphic rocks or sedimentary rocks; sedimentary rocks w metamorphic or igneous rocks, ete. It isa relationship in which rocks tend to change from one

type of rock to another.

Necessary conditions for rock eyete to take place 1, First, dhe molten rocks erupt from the interior of the earth and then cool and solidify 10 form igncous rocks. 2 Secondly, the igneous rocks are subjected to denudation process fo form sedimentary rocks

• Third, ether igneous or sedimentary rocks undergo metamorphism, due to profonged heat

and pressure, to form metamogphie rocks

• Fourth, metamorphic or igneous rocks can undergo weathering process through erosion

and transportation of sediments which are further deposited in layers in the ocean or lake floors where they are cemented and consolidated to form sedimentary rocks and vice versa

• Fifth, metamorphic or sedimentary rocks can be subjected to heat and pressure where

melting take place and later cooling, due to low temperature, to form igneous rocks. Years in snillions before Man and Era Period present ‘Major geological events in Africa animals Glaciation of East Attica mountains Formation of Cenozoic Quaternary 1 nver terraces and raised beaches, Age of man

Formation of the Alas mountains, Lava flows ia Age of

Tertiary 162 Ethiopia ‘mammals. Deposition ofimarine sediments in the Sahara and Mesozoic Cretaceous Bs Southern Nigeria. Formation of Enugu coalfield Age olteptiles Break-up of Gondwanaland and Manne invasion of East Aftica coastlands and separation of Malagasy Jurassic 180 Island from mainland Drakensburg lavas and formation of upper Karro Triassic 230 beds. Voleante activity in West Africa

Formation of lower Katro beds, Formation of rich

coal deposits in Tanzania and South Alica tee age Age of Paleozoie Permian 280 in cenral and South Aiea, amphibians Carbonifereus MS (Cape fold formed, Marine invasion of Libya, the Sahara and Western Devonian wos ‘Sudan. Continental basins formed by crustal waeping iris 12s and South Africa, followed by intensive folding sandstones in Guinea, Maly, Voka basin and Nonh Age of marine Marine invasion of Wester Sohara and Kalahari

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Lithification Simplified geological time scale ‘The geological time scale is chart for dating the history of the earth including rock span. It tries to explain the age of rocks as far back as 600 million years ago ‘The simplified geological time scale The Mode of Formation for each Type of Rocks and their Economic Importance Explain the mode of formation for each type of rocks and their economic imporiance ‘The importance of rocks

• Rocks are very important in the formation of soils which can be used for agricultural

production 2 Rocks are used for building purposes: some rocks such as limestone, sandstone, gravels and sand are used for building houses, construction of roads, ete

• Some rocks are used as sources of energy or fuel such as coal and petroleum (mineral

oil). 4, Limestone is widely used for cement manufacturing, In Tanzania, cement is produced at

Tanga, Mbeya and Wazo Hill

5, Salt extraction: salt usually originate from rock accruing strata, for instance, in Tunisia and Morocco there are large deposits of salt.

• Manufacture of chemicals: some rocks contain nitrate or phosphate, while others have

potash. This kind of rocks can be used for making dyes, fertilizers and medicines.

• Mineral deposits: mineral ores occur in veins of some rocks such as igneous rocks. The

minerals are formed when the magma coos down. Valuable minerals extracted from rocks include gold, lead, tin, silver, diamond, copper, zinc, aluminium, calcium and manganese 8 Some rocks are so impressive such that they attract tourist to come and view them. In so doing, the country earns a lot of foreign exchange,

• Some rocks are used for decoration of houses as omaments or they are grinded to

produce powder which is used for decoration,

Simplified Geological Time Scale

The Geological Time Scale

Describe the geological time sale The geological time scale(GTS) is a system of chronological measurement that relates stratigraphy to time, and is used by geologists.palcontologists, and otherEarth scientists to describe the timing and relationships between events that have occurred throughout Earth's history