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 Most common words in Spanish Below are two estimates of the most common words in Modern Spanish. Each estimate comes from an analysis of a different text corpus. A "text corpus" is a large collection of samples of written and/or spoken language, that has been carefully prepared for linguistic analysis. To determine which words are the most common, researchers create a database of all the words found in the corpus, and categorise them based on the context in which they are used. The first table lists the 100 most common word forms from the Corpus de Referencia del Español Actual