Make a case for whether humans are geologic agents. A) To define a new geologic

Question

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) B) Choose one of the five possible 'golden spikes' mentioned in the article Defining the Anthropocene. Present an argument for why it should or should not mark the beginning of the Anthropocene. Your argument must include the following: 1. Discuss what the potential golden spike marks and what this event looks like in the geologic record. 2. Discuss how this event fulfills (or fail to fulfil) the criteria for the beginning of a new geologic time unit. You can go with either the GSSA or GSSP criteria - just make sure you are supporting your argument! (note: you do NOT have to choose one of the spike that the authors argue is a potential beginning of the Anthropocene - be creative but make sure you are relying on evidence!) 7 points)

Explanation / Answer

A. GSSP stands for Global Boundary Stratotype Section and Point. It defines the lower boundary of a stage on the geologic time scale. The following set of criteria falls under GSSP :

i. GSSP has to define the lower booundary of a geologic stage.

ii. The lower boundary should be marked by a primary and secondary marker.

iii. Radiometrically dated minerals should present in the marker horizons.

iv. The marker should be independent of facies.

v. Sedimentation should be continuous with one type of facies only.

vi. The outcrop should have adequate thicknes.

vii. The outcrop should not be effected by tectonism or metamorphism.

Example - Base of Ediacaran period marked by GSSP.

GSSA stans for Global Standard Stratigraphic Age. GSSA is used to define the boundaries between deifferent geological periods, epochs or ages on the overall geological time scale. It is a chronological reference point.

The criteria for GSSA are as follows :

i. There should be identifiable sequence of layers or markers.

ii. Used for rocks older than 630 million years ago lacking a good fossil record.

Example - The boundary between Proterozoic and Archean period.

The differences between GSSP and GSSA are

i. GSSPs are mainly based on palaeontological criteria whereas GSSA does not need fossil records.

ii. GSSPs are based on important events and transitions within a particular section whereas GSSA defines the boundary between periods,epochs or ages on overall geological time scale. GSSA is based on fixed date and selected criteria.

B. GSSP is also known as 'golden spike', is the preffered boundary marker. This marks the beginning of most recent geologic age i.e. antropocene. There are some arguments over this. These include

1. Not relying on solid aggregate mineral deposits for the boundary.

2. The boundary is completely lacking fossils.

3. How to formalize a time unit that extends to the present.

For these a single dated level within a sinle stratigraphic record was required to be chosen as GSSP primary marker.

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