Life is composed of many chemical elements,
and these are required in the right amounts, at the right time, and in the
right relative concentrations to each other. If these conditions are not
met, then life is limited, preventing the growth of an individual, population,
or species, or even causing its local extinction. Of the 92 naturally occurring
chemical elements, only 18 have been
shown to be essential elements (Elements
without which plants cannot grow and
complete life cycles). Essential
elements required by plants in relatively large amounts are called
macronutrients (A nutrient is a chemical
species that is actively taken up by an organism and is used to maintain its
bodily function). Macronutrients are: carbon, hydrogen,
oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur. Carbon,
hydrogen and oxygen are taken mostly from air and water and the rest from soil solids.
Those required in smaller amounts are known as micronutrients: iron, manganese,
boron, zinc, copper, chlorine, molybdenum, nickel and cobalt. Sodium and silicon are called quasi essential elements, because they are required for some, but
not for all, plants. Each element plays a special role in organisms. In
addition, chromium, nickel, stannous in trace amounts are essential for
animals. All these together are called
bioelements.
Geologic cycle
The processes
responsible for the formation and change of Earth materials are referred to as
the rock cycle, which is a group of sub cycles: tectonic, rock, hydrologic and biogeochemical cycles.
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