Simplified Geological Time Scale

Simplified Geological Time Scale

The geological time scale is a 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

Era	Period	Years in millions before present	Major geological events in Africa	Man and animals
Cenozoic	Quaternary	1	Glaciation of East Africa mountains. Formation of river terraces and raised beaches.	Age of man
	Tertiary	163	Formation of the Atlas mountains. Lava flows in Ethiopia.	Age of mammals.
Mesozoic	Cretaceous	135	Deposition of marine sediments in the Sahara and Southern Nigeria. Formation of Enugu coalfield.	Age of reptiles
	Jurassic	180	Break-up of Gondwanaland and Marine invasion of East Africa coastlands and separation of Malagasy Island from mainland.
	Triassic	230	Drakensburg lava and formation of upper Karro beds. Volcanic activity in West Africa.
Paleozoic	Permian	280	Formation of lower Karro beds. Formation of rich coal deposits in Tanzania and South Africa. Ice age in central and South Africa.	Age of amphibians
	Carboniferous	345	Cape fold formed.
	Devonian	405	Marine invasion of Libya, the Sahara and Western Sudan. Continental basins formed by crustal warping
	Silurian	425	Continental sedimentation in Zaire basin, Tanzania and South Africa, followed by intensive folding.
	Ordovician	500	Extensive deposition of sediments. Formation of sandstones in Guinea, Mali, Volta basin and North West Ethiopia	Age of marine invertebrates
	Cambrian	600	Marine invasion of Western Sahara and Kalahari basin.
Proterozoic	Pre Cambrian or Archaean		Glaciations of Africa South of Equator. Extensive metamorphism of oldest known fossilized, unicellular algae formed in Swaziland and Mali.	Algae

The Importance of Rocks

1. 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, etc.
3. 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.
6. 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.
7. Mineral deposits: mineral ores occur in veins of some rocks such as igneous rocks.
8. Valuable minerals extracted from rocks include gold, lead, tin, silver, diamond, copper, zinc, aluminum, calcium and manganese.
9. Rocks are so impressive such that they attract tourist to come and view them.
10. Rocks are used for decoration of houses as ornaments or they are grinded to produce powder which is used for decoration.