How old are crustal rocks

How old are crustal rocks

By: Andrea Correa and Lorena Rivera 12-1

14/March/2016

The  Plate tectonics theory consists that the outer rigid layer of the earth  is divided into twenty four  "plates" that move around the earth's surface relative to each other, like slabs of ice on a lake. Basicly the earth consists of the plates, and plate boundaries, those zones where the plates contact and interact. Plates are combinations of two units, continents and ocean basins. L. S. (2000, September 13)
        There are two major earth crusts or plates that include the Eurasian plate, Australian, Indian, Philippine plate, Pacific plate, Juan de Fuca plate, Nazca plate, Cocos plate, North American plate, Caribbean plate, South American plate, African plate, Arabian plate, the Antarctic plate, and the Scotia plate, and consist of smaller sub-plates.
         The oceanic plate, defined as the thinner but denser part of the earth crust more than the continental crust. They are denser than continental tectonic plates. The Oceanic plates are mainly found under the oceans because it is said they are subducts, this means they go under the continental plate. This crust is continuously suffering transformations, destroying and forming again, and it has more activity in difference with continental plates (Enchanted Learning, 1999- 2016).
        The second earth crust is the continental plate or continental crust , are one portion of one block of tectonic plates, they are lighter than oceanic plates, and they are mainly found at destructive plate margins and above oceanic plates because they are not submerged in water (Pacey, 2016).
        Fossils were viewed to determine relative ages, then they discovered  the use of  radioactive isotopes. Radioactive dating is a method of dating rocks and minerals using radioactive isotopes. This method is useful for igneous and metamorphic rocks, which cannot be dated by the stratigraphic correlation method used for sedimentary rocks. I. G. (2009, October 6). Scientists can determine the age of the seafloor thanks to the changing magnetic field of our planet. The currents in the liquid core create the Earth’s magnetic field, reverse themselves: it is called a geomagnetic reversal.To confirm the ages obtained with magnetic records, and get an absolute age of the seafloor, scientists use the radioactive dating technique. When the lava solidifies at the ridges to form the new seafloor, radioactive elements coming from the mantle are trapped in it. By measuring the amount of remaining radioactive elements and daughter products in the seafloor, scientists can determine when the magma crystallized, and know the absolute age of the seafloor. E. (n.d.).
        The patterns scientists observe in the ages and magnetism of ocean rocks was the ones  in the rocks of the ocean floor. This rocks where more helpful than we can think of because scientist found out that they have marks like “stripes”(Phschool, 2013). This stripes were mapped for the volcanic rocks making up the ocean floor that were produced by repeated reversals of the Earth's magnetic field. They have an hypothesis saying that the ocean floor moved away several centimeters per year, they also found there was a remarkable relationship between the ages of the Earth and the striping pattern. With time and gaining experience, scientists were able to date and finds similarities with the magnetic striping of nearly all the ocean floor, which indicates 180 million years old (Banks, 2005).

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