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One can produce a tar-like substance from corn stalks by heating them in a microwave oven. This process is known as pyrolysis. Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. [1]
Earth was discovered to have a solid inner core distinct from its molten Earth's outer core in 1936, by the Danish seismologist Inge Lehmann's [7] [8] study of seismograms from earthquakes in New Zealand, detected by sensitive seismographs on the Earth's surface. She deduced that the seismic waves reflect off the boundary of the inner core and ...
The heating (dry distilling) of wood causes tar and pitch to drip away from the wood and leave behind charcoal. Birchbark is used to make birch-tar, a particularly fine tar. The terms tar and pitch are often used interchangeably. However, pitch is considered more solid, while tar is more liquid.
The average magnetic field strength in Earth's outer core is estimated to be 2.5 millitesla, 50 times stronger than the magnetic field at the surface. [9] [10] As Earth's core cools, the liquid at the inner core boundary freezes, causing the solid inner core to grow at the expense of the outer core, at an estimated rate of 1 mm per year.
Earth's mantle is a layer of silicate rock between the crust and the outer core. It has a mass of 4.01 × 10 24 kg (8.84 × 10 24 lb) and makes up 67% of the mass of Earth. [ 1 ] It has a thickness of 2,900 kilometers (1,800 mi) [ 1 ] making up about 46% of Earth's radius and 84% of Earth's volume.
Earth cutaway from core to exosphere Geothermal drill machine in Wisconsin, USA. Temperature within Earth increases with depth. Highly viscous or partially molten rock at temperatures between 650 and 1,200 °C (1,200 and 2,200 °F) are found at the margins of tectonic plates, increasing the geothermal gradient in the vicinity, but only the outer core is postulated to exist in a molten or fluid ...
It was later postulated that hotspots are fed by streams of hot mantle rising from the Earth's core–mantle boundary in a structure called a mantle plume. [6] Whether or not such mantle plumes exist has been the subject of a major controversy in Earth science, [ 4 ] [ 7 ] but seismic images consistent with evolving theory now exist.
The respective mean heat flows of continental and oceanic crust are 70.9 and 105.4 mW/m 2. [1] While the total internal Earth heat flow to the surface is well constrained, the relative contribution of the two main sources of Earth's heat, radiogenic and primordial heat, are highly uncertain because their direct measurement is difficult.