Rules of relative dating
Relative time places events or formations in order based on their position within the rock record relative to one another using six principles of relative dating.
Relative time can not determine the actual year a material was deposited or how long deposition lasted; it simply tell us which events came first.
The principle of intrusion states that if a body of rock contains intrusions of another type of rock, it must be younger than the source rock Principle of Biostratic Fossil Correlation states that if an index fossil of a known age is found in a rock formation, that formation is of the same approximate age as the index fossil.
This principle represents a modern extrapolation of the older principle of floral and faunal succession, which noted increasing complexity of creatures in successively younger rock strata.
This means that a quartz sandstone deposited 500 million years ago will look very similar to a quartz sandstone deposited 50 years ago.
Making this processes even more difficult is the fact that due to plate tectonics some rock layers have been uplifted into mountains and eroded while others have subsided to form basins and be buried by younger sediments.
It estimates the order of prehistoric and geological events were determined by using basic stratigraphic rules, and by observing where fossil organisms lay in the geological record, stratified bands of rocks present throughout the world.
Though relative dating can determine the order in which a series of events occurred, not when they occurred, it is in no way inferior to radiometric dating; in fact, relative dating by biostratigraphy is the preferred method in paleontology, and is in some respects more accurate.(Stanley, 167-9) Principles The principles of relative dating use a combination of fossil study and structural interpretation to learn about the geological history of an area.
Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this instant, the Earth's surface is moving and changing.As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils.The rules of relative dating for continuous stratigraphic sequences were worked out long ago, by scientists such as Nicolas Steno (1638-86): The Law of superposition states that in any undisturbed geologic sequence, older beds lie below younger beds.The principle of original horizontality states that whether rock beds are deformed or not, they were originally deposited on a horizontal surface.
With this in mind geologist have long known that the deeper a sedimentary rock layer is the older it is, but how old?