Relative dating of rock strata Kinky slave dateing
Long before geologists tried to quantify the age of the Earth they developed techniques to determine which geologic events preceded another, what are termed "relative age” relationships.
These techniques were first articulated by Nicolas Steno, a Dane living in the Medici court of Italy in the 17th C.
Today there are two common practices for dating rocks and strata. Geologists use what they see and some simple strategies to relative date the rock layers found in the Grand Canyon.
The first is called absolute dating, where geologists use radioactive decay to determine the actual age of a rock. Let's say you are a geologist who is tasked with dating the rocks found in the Grand Canyon, and you must do so in the canyon without the aid of any laboratory equipment. Relative dating doesn't really give us an actual 'age,' but it does put things in sequential order.
So, basically it's the difference between saying 'I'm 25 years old, and my sibling is 20 years old' and 'I'm older than my sibling.' Geologists use a variety of techniques, or principles, to determine the relative age of a rock unit.
Principle of original horizontality: This principle simply states that deposition of rocks occurs horizontally or nearly horizontally. Most deposition occurs as the ocean deposits sediment flat and horizontally on existing rock, either on the ocean floor or on the continent.
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If we return to our example of the layered cake, the cake has to be there first before you can cut with a knife.
Principle of cross-cutting relations: The principle is another example of which came first.
Instead of using layers, it involves features that cut through the rock, like a fault or a dike.
To understand this better, consider a four-layer cake. It wouldn't be possible for the other layers to be added without the bottom layer first.
This same process applies with each layer to the cake added.