Superposition and Rock Layers
By Hayes
I like this topic because it has always interested me. I have always enjoyed studying rocks. I also have always have had an interest for fossils. I find it neat how scientists can identify age of rock by its position in the earth. I have been interested in the law of superposition since I learned about it. It makes me want to learn about the history of fossils and the earth. This was a very important topic. Also a very comprehendible one. This topic has so many cracks and crevices that you can look into and study. You can look into layers, superposition, types of rock, fossils, and all kinds of other things. This topic is very important to geologists to find the age of rocks even the earth. I have always had a rock collection. I started it when I was probably 4 and I was into it. Just the formation of crystals interested me and I think its very neat how all this rock formed on earth.
Law of Superposition
The Law of Superposition basically states that the layers below are older the farther you go down. In essence the layer below one is older and the layer above is younger. The Law of Superposition is a geochronoligical time scale. It shows geologic time record and also fossil age and rock age based on their position in the rock layer.
Unconformities and Faults
Rock layers can also show major events like a major volcanic eruption. It will show up in the rock layers as an ash layer. They can also show faults and unconformities. A fault is a crack in the rock layer and the other layer sometimes falls to expose other layers to horizontally incorrect layers. An unconformity is where a layer has eroded or been exposed to another layer vertically. They show fossils in the specific layers. They can date the fossils to their relative age by finding the age of the rock on the geologic time scale. This is called relative dating
Intrusions and Volcanic Activity
The rock layers can also have intrusions which are magma layers that can just be a horizontal layer and not disturb other layers or it can seep through old to new layers. This causes a disruption and melting of rock layers and it creates a newer unconformity in the layers. It is an injection of a magma into a preexisting rock layer.
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Rock Layers
Rock layers or stratum are horizontal layers of rock, sediment, igneous material, or a layer of a substance created by earth. They lay horizontally and age youngest to oldest from top to bottom. This is known as the law of superposition. A layer above is younger than the layer below. Scientists can date the earth like this using the time rock layers took to form. They can dig down and use the geologic time scale to help figure out ages of other things. The rock layers are used to make up the geologic time scale and give a layer a time zone.
related links
USGS Rocks and Layers describing rock layers and the law of superposition
Rock Layers Timeline The timeline of the earth and how it works
Ages of Rock Layers Interactive rock age diagram