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When William Smith and Sir Charles Lyell first recognized that rock strata represented successive time periods, there was no way to determine what time scale they represented. The age of the Earth and of the rock strata was the subject of scientific debate for over 100 years as various advances in other sciences continued to place the creation of the Earth further into the past. In the latter part of the 20th century, it became possible to assign relatively firm dates using radioactive dating. In the intervening century and a half, geologists and paleontologists devised two relative time scales. One scale -- termed the Geologic Timescale -- is used by both sciences. Geologists tend to talk in terms of Upper/Late, Lower/Middle and often Middle parts of periods or eras -- e.g. "Upper Jurassic", "Middle Cambrian". Paleontologists divide the same periods into sometimes regional faunal assemblages. For example, in North America the Late Neoproterozoic and Early Cambrian are grouped into a Waucoban series that is then subdivided into zones based on trilobites. The same Neoproterozoic timespan is split into Tommotian , Atdabanian and Botomian periods in East AsiaEast Asia is a subregion of Asia. It covers about 6,640,000 km², or 15 percent of the continent. The following countries are located in East Asia: China, except for the province of Qinghai and the autonomous regions of Xinjiang and Tibet, which may also b and SiberiaSiberia ( Russian: , common English transliterations: Sibir Sibir' is a vast region of Russia and northern Kazakhstan, constituting all of northern Asia, and extending eastward from the Ural Mountains to the Pacific Ocean, and southward from the Arctic Oc.

In 1977 The Global Commission on Stratigraphy started an effort to define global references ( GSSPGSSP stands for Global Stratigraphic Section and Point . GSSPs are internationally agreed to reference stratigraphic sections representing the boundaries for paleontologic faunal stages. Since faunal stages do not cross geologic period boundaries, a subses) for geologic periods and faunal stages.