What is Relative Age? - Definition & Effect
As a member, you'll also get unlimited access to over 55, lessons relative dating of rocks definition math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed. Log in or sign up to add this lesson to a Custom Course. Login or Sign up. Geologic time extends back 4. Because the earth is so old and rocks formed millions of years ago, geologists needed a way to date rocks and rock units called strata.
Today there are two common practices for dating rocks and strata. The first is called absolute datingwhere geologists use radioactive decay to determine the actual age of a rock. The second is by using relative dating techniques. 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.
How would you do it? What can you deduce from the rocks? Geologists use what they see and some simple strategies to relative date the rock layers found in the Grand Canyon. Relative dating doesn't really give us an actual 'age,' but it does put things in sequential order. This allows geologists to determine the age of a rock or strata relative to another rock or strata. So, instead of saying when something happened, it puts events in the order they happened. 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.
Principle of original horizontality: This principle simply states that deposition of rocks occurs horizontally or nearly horizontally. Deposition means the process of adding new rock. Most deposition occurs as the ocean deposits sediment flat and horizontally on existing rock, either on the ocean floor or on the continent. Sediments can be deposited on an incline, but this doesn't happen very often. Once the rocks are deposited flat, forces can act upon them to tilt or fold them. This is one of the most basic techniques of relative dating geologists use.
This principle says that the oldest rock layer is always on the bottom and layers above it get progressively younger. To understand this relative dating of rocks definition, consider a four-layer cake. The oldest layer would be the bottom layer. 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.
You can't start with relative dating of rocks definition top layer and add the ones under it since there would be nothing to build on. Principle of later continuity: The principle of lateral continuity says that rocks continue in all lateral directions, even if you can't see them on the surface. This is because the rocks were deposited laterally in continuous flat layers and can be covered with vegetation or eroded in some places.
So, when a valley or relative dating of rocks definition cuts through these rock layers, the principle of lateral continuity says that rocks on either side of the canyon were once joined and continuous. 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. In this case, the principle states that the item doing the cutting is younger than what is being cut.
If we return to our example of the layered cake, the cake has to be there first before you can cut with a knife. In this example above, we have rock layers A - E and Fault F showing. According to superposition, A is the oldest rock layer, while E is the youngest rock layer. However, we also have top rated free dating sites 2015 F present. According to cross-cutting relations, the fault is younger than those layers it cuts. If we put these items in order from oldest to youngest, it would be: A, B, C, Fault F, D, and E.
The reason Fault F is younger than layers A, B, and C is because it cuts the layers. However, it does not cut layers D and E, so those layers are younger than Fault F. This law states that when a relative dating of rocks definition contains pieces or fragments also called inclusions of another rock, these pieces or fragments must be older. To think of it another relative dating of rocks definition, the chocolate chips found in chocolate chip cookies must be made first before they are added to the cookie, right?
You can't make the cookie, then the chocolate chips, and then insert them into the cookie. Principle of fossil succession: This principle is very similar to that of superposition. The only exception is instead of rock layers we're focusing relative dating of rocks definition fossils. These fossils are found in rocks in chronological order in rock strata with the oldest being on the bottom and the youngest at the top.
This can best be explained by looking at fossils embedded in a rock column. Using these techniques allows geologists to determine not only the relative age of rocks but fossils as well. The only way to determine the absolute age of a rock or fossil is by using absolute dating techniques which have relative dating of rocks definition be performed in a lab. These relative dating principles can be applied in the field, so they're really valuable to geologists who spend most of their time researching rocks in nature.
From these principles, we can also learn about the geologic history of the rock or fossil. The relative age of a rock or fossil is not an exact number or age; it's the comparison of one rock or fossil to another to determine which one is older or younger. Relative dating is done by using a variety of techniques that can be easily used when geologists are working in the field and not in a laboratory.
These techniques include the principle of original horizontalitylaw of superpositionprinciple of lateral continuityprinciple of cross-cutting relationslaw of inclusionsand the principle of fossil succession. By using relative dating, geologists learn the order events occurred, as well as relative dating of rocks definition about the hookah hookup pens of the rock or fossil.
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