• Question: how can you tell what is the oldest rock on this planet or any where else and how do you extract it without damaging it

    Asked by madscientist101 to Aime, Akshat, Diana, Gemma, Judith on 23 Jun 2011.
    • Photo: Judith McCann

      Judith McCann answered on 20 Jun 2011:

      Basically geologists tended to use the fossils that they found within rock layers to determine what ages the rocks where, this was standard practice (despite a lot of overlap and guess-timates) until people realised that radioactive materials have a standard decay time-known as a half life (so if the half life is ten years, half of the radioactive material would have changed into a more stable isotope). Since there are a few kinds of radioactive material (not dangerous as they are in low levels) that are naturally occuring these are used. By measuring the amount of the radioactive isotope left in the material they can figure out the percentage that has changed and so the age of the material.

      The most common of there is carbon-14, or carbon dating, carbon 14 has a half life of 5730 years so it can be used to determine the age of things up to I think 50,000yrs. Different materials can be used to determine the ages of older materials, the main problem being that with the really very long half lifes we do no know how reliable the decay rate is .i.e if we are measuring it accurately.

      I would assume that the oldest rock on earth was formed after the surface of the earth cooled, or is a meteorite. I don’t think I understand the “extract it” part of the question

      P.S an isotope is an atom that has extra neutrons (sub atomic particles that have no charge)

    • Photo: Gemma Sharp

      Gemma Sharp answered on 23 Jun 2011:

      Good answer from Judith there 🙂 not really much I can add!

    • Photo: Akshat Rathi

      Akshat Rathi answered on 23 Jun 2011:

      Judith answered the question about how to tell the ‘oldest’ rock from the others.

      I’ll try to answer your ‘extract it’ question. I am assuming you mean to ask how can you remove it from its place without damaging it, right?

      Geologists and archaeologists work very carefully when trying to remove old fossils (rocks). They use the standard digging equipment to reach the point where they may find a fossil and then by using tools of artists (like those of a sculptor chisel and hammer and those of a painter brushes of different size) they very carefully remove the fossil from its position to study it further.

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