"Geologists have a saying - Rocks remember" - Neil Armstrong
Petrified wood
A fossil is a physical memory of life that existed on earth millions of years ago. Petrified wood is a type of fossil, a fossil of a tree or plant. Petrifaction is the result of a tree having been replaced by stone via a mineralization process. The organic materials making up cell walls have been replicated with minerals (mostly silica in the form of opal, chalcedony, or quartz). In some instances, the original structure of the stem tissue may be partially retained. Unlike other plant fossils, which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material.
The petrifaction process occurs underground, when wood becomes buried in water-saturated sediment or volcanic ash. The presence of water reduces the availability of oxygen which inhibits aerobic decomposition by bacteria and fungi. Mineral-laden water flowing through the sediments may lead to permineralization, which occurs when minerals precipitate out of solution filling the interiors of cells and other empty spaces. During replacement, the plant's cell walls (lignin) act as a template for mineralization. Most of the organic matter often decomposes, however some of the lignin may remain. Petrified wood is most commonly associated with trees that were buried in fine grained sediments of deltas and floodplains or volcanic lahars and ash beds. Petrified wood is found worldwide in sedimentary beds ranging in age from the Devonian (about 390 million years ago), when woody plants first appeared on dry land, to nearly the present.
More specifically...
The National Arboretum in Canberra is home to thousands of trees, including the National Bonsai and Penjing Collection, now housed on-site. In amongst the bonsai are located a number of petrified wood fossils, including a165 million year old petrified tree stump donated by the National Dinosaur Museum. A rare fossil dating back to the Jurassic era, this tree stump comes from the Wandoan region in Queensland, where numerous other fossils have been found, including petrified wood and tree ferns.
In the Jurrasic era, the Wandoan region included many swamps and rivers and was located close to the south pole. The Wandoan sediments were ideal for the preservation of plant material as they were rich in silica. The Wandoan area is also home to significant coal deposits.
To log this earthcache,
Task 1: Please submit your answers to the following questions to me via theGeocaching.com messaging facility. You may use information from this description, at GZ, or do some additional research to support your answers.
- Question A: What do you think is the main mineral that makes up the petrified tree stump? How did you come to this conclusion?
- Question B: Describe the texture of the petrified tree stump, including its shape, and the size/colour of the minerals?
- Question C: What environmental conditions do you think would be needed for petrified wood to form?
- Question D: How many other petrified wood fossils can you see on display in the same space?
Task 2: Please post a picture of yourself (or part of your self, or your name) with the petrified tree stump in the background as part of your log to provide evidence you visited the location. Please do not post close-up images of the tree stump.
You may log your find immediately and send your answers to me within a week of logging. Logs with no answers provided or no photographic evidence you were at GZ may be deleted. Please do not include answers to the questions in your log. Also, please enjoy and be respectful of the bonsai on display as you move around the space!
The National Bonsai and Penjing Collection at the National Arboretum is open daily from 9am to 4pm, except for Christmas Day.
Congratulations to StarsAlign, Mountainsbeyond, Flintones and Tankengine for a joint FTF!