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  2. List of tectonic plates - Wikipedia

    en.wikipedia.org/wiki/List_of_tectonic_plates

    This is a list of tectonic plates on Earth's surface. Tectonic plates are pieces of Earth's crust and uppermost mantle, together referred to as the lithosphere. The plates are around 100 km (62 mi) thick and consist of two principal types of material: oceanic crust (also called sima from silicon and magnesium) and continental crust (sial from ...

  3. List of numeral systems - Wikipedia

    en.wikipedia.org/wiki/List_of_numeral_systems

    "A base is a natural number B whose powers (B multiplied by itself some number of times) are specially designated within a numerical system." [1]: 38 The term is not equivalent to radix, as it applies to all numerical notation systems (not just positional ones with a radix) and most systems of spoken numbers. [1]

  4. Plate tectonics - Wikipedia

    en.wikipedia.org/wiki/Plate_tectonics

    Plate tectonics (from Latin tectonicus, from Ancient Greek τεκτονικός (tektonikós) 'pertaining to building') [ 1] is the scientific theory that Earth 's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. [ 2][ 3][ 4] The model builds on the concept of continental ...

  5. Babylonian cuneiform numerals - Wikipedia

    en.wikipedia.org/wiki/Babylonian_cuneiform_numerals

    The Babylonian system is credited as being the first known positional numeral system, in which the value of a particular digit depends both on the digit itself and its position within the number. This was an extremely important development because non-place-value systems require unique symbols to represent each power of a base (ten, one hundred ...

  6. History of ancient numeral systems - Wikipedia

    en.wikipedia.org/wiki/History_of_ancient_numeral...

    Numeral systems. Number systems have progressed from the use of fingers and tally marks, perhaps more than 40,000 years ago, to the use of sets of glyphs able to represent any conceivable number efficiently. The earliest known unambiguous notations for numbers emerged in Mesopotamia about 5000 or 6000 years ago.

  7. Earth's crust - Wikipedia

    en.wikipedia.org/wiki/Earth's_crust

    Earth's crust is its thick outer shell of rock, referring to less than one percent of the planet's radius and volume. It is the top component of the lithosphere, a solidified division of Earth's layers that includes the crust and the upper part of the mantle. [ 1] The lithosphere is broken into tectonic plates whose motion allows heat to escape ...

  8. List of vacuum tubes - Wikipedia

    en.wikipedia.org/wiki/List_of_vacuum_tubes

    The system was used in 1942–44 and assigned numbers with the base form "1A21", and is therefore also referred to as the "1A21 system". [1] The first numeric character indicated the filament/heater power rating, the second alphabetic character was a code for the function, and the last 2 digits were sequentially assigned, beginning with 21

  9. Outline of plate tectonics - Wikipedia

    en.wikipedia.org/wiki/Outline_of_plate_tectonics

    Plate tectonics (from Latin tectonicus, from Ancient Greek τεκτονικός (tektonikós) 'pertaining to building') is the scientific theory that Earth 's lithosphere comprises a number of large tectonic plates, which have been slowly moving since about 3.4 billion years ago. The model builds on the concept of continental drift, an idea ...