39: (Case Study) Quaternary Quandaries - defining the geologic "now" and explorations of the Anthropocene
- Page ID
- 22709
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At the end of this chapter, students should be able to:
- Describe how geoscientists define start and end dates for periods on the geologic time scale.
- Differentiate between the different epochs and ages within the Quaternary Period.
- Differentiate between the different ages within the Holocene Epoch.
- Describe how recent changes to the Holocene were made.
- Discuss the significance of the Meghalayan Age and its associated GSSP.
- Explain the current debate and discussions surrounding the potential defining of a new Anthropocene Epoch.
- Identify what a GSSP, or “Golden Spike” is in the geologic record.
How do we define the time in which we live? Can it be done in a word or an idea? Or, is it through the sum of our material past, the objects we leave behind to tell our story? Do we get to define our time, or is it something left to those who follow us later on?
The band of time can be modeled metaphorically using the old AM/FM radios you may have seen a car, the kind with knobs you can use to tune it. Radio tuners have a starting frequency and ending frequency which, in the case of the FM band, runs from 87.5 to 108 MHz. If you wish to find a particular station, or frequency, all you needed to do was turn the dial. Each frequency was already defined, depending upon your location, by a given radio station. If you wanted the rock station, you tuned it to perhaps 100.7 MHz, and so on. Because it was already there and defined before you used it, you knew what to expect and what the parameters of a particular location on that radio dial was like. Radio stations are not really boundaries in the FM spectrum, but metaphorically they can be viewed as little waystations, locations of significance, amidst the staticky stuff in between, with nothing of distinction to set it apart from any other position on the spectrum.
Geologic time is very similar. How can we use it to give some kind of meaning to the expanse of time?
The Geologic Time Scale is a model that has been developed by lots of people working over lots of time. Their work that helps us answer these difficult questions. As is the case with all models, the Geologic Time Scale is wrong in many ways. However, it is still very useful. As time and knowledge accumulate, we improve the model. Such improvements can include everything from simple date changes to larger-scale changes like the introduction of new periods or epochs. However change progresses, the time scale is a model that represents our best understanding of the band expanse of time as we understand it. The geologic time scale is not static, but dynamic. It is managed by the International Commission on Stratigraphy (ICS), an affiliate of the International Geological Union. The work of the ICS is to compile ongoing research into the various portions of the time scale in order to refine the boundaries of the Eons, Eras, Periods, and Epochs we use to define time. To do this, Global Stratotype Sections and Points (GSSPs) are identified that provide a consensus marker in time for any given boundary. These GSSPs are often referred to as “Golden Spikes”, a reference to the golden spike used to complete the Trans-Continental Railroad, as they serve as clearly-defined time markers that allow researchers (and professors and students!) to share in common discussion.
But, how hard is it exactly to define such boundaries in time?
Over the course of this case study, we will explore three critical questions:
1. How do we use the geologic time scale as a model to make sense of time?
2. How do we make changes to this model as we learn more about time?
3. Can we use this model to help us define our own time in the present and recent past?
The geoscientists working with the Subcommission on Quaternary Geology are wrestling with these questions. Their subcommission is a part of the International Commission on Stratigraphy (ICS). Ultimately, this case study will explore a proposed new epoch, the Anthropocene Epoch. Before we get there, we need to spend some time exploring how the ICS has gone about defining our most recent era, periods, epochs, and ages. Hopefully, we can then revisit the above questions and have some satisfying answers.