Welcome to the Anthropocene EarthCache
Hidden : 4/2/2019
Difficulty:
2.5 out of 5
Terrain:
1.5 out of 5

Size: Size: other (other)

Join now to view geocache location details. It's free!

Watch

How Geocaching Works
Looking for a different adventure?

Please note Use of geocaching.com services is subject to the terms and conditions in our disclaimer.

Geocache Description:


This Earthcache is located in the Table Bay Nature Reserve - Rietvlei Section, and is only available between 07h30 and 16h00 daily,

The geologic time scale is a system of chronological dating that relates geological strata to time. It is used to distinguish timing and relationships of events that have occurred during the Earths history. The "clock" illustration below shows some of the major units of geological time together with definitive events. It is noticeable that the roughly two million year period during which recognizable humans have been around, is too small to be visible at this scale!



The geologic time scale is divided firstly by the broadest category called an Eon. The Eons, from oldest to youngest are the Hadean, Archean, Proterozoic and Phanerozoic. The first three are often collectively called the "Precambrian". We are currently living in the Phanerozoic Eon, which means "visible life", and which began 541 million years ago and so represents about 12% of the Earths history.

Eons are subdivided into Eras, the second-longest unit of geological time. Our Phanerozoic eon is made up of three eras - the Paleozoic, Mesozoic and Cenozoic. Note that the Paleozoic marks the arrival of the first vertebrates on Earth (the trilobites) and the origin of land plants, the Mesozoic represents the age of dinosaurs and the Cenozoic marks the arrival of mammals and flowering plants.

Eras are further divided into Periods. The Cenozoic era is made up of the Paleogene, Neogene and Quaternary periods. The most famous period is probably the Jurassic period, the height of the dinosaurs, and which belongs in the Mesozoic era.

Periods of geologic time can be broken down even further, into Epochs, and those of the Quaternary period are the Pleistocene and Holocene epochs.

Here is a diagrammatic representation of geologic time known as the Geological Table:



The above geologic time scale and geological table are the result of hundreds of years of investigation and research, yet they remain very much a work in progress. As it currently stands, these have been accepted for many many years by geologists and anthropologists alike... until now...
There is growing consensus among scientists that humankind is making its mark on this planet, and that a new geologic epoch should be introduced to reflect the effects that we are having. According to the Union of Geological Sciences (the organization in charge of defining Earths timescale), we are officially in the Holocene epoch, which started some 11 700 years ago. However, many experts say this is outdated and are arguing for a new epoch - The Anthropocene.

The word "anthropogenic" means human-influenced, and with all the mass extinctions, pollution, deforestation and alteration of the atmosphere directly caused by man, it seems fitting that a new epoch of this name is introduced. Some interesting examples of these influences, and arguments for the new epoch, are:
(a) human activities have accelerated the rate of species extinction. From 1950 alone, algal biomass in the oceans has decreased by around 40% (probably as a result of ocean warming)
(b) atmospheric carbon dioxide levels over the past million years has been between 180 and 280 ppm. As of 2015/16, atmospheric concentrations are exceeding 400 ppm
(c) humans are affecting biodiversity. The domestic chicken (formerly the red junglefowl which was native only to southeast Asia) is now the worlds most common bird while livestock makes up around 60% of the biomass of all mammals on Earth.
(d) human activities change ecosystems. For example, the entire Black Sea ecosystem has changed in the last 2000 years due to nutrient and silica influx from eroding deforested lands along the Danube River.
(e) the amount of nitrogen and phosphorous in our soils in the past century has doubled with fertiliser us, the largest impact on the nitrogen cycle in the last 2.5 billion years!
(f) there is so much plastic in our waterways and oceans that microplastic particles are now virtually ubiquitous, and plastics will likely leave identifiable fossil records for future generations to discover.
(g) a permanent layer of airborne particulates now exists in sediment and glacial ice - such as black carbon from fossil fuel burning.

So, whilst we are still officially in the Holocene epoch, it may not be long before consensus is reached and the Anthropocene epoch is ushered in! There are still lots of debates to be had, most notably about when would the epoch have begun. There is even an Anthropocene Working Group, which met in Oslo in April 2016, to consolidate evidence supporting the argument for the Anthropocene. They voted to recommend the new epoch, and should this recommendation be approved by the International Commission on Stratigraphy, it would then just require ratification by the Union of Geological Sciences to be formally adopted.



In order to qualify to log this Earthcache, make your way to the Viewpoint reference point and observe the following:

* looking south you will see the iconic Devils Peak, Table Mountain and Lions Head in the distance. The upper parts of these mountains are made of the Table Mountain Group of sedimentary rocks, which were deposited during the Ordovician, Silurian and Devonian periods of the Paleozoic era. Dating the Table Mountain Group is difficult but they are probably around 340 to 510 million years old.

* still looking south, and at the same mountains, the lower parts comprise the Malmesbury Group of rocks, which are even older. The Malmesbury Group, deposited as marine mud sediment, was formed between 560 and 540 million years ago, making these rocks part of the late Proterozoic era.

* So what happened in the 30 million year gap? Well, the Cape Granite Suite, found around the base of Lions Head, down the Atlantic Seaboard and notably in the Paarl region, marks an episode of granitic magma that intruded into the Malmesbury Rocks about 540 million years ago. This was followed by a period of erosion or destruction of crust where materials are removed rather than deposited, resulting in a discontinuity before the deposition of the Table Mountain group of rocks.

* The sandy soils of the entire "Cape Flats" area beyond Table Mountain (not visible from here) as well as the ground you are standing on right now and along this western shoreline, known locally as the Witzand and Strandfontein Formations, were deposited during the Quaternary period, which makes them less than 2.5 million years old.

* The wetland and lake that you see in the foreground, believe it or not, are not entirely natural. The Witzand Formation sands in this region were dredged and mined from the area to provide fill materials that were then utilised in the expansion of Cape Town harbour in the 1970s! This left a large depression which subsequently filled with water and resulted in the lakes you see and can enjoy presently.

Finally, please send your answers to the following questions to the CO by email or using the message board within a reasonable time frame after logging your find:
1. What is the oldest geologic eon?
2. Which era represents the age of dinosaurs?
3. What epoch are we officially currently in?
4. Using what you can see around you from the Viewpoint reference point as evidence, describe at least two ways that man has influenced or affected the surroundings?
5. Describe the Witzand sands as observed in the vicinity of GZ. The best place to examine the sands is in the landscaped areas near the parking coordinates, especially if mole activity has brought the sands up above ground. Why do you think they made a good fill material for the harbour expansions?
6. Although optional, it would be great if you could post a picture of yourself at the Viewpoint reference point.


The following references were used in compiling this Earthcache:
Wikipedia
Anthropocene by Erle Ellis (2013)
The Rocks & Mountains of Cape Town by John Compton (2004)
Digital Atlas of Ancient Life
The Anthropocene Epoch by Damian Carrington (2016)

Additional Hints (Decrypt)

Erzrzore gb fraq lbhe nafjref!

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)


Advertising with Us