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  2. Stratum - Wikipedia

    en.wikipedia.org/wiki/Stratum

    In the study of rock and sediment strata, geologists have recognized a number of different types of strata, including bed, flow, band, and key bed. [1] [5] A bed is a single stratum that is lithologically distinguishable from other layers above and below it. In the classification hierarchy of sedimentary lithostratigraphic units, a bed is the ...

  3. Social stratification - Wikipedia

    en.wikipedia.org/wiki/Social_stratification

    [2] [3] [4] In modern Western societies, social stratification is defined in terms of three social classes: an upper class, a middle class, and a lower class; in turn, each class can be subdivided into an upper-stratum, a middle-stratum, and a lower stratum. [5]

  4. Lithostratigraphy - Wikipedia

    en.wikipedia.org/wiki/Lithostratigraphy

    Strata in Salta . Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneous or sedimentary relating to how the rock was formed.

  5. Social class - Wikipedia

    en.wikipedia.org/wiki/Social_class

    In a class society, at least implicitly, people are divided into distinct social strata, commonly referred to as social classes or castes. The nature of class society is a matter of sociological research. [26] [27] [28] Class societies exist all over the globe in both industrialized and developing nations. [29]

  6. Stratified sampling - Wikipedia

    en.wikipedia.org/wiki/Stratified_sampling

    Proportionate allocation uses a sampling fraction in each of the strata that are proportional to that of the total population. For instance, if the population consists of n total individuals, m of which are male and f female (and where m + f = n), then the relative size of the two samples (x 1 = m/n males, x 2 = f/n females) should reflect this proportion.

  7. Stage (stratigraphy) - Wikipedia

    en.wikipedia.org/wiki/Stage_(stratigraphy)

    In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition.A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.

  8. Epidermis - Wikipedia

    en.wikipedia.org/wiki/Epidermis

    The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. [1] The epidermis layer provides a barrier to infection from environmental pathogens [2] and regulates the amount of water released from the body into the atmosphere through transepidermal water loss.

  9. Social status - Wikipedia

    en.wikipedia.org/wiki/Social_status

    Social status is the relative level of social value a person is considered to possess. [1] [2] Such social value includes respect, honor, assumed competence, and deference. [3]