A important tenet of stratigraphy is the Law of superposition, which asserts that within a series of sedimentary rock layers, the oldest layer is at the bottom and the layers are increasingly younger with ascending order in the sequence. This rule helps geologists to determine the age of rock formations and allows them to place old rocks on top of young ones without being mistaken for having the same age.
Superposition can be used by lawyers as a defense against claims of negligence. For example, if a person is walking along a road and is hit by a car, the driver of the car may claim that the victim was responsible for being in the path of the oncoming vehicle because he or she failed to keep an eye out for traffic. In this case, the law provides that drivers have the right-of-way over pedestrians, so even if it were true that the victim had been too focused on something else (such as his or her cell phone) to see the car approaching, this would not be considered a reason for liability on the part of the driver.
Liability also cannot be imposed just because someone is in the way of an oncoming vehicle. Under California law, for example, people who walk in the paths made by vehicles have only themselves to blame if they are hit because it is obvious where the road will take you if you fail to look up from your cell phone for even one second.
The Law of Superposition is a key principle of archaeology. Given typical deposition circumstances, the law dictates that younger strata will be deposited on top of older strata. This concept serves as the driving principle for stratigraphy, which is the study of geological or soil strata.
Stratigraphy is useful for dating ancient structures and artifacts because layers of different materials (such as clay, sand, and gravel) become fossilized over time due to changes in temperature and humidity. The further back in time we go, the more distant locations archaeological remains are found. Thus, scientists can use stratigraphic analysis to date ancient objects and sites.
Stratigraphy is also important for identifying physical changes in the Earth's surface through time. For example, if you were to look at the cliffs near San Diego, California, you would see that they are made up of large rocks that are often weathered into a smooth shape. However, under certain conditions, these same rocks might be covered with sediment that was once water. Using stratigraphy, we can tell that many millions of years ago, before any plants or animals lived here, the area must have been underwater.
Finally, stratigraphy helps us to understand how the Earth's surface has changed over time by examining the remains of past life forms.
According to the Law of Superposition, the material on which every layer is formed is older than the layer itself in a layered, depositional sequence (such as a series of sedimentary beds or lava flows). As a result, the layers become younger as one progresses from bottom to top. For example, if a geologist finds fossils in a rock formation that are estimated to be 10 million years old, then that means the original rock forming the habitat for the fossils was once under water. Over time, more and more of this original rock will have been submerged by sea level changes or eroded away due to weathering. The remaining portion can now be exposed by future rises in sea level or else new rock may be deposited on it.
Fossils are remnants or remains of ancient organisms. Fossils are commonly found in sedimentary rocks because sediment is easily eroded away from hard objects such as bones or shells of dead organisms. As erosion removes the top layer of rock, new materials are brought into view to replace the ones that were lost. So, over time, all of the elements that went into making up the original organism are recycled into new forms that can be preserved for later study.
Sedimentary rocks are shaped by gravity and wind. Sediment is any finely divided material that is slowly moved by fluid currents or winds. Some common examples of sedimentary rocks include sandstones, shales, and conglomerates.
Sedimentary rocks form in flat strata. To begin, they employ the rule of superposition to establish the relative ages of sedimentary rock strata. According to the rule of superposition, the oldest sedimentary rock layer lies at the bottom of a horizontal sedimentary rock layer. Each layer above it is younger than the layer beneath it. For example, if we were to examine a section of shale that was deposited during a waterlogged environment, such as a lake bed, we would see that it is generally dark colored with some light and dark-colored shales interspersed throughout. The presence of white or light-colored sand between darker shale fragments indicates that there was more open water than sand when the layer was deposited. This is because water blocks out sunlight which results in darker sediments forming near where it rained most often (in freshwater environments) or in shallow waters (in marine environments).
The rule of superposition can be used to determine the relative age of these layers. For example, if we were to examine a section of shale that was deposited over many years, we could say with confidence that the oldest layer is likely black with some lighter-colored material mixed in. Any material below this first layer and above the underlying blue clay deposit would be younger than the black shale.
This method can also be used with success to determine the relative age of other types of rock including limestone, dolomite, and gypsum.
To establish the relative age of a layer of sedimentary rock, scientists employ a fundamental principle known as the Law of Superposition. As a result, scientists might presume that non-horizontal sedimentary rock strata were tilted or distorted by crustal processes that occurred after the layers originated. For example, if a rock layer is not horizontal, then it must have been under some form of stress when it was laid down.
Geologists use this fact to try and determine the order in which different rock formations were deposited during periods of time when stress levels were low. They can also apply it to predict how the Earth's surface would look had certain major events in its history not taken place. For example, if a mountain range was formed when two continents collided, then geologists can infer that pre-existing faults within the continents' surfaces would have been overlain by their joined-up edges.
The Law of Superposition was first proposed by French mathematician Pierre Louis Maupertuis in 1698. He called it "the foundation of modern geometry" because he believed it could be used to prove many geometric propositions that had previously only been proved by indirect methods.
In conclusion, the Law of Superposition is one of the most important tools in GEology because it helps scientists to understand how the Earth's surface was shaped over time through geological processes.
According to the rule of superposition, each rock layer is older than the one above it. As a result, the relative age of the rock or fossil in the rock is older if it is deeper in the rock strata. For example, if you were to dig down through several rock layers, you would eventually reach ancient marine fossils such as coral and shells. These fossils are very old -- they date back before many of the modern plants and animals existed -- so they provide evidence of early life on Earth. You would also likely find modern plant and animal remains near the top of the hole because they are newer than the fossils.
In conclusion, the law of superposition tells us that each layer of rock is always younger than the one above it. If you were to dig down through several rock layers, you would eventually reach ancient marine fossils such as coral and shells.