calcium
Etymology
Coined by British chemist Humphry Davy in 1808, from Latin calx (“lime, limestone”) because it occurs in limestone.
noun
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The chemical element (Symbol Ca), with an atomic number 20. It is a soft, silvery-white alkaline earth metal which occurs naturally as carbonate in limestone and as silicate in many rocks. Oxygen levels on Earth skyrocketed 2.4 billion years ago, when cyanobacteria evolved photosynthesis:[…]. The evolutionary precursor of photosynthesis is still under debate, and a new study sheds light. The critical component of the photosynthetic system is the “water-oxidizing complex”, made up of manganese atoms and a calcium atom. 2013 September-October, Katie L. Burke, “In the News”, in American Scientist -
(countable) An atom of this element.
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