Timeline in perspective.
We need to understand how old the earth is to get a feeling for this.
“The Earth is very old indeed. The oldest mineral grains found on Earth so far are over 4 billion years old. Rocks from the moon are even older and it is estimated that the age of the solar system is around 4.6 billion years old.” - The Geological Society of America’s EarthCache Academy
Attempts at calculations.
Various people such as Archbishop James Ussher who did one of the first scientific measurements of the earth’s age (the Hebrew begat theory) more measured man’s time on earth than the age of earth itself.
Other fascinating studies by Edmund Halley (of Comet Halley fame), John Jolly, Phillips, Huxley, Winchell, Wallace & Haughton all calculated between 3 and 1526 million years!
Current estimates are around 4540 million years, a baby compared to the estimations of the Universe’s age – 13.8 billion years.
That’s a lot of water under the bridge!!! Literally!
This Earthcache.
Each one of these layers would have taken hundreds of thousands of years to form.
What we see here are layers of sedimentary rock where the blasters have blasted open to build the Ollie Deneyschen Tunnel (also called the Daspoort Tunnel). It connects the suburbs of Claremont and Pretoria Gardens with Danville and Phillip Nel Park.
The exposed layers here are fairly small compared to layers in other places where the layers are also exposed, (like through the Wonderboompoort cut through, Theo Martins Gateway cut through etc.). Between each deposit of sediment there were also changes including directional and content changes leading to hue of colours one can see from a pale yellow to black in places. Each layer is relative to each other due to successive deposit processes over time. The youngest layers are on top and the oldest layers are on the bottom.
This is called sedimentary strata and is normally horizontal when deposited. If not horizontal, it is due to movement of the earth's crust in some way/direction or another. See this article for some further reading on this subject: http://en.wikipedia.org/wiki/Vredefort_crater
Movement of the crust - upliftment.
This so called upliftment as can be seen from the above article is due to some massive or extreme impact on the earth's surface. i.e. an asteroid collided (or "bounced") against the earth causing a crater and the surrounding earth to shift away, resulting in for example what is today the largest such visible structure on the earth's surface called the Vredefort dome! The asteroid that caused this is estimated at 10km diameter, or approximately the size of Table Mountain in Cape Town!
The Vredefort Crater(Ack: http://lists10.com/top-10-biggest-known-asteroid-hits-earth/)
Please be safe when when logging this Earth cache, as it is located near a busy road.
Questions:
1. Why are the layers not horizontal as to be expected by sedimentary rock?
2. From which direction would that have happened?
3. Standing at GZ, was photo A take east or west of the road through the tunnel (assuming the road runs true North/South)? (Its funny when you as CO do not see the confusion, but let's put it slightly differently: Is photo A the East wall or the West wall? photo B is the opposite side...)
4. Relative to the road surface, what is the angle of dip of these layers?
You may PM the answers to the CO so long, but may log the EC so long. If there are any issues with your answers, you will be contacted by the CO.