• Question: Which wood petrifies the most easily

    Asked by amazibogles14 to Karen on 12 Nov 2013.
    • Photo: Karen Bacon

      Karen Bacon answered on 12 Nov 2013:

      Hi amazibogles14!
      Thanks for the question. Pretty much any tree wood can be petrified and there is no real difference in terms of petrification between hardwoods (mostly trees that flower like oak) and softwoods (mostly conifer trees like pine). What really matters most is the opportunity to be petrified! Petrification is really interesting because it allows palaeobotanists to see the internal structure of fossil plants – this is great because then we can investigate how ancient plants functioned.

      In order to be petrified, a piece of wood needs to experience a specific set of conditions. Firstly, the wood has to be in conditions where it will not be broken down by bacteria – this usually means conditions where oxygen is limited or absent. We call this anoxic conditions. This is usually means that the wood is submersed in water. That alone is not enough for the wood to become petrified. There needs to be lots of dissolved minerals in the water, usually in the form of silicon oxides (SiO2). Once the piece of wood is nice and waterlogged, both water and dissolved minerals will permeate all of the cells and tissues. The dissolved minerals then precipitate and becomes hard around and within the plant fragment. Once the mineral is completely solidified, the log is effectively encased in solid rock and preserved.

      There are lots of examples of really well-preserved petrified wood. Usually, such preservation happens in a particular area and will preserve many bits of trees. The necessary silica is usually from a volcanic eruption. Some examples of really well-preserved fossil woods are in Arizona (Petrified Forest National Park); Washington state (Ginkgo Petrified Forest) and at many locations in England and Wales, for example at Fossil Forest in Dorset. The fossils also span a really long time, for example the petrified forest in Arizona is from the Triassic (over 200 million years old) and the forest in Washington state is from the Miocene (over 10 million years old). Most petrified wood in the UK is from the Jurassic (between 201 and 145 million years ago)