To log this earthcache send an email with the following information.
- The Law of Superpositioning GC4YDBR
- Measure the thickness of the dark, layer rich in remains of living things.
- In the middle of the dark layer, there is a layer of light sedimentary rock. Measure the thickness of this layer.
- Take a bearing of the bent rock layer. What heading does this bent rock layer bend towards?
- Form a hypothesis: what could cause the rock in this location to bend, but the rock only 75 feet away to remain flat and unbent? What leads you to form this hypothesis?
- From your observations, does the law of super-positioning stand true? Why do you say so?
Have you ever wondered if a rock could bend? Here’s your chance to find out.
Sediments are rocks and minerals that have weathered and eroded. When rocks weather, they either weather mechanically (change size and shape by breaking apart) or chemically (dissolve, add or remove chemical components). Water, wind, ice and gravity move the weathered sediments. Over time, the sediments accumulate layer upon layer upon layer. Most often, these sediments accumulate in lakes and shallow seas. Current observations show these sediments form flat, parallel layers.
Over time, pressure builds on the lowest layers. Chemicals dissolve in the upper layers and move downward. The combination of pressure and chemicals squeeze rocks together and act as a glue to bind the sediments together.
The law of super-positioning is a basic understanding of sedimentary rocks. It states, if sediments are left undisturbed, the oldest will be on the bottom layer and the newest will be on top. It can take thousands, if not hundreds of thousands of years for these layers to form.
When a cataclysmic event happens on earth, the type of sediments change. Periods of world wide volcanic activity sends ash into the atmosphere and that ash settles to become a new sedimentary layer.
During periods of mass extinction where the majority of life on earth has perished, the remains settle on the bottom of the lakes and seas and get covered by sediments. These remains slowly decompose and become sedimentary rock themselves as coal or the liquid remains gather in underground caverns and become oil and natural gas. Rock rich in remains typically are darker than sediments that are not rich in remains.
Summary:
- Sediments settle in low water areas and make layers.
- These layers form parallel layers.
- If it left undisturbed, the oldest layer will be on the bottom, the newest layer will be on top.
- Layers rich in remains of living things are typically darker than layers that are not rich in remains.
- Periods of cataclysmic events mark drastic changes in rock layers.
The site you are standing next to is a window into earth’s past. Seventy five feet to the east, the layers are nearly as flat and parallel as when they were deposited and formed. The spot you are standing is different. Something happened here. The layers are bent! Something happened to cause this spot to bend and only 75 feet away to remain flat. What can cause rock in a very small, local area to bend like this and the layers around to remain flat and undisturbed?
Examine the bent rock layers and the flat parallel areas to the east. Find the same layers in both areas and examine them for thickness, composition and color. What similarities and/or differences do you discover between the layers. From your examination does the law of super-positioning hold true? Are the oldest layers still on the bottom or has it changed?