Link to article: https://www.researchgate.net/publication/273467448_Defining_the

Question

Link to article: https://www.researchgate.net/publication/273467448_Defining_the_Anthropocene

Possible Short Answer Question 5: (15 points total) Make a case for whether humans are geologic agents A) To define a new geologic time unit, there are strict criteria that must be met. Those criteria depend on whether the event is marked by a GSSP or a GSSA. Define what each acronym means, and outline the criteria for each. Make sure to explicitly note how the criteria differ Finally, provide an example of a geologic time unit boundary that is marked by a GSSP making sure to explicitly outline how the various criteria are met. (8 points)

Explanation / Answer

As the paper outlines, defining an era or a new geologic time unit requires the location of a global marker of an event in rock, sediment, glacier ice, or other stratigraphic material, which is referred to as a Global Stratotype Section and Point (GSSP), plus other auxiliary stratigraphic markers indicating changes to the Earth system. Alternatively, a date can be agreed by committee, after a survey of the stratigraphic evidence, known as a Global Standard Stratigraphic Age (GSSA).

The criteria for defining a GSSP, as described by Remané et al. (1996) is by placing a ‘golden spike’ at the event, marking the unique place where a specified point in time is indicated. Sections elsewhere are then correlated with this using all possible methods. Hence, the GSSP must be at a level and locality that has maximum possible applicability for global correlation – though in practice no single GSSP is likely to be directly correlatable over the whole world, so that supplementary reference points may be necessary.

A geologic section has to fulfill these specific criteria to be adapted as a GSSP, by the International Commission on Stratigraphy (ICS):

As far as GSSA is concerned, a worldwide multidisciplinary effort has been ongoing since 1974 to define the important metrics. The points and strata need be widespread and contain an identifiable sequence of layers or other unambiguous markers (identifiable or quantifiable) attributes. GSSAs are nothing but generally more recent and preferred markers used primarily for time dating of rock layers older than 630 million years ago, lacking a good fossil record.  The ICS committee attempts to meet the criteria for the GSSPs first and if those fail, and enough information is available then preliminary selection of several competing GSSA prospects or proposals is made.  GSSAs are basically defined based on fixed dates and selected criteria.

An example of a geological time scale unit boundary marked by GSSP is the 11,700 calendar yr b2 k for the base of the Holocene, with a maximum counting error of 99 yr. The GSSP for this is the Greenland ice core from NorthGRIP (NGRIP), as ratified in 2008. The primary marker criteria were Climatic -- End of the Younger Dryas cold spell, which is reflected in a shift in deuterium excess values. The GSSP, NGRIP contains a proxy climate record across the Pleistocene–Holocene boundary of unprecedented clarity and resolution. Many of the requirements of a GSSP, such as a sufficiently rapid rate of sedimentation, the assured continuity of sedimentation and a permanently fixed marker, are met in this GSSP.

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