Dating Rocks Paleomagnetism - Essay Example

Name Tutor Course Date Dating Rocks Introduction Dating and determining how old rocks are is crucial in constructing the history of earth. Geologists depend on two major forms of dating: relative dating and absolute dating. Absolute dating determines the precise number of years that a certain event occurred. It establishes the precise age of rocks and the most significant schemes of absolute dating are based upon the decomposition of naturally present radioactive substances. Relative dating is useful in placing historical occurrences in their exact order of occurrence but it does not give numerical estimations of the number of years the events occurred. Relative dating does not determine absolute age of rocks but it establishes whether a certain rock is younger or older than another. Relative dating of rocks Relative dating of rocks utilizes the superposition principle that builds upon the original horizontality theory. The superposition principle asserts that within underformed series of the sedimentary rocks, every rock layer is elder the layer on top of it and younger than the layer below it. Therefore, the oldest rocks with a series are found underneath with the youngest rocks being at the top. At times, sedimentary rocks are dispensed by incidents like movements of faults that make incisions across layers after the deposition of rocks. This is termed as cross-cutting relationships theory which assumes that every geological feature which incise across strata should have appeared after the rocks that they incise through. Principles of superposition, cross-cutting relationships and original horizontality permit the ordering of events at one area. Nevertheless, they don’t tell the rocks’ relative ages in two diverse locations (Tarbuck, 36). Absolute dating of rocks Radiometric dating technique Majority of absolute age of rocks us attained utilizing radiometric methods. These utilize radioactive minerals within rocks as geological clocks. The atoms of numerous chemical elements possess diverse forms known as isotopes. The isotopes break down with time through a process known as radioactive decay. Every original isotope, usually known as the parent, steadily decomposes to form a novel isotope known as the daughter. Every Isotope is recognized with a mass number. Radioactive elements are usually unsteady atoms that emit particles. The emission of these particles changes the unsteady atoms into diverse, highly stable elements. This is termed as radioactive decay, and it happens at a consistent speed specific to every isotope of every element ((Tarbuck et al, 50). The original radioactive material is known as the parent, while the stable product is known as the daughter. The speed of decomposition is explained by the half life of an isotope, which is the average duration the atom of the radioactive element stays in the parent condition. When half life has passed on, a half of the parent or original element will have decomposed into a daughter element. For instance, Potassium 40 decomposes into Argon 40 having a half life of 1.25 billion years, meaning that at the end of 1.25 billion years, half of the potassium 40 within a rock will have turned into Argon 40.This implies that if the sample of a rock contained equivalent quantities of Argon 40 and Potassium 40, its age will be 1.25 years. If the sample had 3 atoms of Potassium 40 for every single atom of Argon 40, its age will be 625 years and if it had a Potassium 40 atom for each 3 atoms of Argon 40, the age of the rock will be 1.87 billion years (McDougall & Harrison, 72). Majority of radioactive isotopes have the capability of decomposing very fast to be helpful in the determination of the age of rocks. Carbon 14 dating can be used as a method of measuring isotopes that decompose too rapidly, but carbon-14’s half life is around 5730 years, minus or plus forty years. This makes the half life very short for use in dating substances that are millions of years old. Nevertheless, some isotopes decompose very slowly and may be useful in measuring the age of rocks. Such isotope include Uranium 238 which decomposes to a daughter Lead 206 with a half life of four and a half years, Thorium 232 which decomposes to Lead 208 with a half life of fourteen billion years and Rubidium 87 which decomposes into Strontium 87 with a half life 0f 48.8 billion years (Faure, Gunter & Mensing, 79). Depending upon the type of rock under study, radiometric data may offer diverse forms of information. Igneous rocks are formed as a result of cooling of lava or magma, and it has small quantities of radioactive elements. Through establishing the proportion of the parent or original substance to the resultant daughter material following decomposition of the parent material within the igneous rock, a geologist can be able to determine the age of a rock. Following the corrosion of igneous rocks, the eroded substances are settled down to form a different kind of rock known as sedimentary rock (Tarbuck et al 71). Dating the sedimentary rock through the use of radiometric methods will tell how old the parent igneous rock is, and not the period since the formation of the sedimentary rock. However, the age of the parent and daughter rock is similar at times, especially when the explosion of a volcanic leads to deposition of ash on the surface, with the ash being swiftly integrated onto the sediments. Both the age of the sedimentary and the ash will be similar. On the other hand, metamorphic rock forms as a result of prior rock intense pressure and heat. Metamorphism might reorganize a number of radiometric clocks, so that the radiometric dates trace the period of alteration other than the period when the prior rock coagulated from magma or when it was put down as residue (Ludwig & Renne, 105). Paleomagnetism technique The earth is similar to a very big magnet. It possesses a magnetic south and north pole with its magnetic field being everywhere. Similar to the way a compass’ magnetic needle points towards magnetic north, minute minerals that naturally occur in rocks usually point toward magnetic north, almost parallel to the magnetic field of the earth. As a result, magnetic minerals found in rocks can record the polarity or orientation of magnetic field of the earth. Through geological period, polarity of magnetic field of the earth has changed, leading to reversals in polarity. If magnetic north pole is near geographic North Pole the polarity is normal while reversed polarity if magnetic north is close to geographic South Pole (Ludwig, & Renne, 72). Utilizing radiometric measurements and dates of prehistoric magnetic polarity within sedimentary and volcanic rocks, usually known as paleomagnetism, geologists can precisely establish when magnetic reversals took place in ancient times. Ludwig and Renne, (86) note that combined examinations of this kind have resulted to the generation of geomagnetic polarity time scale abbreviated as GPTS. GPTS is split into durations of reversed polarity and normal polarity. Geologists may gauge rocks’ paleomagnetism at a place to tell its recording of historic magnetic reversals. Each reversal appears same in the record of rock, so additional lines of proof are required to compare the place to GPTS. Data like radiometric dates may be utilized in correlating a certain paleomagnetic reversal to a well known reversal within GPTS. After relating a single reversal to GPTS, then it is possible to establish the actual age of the whole sequence (Ludwig, & Renne, 90). Conclusion Geologists can establish the age of rocks using a wide range of techniques. Relative dating techniques are utilized to tell a series of incidents and it is achieved using the principles of superposition, cross-cutting relationships and original horizontality to reveal incidents that took place in rocks from the oldest to the youngest. In absolute dating, geologists establish the exact time that has passed since the formation of rocks through gauging the radioactive decomposition of isotopes. Paleomagnetism gauges the prehistoric orientation of magnetic field of the earth to help geologists in establishing rocks’ ages. Works Cited Tarbuck, Edward. Lutgens, Fredrick., & Tasa, Dennis. Earth: An introduction to physical geology. Prentice Hall: New York, 2013. Ludwig, Kenneth,. & Renne, Lisa. Essentials of paleomagnetism. Berkeley, CA: University of California Press, 2012. Faure, Gunter. & Mensing, Teresa. Isotopes: Principles and Applications. New York: John Wiley and Sons, 2012. Ludwig, Kenneth & Renne, Paul. Geochronology on the paleoanthropological time scale, Evolutionary Anthropology 9, 101-110, 2010. McDougall, Ian & Harrison, Mark. Geochronology and thermochronology by the 40Ar/39Ar method. Oxford, UK: Oxford University Press, 2010. Read More