The "Golden Nail" is actually a colloquial term for the Global Boundary Stratigraphic Sections and Sites (GSSP) of global chronostratigraphic units. It is a typical or standard boundary of chronostratigraphic units designated by the International Union of Geological Sciences and the International Commission on Stratigraphy. The "Golden Nail" marked at a specific location and in a specific rock sequence is a "scale" of geological history, and it is the only marker for determining and identifying the boundary between two global geological epochs.
The "stage" is the basic stratigraphic unit in the global chronostratigraphic table. To establish a globally unified chronostratigraphic table, it is necessary to establish global standards for each stage, so as to understand, interpret, analyze, and study various geological bodies (rocks, strata, etc.) and geological events formed in different regions of the world at the same time according to a unified time (era) scale. This is just like having a scale on a clock, so that we can use a unified language to say "what time it is".
For a particular "stage", there is only one "Golden Nail" worldwide as a standard or model. The selection of each "Golden Nail" must involve a global survey of the strata of this era and the organization of international authoritative experts to conduct detailed research, verification, and discussion on the candidates of the proposed "Golden Nail" sections and related research results. Then, the experts from various stratigraphic commissions under the International Commission on Stratigraphy vote to approve and announce them. The "Golden Nail" is recognized by scientists worldwide as a standard for the division and comparison of a specific geological era globally. Therefore, its successful acquisition often signifies that a country's geological research results in this field have reached world-leading levels, and its value is self-evident.