Fossil fuel embedded energy is still photosynthetic in origin. Terrestrial plants, on the other hand, tended to form coal and methane. Many of the coal fields date to the Carboniferous period of Earth's history. Terrestrial plants also form type III kerogen, a source of natural gas. There is a wide range of organic, or hydrocarbon, compounds in any given fuel mixture. The specific mixture of hydrocarbons gives a fuel its characteristic properties, such as boiling point, melting point, density, viscosity, etc. Some fuels like natural gas, for instance, contain only very low boiling, gaseous components. Others such as gasoline or diesel contain
Interlanguage fossilization does motivation to achieve native-like competence diminish? The concept of fossilization in SLA research is so intrinsically related to interlanguage that Selinker considers it to be a fundamental phenomenon of all SLA and not just to adult learners. Fossilization has received such wide recognition that it has been entered in the "Random House Dictionary of the English Language" (1987). Selinker's concept of fossilization is similar to that of Nemser, Tarone, and Sridhar, all of whom attempted to explore the causes of fossilization in second language learners' interlanguage. Fossilization has attracted considerable interest among researchers and has engendered significant differences of