Atmosphere of Earth the border between the atmosphere and outer space. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around . Several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition. The study of Earth's atmosphere and its processes is called atmospheric science (aerology). Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann. The three major constituents of Earth's atmosphere are nitrogen, oxygen, and argon. Water vapor accounts for roughly 0.25% of the atmosphere by mass. The concentration of water vapor (a greenhouse gas) varies significantly from around
Most common words in Spanish (CREA), a text corpus compiled by the Real Academia Española (RAE). The RAE is Spain's official institution for documenting, planning, and standardising the Spanish language. A "word form" is any of the grammatical variations of a word. The second table is a list of 100 most common lemmas found in a text corpus compiled by Mark Davies and other language researchers at Brigham Young University in the United States. A "lemma" is the primary form of a word—the one that would appear in a dictionary. The Spanish infinitive "tener" ("to have") is a lemma, while "tiene" ("has")—which is a conjugation