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When stress caused by friction produced by the Earths movements and the natural rigidity of the rock builds up in rocks and reached a level that is over the strain threshold, the energy released resulted into a fault. The compressional fault, also known as reverse fault has the hanging wall moving up relative to the foot wall. The movement will expose the older rocks on the hanging wall at the surface. On the other hand, when the hanging wall moves down relative to the foot wall it is called a tensional fault or normal fault. Sometimes, faults are reactivated at a later time with the movement in the opposite direction to the original movement (this is called a fault inversion) and thus a normal fault may therefore become a reverse fault and vice versa. The reverse fault is indicative of the shortening of the Earths crust and its dip of fault is relatively steep, greater than 45.
Although the trust fault has basically the same movement as the reverse fault, the dip of its fault plane is usually less than 45. Thrust faults are what usually form ramps, flats and fault-bend (hanging wall and foot wall) folds. The difference between the different categories of slips basically lies on the sense of movement on the fault plane. A fault where the slip on the fault plane is vertical is known as a dip-slip fault. While, if the main sense of slip is horizontal the fault is known as a trans-current or strike-slip fault. Anticlines and Sync lines are rock layer forms that are pushed together.
Anticlines are folds in which the oldest rock lies in the center or core and sync lines have the youngest rock in its center or core. Most often anticlines are arch shaped and sync lines are trough shaped. The geological time scale is a measuring method used by geologists and other scientists to describe and calculate the timing and relationships between events that have occurred during the history of Earth as well as the emergence and extinction of life forms in the planet. It was originally laid out using relative age-dating principles. The largest defined unit of time is the super-eon comprised of four major eons: Phanerozoic the oldest where the simplest life forms first started; followed by Proterozoic, the eon for big Jurassic animals; the Archean where pre-modern plants and fauna made their appearance and finally the Hadean to which our modern Earth belong. Eons are divided into Eras, which are in turn divided into Periods, Epochs and Stages.
A numerical (or "absolute") geologic age-dating is a method of measuring the specific number of years, like 150 million years ago, of fossils excavated in the layers of the Earth. A relative geologic age-dating, on one hand, is simply a comparative judgment that states whether one rock formation is older or younger than another formation. Relative geologic age dating uses observations of factors related to a rock which allow assumptions about the age of the rock compared to other rocks or its surroundings by the examination of the order of sediment layers as well as their relative positions. This is a good method for dating sedimentary rocks. The absolute age-dating uses knowledge about the decomposition of radioactive isotopes in the rock; then considering the half life of the isotope which allows for the calculation of the rock age. This is very useful in dating igneous (volcanic) rocks.
Works Cited Science Course Ware. Radioactive Isotopes - the "Clocks in Rocks. " N. D. 29 November 2007. p. 1. Truck, Edward J. and Frederick K.
Lutgens. Earth Science. Upper Saddle River: Prentice Hall, 2000.
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Research essay sample on Relative Geologic Age Dating Geologic Age Dating Fault
