quaternary

1. Consisting of four; in fours.
2. Quaternary Of or belonging to the geologic time, system of rocks, or sedimentary deposits of the second period of the Cenozoic Era, from the end of the Tertiary Period through the present, characterized by the appearance and development of humans and including the Pleistocene and Holocene epochs.
3. Chemistry. Relating to an atom bonded to four carbon atoms: a quarternary nitrogen atom.

1. The number four.
2. The member of a group that is fourth in order.
3. Quaternary The Quaternary Period or its system of deposits.

[Latin quaternārius, from quaternī, by fours, from quater, four times.]

A period that encompasses at least the last 3,000,000 years of the Cenozoic Era, and is concerned with major worldwide glaciations and their effect on land and sea, on worldwide climate, and on the plants and animals that lived then. The Quaternary is divided into the Pleistocene Epoch and Holocene. The universal term Pleistocene is gradually re-placing Quaternary; Holocene involves the last 7000 years since the Pleistocene. See also Cenozoic; Glacial epoch; Holocene; Pleistocene.

Having four elements. Widely used in medicine, quaternary ammonium salts are molecules containing four alkyl or aryl groups attached to a nitrogen atom.

geology Although etymologically meaning of four parts, the quaternary in the geochronologic scale is the fourth part in sequence of what was originally the Cambrian period. It began 1.5 million years ago and is still continuing; hence it can be taken to mean the current time (its second epoch, the Holocene, being the latest 11 000 years).

The most recent period of the Cenozoic era. During the Pleistocene epoch of this time, from about 1.8 million years bp, to some 10 000 years ago, much of Britain's glacial and periglacial scenery evolved.

1. fourth in a series.
2. made up of four elements or groups.

• q. ammonium compounds — synthetic cationic detergents commonly used as disinfectants. They act against cell wall lipids in bacteria. An example is benzalkonium chloride. Effective in teat dips for mastitis control. Called also QUATs.
• q. structure — the arrangement of separate polypeptide subunits in the structure of a multimeric protein.