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Rice provides more food for more people than any other cereal crops in the world. Its is
The basic food crop in much of southern and eastern Asia.
Rice needs hot weather and plenty of water. The water may come from heavy rain, such as the monsoon rains of Asia, or from irrigation. Rice needs flat land, because the water level in the fields must be carefully controlled. Many hillsides in Asia are terraced to get
Enough flat land.
On the edges of some of the Earths Natural deserts, the environment is being upset by poor farming methods and mismanagement.
Semi – Desert areas have fragile soils and difficult climates.Several good years are often followed by several bad years. In the good years, farmers may extend the cultivated areas, or increase their flocks and herds and dig more wells . But ina series of dry years,
Crops fail, animals exhaust the pasture , the bare soil is roded and many wells dry up. Such problems created the dust bowl in the USA in the 1930 and extended the Sahara in the 1970s.
Artesian water is underground water which rises to the surface under natural pressure.The name comes from Artois in France, where many wells have been dug to reach artesian water in the underlying chalk.
Rain falling o higher land can flow through the layers of porous rocks. Beneath the low land, the porous rocks are sandwiched between impervious layers. The water bearing layer is called an aquifer .The Great Artesian Basin Of Australia is the worlds largest.
The majority of minerals found in the rocks of the Earth’s Crust are silicates.
The Earth’s crust is made up of different kind of rocks. Most sedimentary rocks from accumulations of minerals which were weathered out of igneous rocks. Most of these minerals will be silicates.Silicates are a large group of minerals , all of which contains silica and oxygen. The commonest silicate family is feldspar.
Coal is a rock which is burned as fuel. It is called a ‘fossil fuel’ because it formed from the remain of trees and plants millions of years ago. Imprints of these plants can be found on some lumps of coal.
Coal is usually found in layers, called seams, of different thickness sandwiched between other rocks which formed at the same time. The oldest known coal seams are about 360 million years old .
Oil and natural gas are fossil fuels. They formed from the remains of tiny plants and animals which one lived in tropical seas. They were changed by chemical processes into gases and liquids.
Oil and gas collect in porous rocks, which allow liquids to soak through. They are trapped between impervious rocks, which will not allow liquids to pas through. Some oil wells pump oil froma huge area, but other tap only a small area and soon run dry.
Monument Valley is part of the Colorado Plateau, in the dry south – west of the USA.
The towers , columns and castle – like masses of rock shown in the photograph are completely natural monuments. They are mainly sandstones and other sedimentary rocks
