We know that the Earth shaped like a ball. If we continue digging at a particular place, we would notice that the temperature goes on increasing with the increase in depth. There are three main layers of Earth — the top, second and third. The top or first layer of Earth is a thin crust of hard rocks that floats on the second thicker layer of rock called ‘mantle’. This is so hot that most of its rocks are partly molten. The third layer is made of hot liquid iron. In fact, at the core it is extremely hot. The temperature can be imagined from the huge amount of energy, which is released when the volcanoes erupt. Around the year 1800, some Italian scientists performed certain experiments to make use of Earth’s internal heat. They dug a hole in the Earth through which jets of hot steam and pungent gases shot out. These blow-holes are a sign of volcanic activity taking place under the ground. The gases they release into the air came from molten rocks known as magma, which lies at depths ranging between 20,000 and 80,000 metres or more. Scientists also found boric acid in these vents. An industry was set up to extract this chemical substance in Italy in 1818. Later, it was discovered that the power of these gas jets could be harnessed for other tasks, including the generation of electricity. For the first time geothermal electricity was generated at Landarello in Italy, in 1904. The internal heat can be used to produce electric power in four ways: dry steam, as at Landarello; hot water as at Reykjavik, in Iceland; low temperature areas in basins of sedimentary rocks, containing water between 40°C and 100°C which is used for agricultural purposes such as, heating glass houses and high pressure zones found by petroleum drilling deep in sedimentary basins. The natural gas released from the Earth in particular localities (generally near deposits of mineral oil) is used as fuel and also as a source of energy. In the last few years, the scientists have developed several mechanisms for the optimum use of Earth’s internal heat. They have been trying to develop such instruments that could be used to utilise the Earth’s geothermal energy effectively.