Mesoamerican calendars was of ritual significance to a number of Mesoamerican cultures. A third major calendar form known as the Long Count is found in the inscriptions of several Mesoamerican cultures, most famously those of the Maya civilization who developed it to its fullest extent during the Classic period (ca. 200–900 CE). The Long Count provided the ability to uniquely identify days over a much longer period of time, by combining a sequence of day-counts or cycles of increasing length, calculated or set from a particular date in the mythical past. Most commonly, five such higher-order cycles in a modified vigesimal (base-20)
Nitrogen fixation Nitrogen fixation Nitrogen fixation is a process by which nitrogen in the Earth's atmosphere is converted into ammonia (NH) or related nitrogenous compounds. Atmospheric nitrogen, which is molecular dinitrogen (N), is relatively nonreactive and is metabolically useless to all but a few microorganisms. The fixation process converts N into ammonia, which is metabolized by most organisms. Nitrogen fixation is essential to life because fixed inorganic nitrogen compounds are required for the biosynthesis of all nitrogen-containing compounds. Therefore, as part of the nitrogen cycle, it is essential for agriculture and the manufacture of fertilizer. It is also, indirectly, relevant to the