Ignition timing Ignition timing In a spark ignition internal combustion engine, Ignition timing refers to the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke. The need for advancing (or retarding) the timing of the spark is because fuel does not completely burn the instant the spark fires, the combustion gases take a period of time to expand and the angular or rotational speed of the engine can lengthen or shorten the time frame in which the burning and expansion should occur. In a
Archaic humans In this case the standard taxonomy is used, i.e. "Homo rhodesiensis", or "Homo neanderthalensis". The evolutionary dividing lines that separate modern humans from archaic humans and archaic humans from "Homo erectus" are unclear. The earliest known fossils of anatomically modern humans such as the Omo remains from 195,000 years ago, "Homo sapiens idaltu" from 160,000 years ago, and Qafzeh remains from 90,000 years ago are recognizably modern humans. However, these early modern humans do possess a number of archaic traits, such as moderate, but not prominent, brow ridges. The emergence of archaic humans is sometimes used as an example of