In geology, a key bed (syn marker bed) is a relatively thin layer of sedimentary
rock that is readily recognized on the basis of either its distinct
physical characteristics or fossil content and can be mapped over a very
large geographic area.[1]
As a result, a key bed is useful for correlating sequences of
sedimentary rocks over a large area. Typically, key beds were created as
the result of either instantaneous events or (geologically speaking)
very short episodes of the widespread deposition of a specific types of sediment. As the result, key beds often can be used for both mapping and correlating sedimentary rocks and dating them. Volcanic ash beds ( and bentonite beds) and impact spherule beds, and specific megaturbidites
are types of key beds created by instantaneous events. The widespread
accumulation of distinctive sediments over a geologically short period
of time have created key beds in the form of peat beds, coal beds, shell beds, marine bands, black in cyclothems, and oil shales. A well-known example of a key bed is the global layer of iridium-rich impact ejecta that marks the Cretaceous–Paleogene boundary (K–T boundary). Please let me know if it works.
They work like a lock and key. Each enzyme is designed to fit into a specific substrate. Well let me start by explaining what an enzyme is and then a subtrate. An enzyme is a protein that speeds up the chemical reaction in a living organism. An enzyme acts as a catalyst for specific chemical reactions, converting a specific set of reactants called substrates into specific products.
The skin has only 2 layers—epidermis and dermis. Hypodermis, if that’s what you have in mind as the third, isn’t considered part of the skin.
The epidermis is a barrier to infection, trauma, and water loss (dehydration); it’s important to our social interactions; and it’s the body’s largest sense organ. The dermis provides toughness and resistance to mechanical stress; provides blood vessels that come close to the epidermis and nourish it (but don’t enter it); contains a variety of sensory receptors for touch, heat, cold, pressure, and vibration; and is an arena of immune defense in which white blood cells can rally at a site of infection and fight off intruders.
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Judith Mcqueen
, former Theatre Tech at Manchester Royal Infirmary (1986-1990)
Answered Jan 16,
