The principle of uniformitarianism was first stated by James Hutton in the 18th century. To determine the sequence of geologic events, several principles must be followed. The sequence orders the events but provides no information to the amount of time passed or between events. It is a qualitative way of describing the sequence of events. Placing of events in the order in which they occurred without any relationship to the actual time during which any one event occurred is known as relative dating. In determining the absolute age of a rock different methods are used Uranium – Lead, Uranium – Thorium, Potassium – Argon, Rubidium – Strontium, Carbon “Fission Tracks” and Thermoluminescence.Cindy Kearns and Elizabeth Johnson Relative Dating This is used for evaluation of the age of a rock using the so called radiometric methods The final stabile product (isotope) can be compared in quantity to the original radioactive element. Radioactive elements emit α and β particles, as well as γ rays, thus causing their mass to reduce over time, shifting eventually to stabile isotopes. The determination of absolute (radiometric) age of a rock is based on the radioactive decay of isotopes. the discovery of radioactivity that gave to the geologists a “clock” which helped them to define it. For the determination of the “exact” time when certain rocks appeared, it was the beginning of the 20 th century, i.e. the events in Earth’s history (what came first), but not the exact time when those events took place. In defining the order of deposits by relative dating, only the order of deposits has been determined, i.e. This method has been developed as part of paleontology – science concerned with fossils and development of life through geological history. The paleontological method is based on the study and interpretation of animal and vegetal organisms’ evolution during geological history, and in order to determine the relative age of a rock, the principle of superposition is used as a starting point, as well as fossil deposits preserved within a rock. What does this data say about the time of its origin? In order to answer this question, fossils are of crucial importance. The lithology, such as colour, cut, chemical composition, degree of diagenesis, can be used for comparing and determining relative age of a rock, but with the assumption that equal or similar rocks are also contemporary.īy determining the age of a rock, only its chronology is defined. The principle of inclusion states that each rock containing inclusions of a neighbouring rock must be younger than that rock.The principle of superposition is based on the assumption that, in a regular sequence of layers, the oldest layer will be on the bottom of the sequence, while all the other layers are successively more recent.parallel to the surface to which they deposit. The principle of original horizontality departs from the assumption that most of the sedimentary rocks are deposited under the action of gravity, in approximately horizontal layers, i.e. The determination of the relative age of a rock is based on the principle of original horizontality of the sediments, principle of superposition, principle of original lateral continuity, principle of cross-cutting relationships, principle of inclusions, principle of biological succession and the lithology of a rock. Relative age of magmatic and metamorphic rocks is determined according to their relation with sedimentary rocks. In determining the relative age of a rock, the data from sedimentary rocks are generally used. The age, or the chronology of geological creations and events is determined using relative and absolute age. The age of a rock is determined by stratigraphy, a branch in geology which studies the chronology of events and changes, along with the development of organisms, which have determined the development of the Earth from when it became an independent spatial body until today.
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