• Question: How do you now its an old rock

    Asked by fendt to Laura on 17 Jun 2013.
    • Photo: Laura Roberts Artal

      Laura Roberts Artal answered on 17 Jun 2013:

      There are two main ways to know how old a rock is:
      1) We can use fossils – rock layers with the same fossils in them must be of the same age (or very similar). Studying the rocks in southern England, geologists in the 18th and 19th Century were able to establish which fossils were younger or older than others.
      2)Once scientist understood about how radioactive minerals decay, they were able to obtain absolute ages of rocks using a technique called radiometric dating. The ratio of parent isotopes (a kind of radioactive material) against the number of daughter isotopes in a rock, tells you how old that rock, or fossil is.

Comments

  • Photo: themightypinhead

    themightypinhead commented on :

    what type of rock is the great canyon made out of?

  • Photo: bvbarmy1234

    bvbarmy1234 commented on :

    Its made up from…. Vishnu schist,tapeats sandstone,bright angel shale,mauv limestone,redwall limestone,supai group,hermit shale,coconio sandstone,toroweap formation & Kaibab limestone ! 😀

  • Photo: Laura

    Laura commented on :

    It is mostly made up of rocks know as Sedimentary rocks. These rocks form tiny tiny little pieces of other rocks that have been eroded away from the surfance of the earth over millions of years. They collect in layers and as they are loaded from the top by more heavy material they are compacted and become sedimantary rocks. They can form in many environments: the sea, rivers, deltas, just on the surface of the planet. The ones in the grand canyon formed ina water environment.