On this folio, we volition discuss the Principles of Geology. These are general rules, or laws, that nosotros utilize to determine how rocks were created and how they inverse through time. We besides utilize these laws to determine which rock formations are older or younger.

Different rock layers of different colors and angles, labeled A through L.

The Law of Superposition states that beds of rock on superlative are usually younger than those deposited below. This is logical, consider a layered cake or a stack of books, you tin't add together another layer unless 1 already exists to begin with. By agreement the Law of Superposition nosotros can make general statements near the ages of these rock units.Consider these top layers – Unit K (dark green) is younger than Unit J (burnt orangish) considering it lies atop it, this also direct relates to the relative age dating.

The Police of Original Horizontality suggests that all rock layers are originally laid downward (deposited) horizontally and can later be plain-featured. This allows us to infer that something must have happened to the rocks to make them tilted. This includes mount building events, earthquakes, and faulting.The rock layers on the bottom have been plain-featured and are now tilted. The rock layers on the meridian were deposited later the tilting outcome and are over again laid down flat.

The Law of Lateral Continuity suggests that all rock layers are laterally continuous and may be broken up or displaced by later events. This tin happen when a river or stream erodes a portion of the stone layers. This can also happen when faulting occurs. Faulting causes displacement in rock units. The figure here shows the kickoff between the layers signified past the black line cutting across the rocks. Trace the colors or messages beyond to detect the layers that match. The rock layers on the top seem to form a valley but we can tell that Unit I (nighttime blue) on one side is the same every bit the Unit of measurement I (nighttime blue) on the other side. There is missing stone in between and a displacement caused by deformation.

Cross-cutting relationships as well helps us to empathize the timing of events. Younger features cutting beyond older features. Going back to the fault on this paradigm, we know that these stone layers were involved in the error movement because they are all get-go. We can also determine which beds of rock were tilted and that relationship to the rocks that are non tilted. The rock layers on the bottom have been deformed and are now tilted. The stone layers on the top were deposited after the tilting event and are again laid downwards flat.

Conglomerate rock containing many smaller pieces.
Conglomerate rock containing many smaller pieces.

The thought of Components is simple. If you find a rock that has other smaller pieces of rocks inside it, the smaller rocks inside must have existed before the larger rock was created.

The Principle of Faunal Succession states that a species appears, exists for a time, and so goes extinct. Time periods are often recognized by the type of fossils you come across in them. Each fossil has a 'first advent datum' and a 'final appearance datum'. This is simply the oldest recorded occurrence of a fossil and then the youngest recorded occurrence of a fossil.

Rocks that comprise fossils occur in a very real and understandable order. Rocks of certain time periods can be recognized and separated by their fossil content (Boggs, 2012). This is a skill that geologists acquire as they do field piece of work and explore the Globe! The fauna from the Mississippian is very different from the Ordovician and easily distinguishable! Groups of fossils, or fossil assemblages, can exist used to correlate rock units across continents.

Ten vertical rock layers with different fossils. A legend is to the side organizing the fossils from oldest to youngest.
Relative age dating with fossils is very common and nosotros can employ this information to brand interpretations about the environment.

Something else that fits into Geologic Principles and basic stratigraphy (report of rock layers) are unconformities. Unconformities are simply gaps (missing data) in the rock record, these gaps could indicate a variety of processes. Such as: erosion, deformation, or changes in sea-level. There are 3 main types of unconformities: (1) Athwart unconformities; (2) Disconformities and; (3) Nonconformities.

Athwart unconformity between the older orange package of rock layers and the younger dark-green package of rock. The curvy line indicates the erosional surface. A disconformity between the older purple sedimentary layers and the younger orange sedimentary layers. Nonconformities occur between an igneous trunk and sedimentary rock layers.

Athwart unconformities are represented past an older group of rock layers has been tilted, eroded, and some other younger set of rock layers were deposited on top of this erosional surface. The tilting process is commonly past a mount building issue, it doesn't necessarily have to be in the mountains but the effects of mountain building processes are long reaching.

Disconformities are an erosional surface between two sets of rock layers. Unlike with angular unconformities, there is no tilting of the older stone layers. This makes disconformities difficult to recognize because the erosional surface is ofttimes very hard to find.

Nonconformities are unconformities that separate dissimilar rock types. This is commonly the separation between igneous and sedimentary or metamorphic and sedimentary rocks. These types of unconformities ordinarily indicate that a long corporeality of fourth dimension has been eroded away earlier the younger sedimentary rocks were deposited.