This EarthCache will bring you to a fossilised tree, situated at the east lawn of the Natural History Museum. It is believed to have remained in place since the 1970s. Unearthed in 1854, it has been a part of the Museum's collection since 1873, which ranks it among the most enduring exhibits.
Type of Earthcache: Mineralogy / Paleontology, fossilisation.
About this tree
This fossil tree, identified as Pitys withamii1, was found approximately 56 metres below the surface at Craigleith Quarry, a site well-known for its fossil trees, the first of which was discovered in 1826. It lived during the Carboniferous Period, which lasted from around 359 to 299 million years ago.
Initially believed to be an ancient conifer, the specimen was later identified as a type of seed fern, known as pteridosperm. These plants would have boasted large, fern-like fronds emerging from the top of their tall trunks, reproducing via seeds. Seed ferns, now extinct, possessed a distinctive set of features not found in modern-day plants.
The fossilization process causes a specimen to weigh approximately three times more than regular wood. While the precise weight of the fossilised tree before you is uncertain, it is estimated to be about 11 tonnes.
What is a fossil?
Fossils are the preserved remains of plants and animals whose bodies were buried in sediments, such as sand and mud, under ancient seas, lakes and rivers. Fossils also include any preserved trace of life that is typically more than 10 000 years old. Preserved evidence of the body parts of ancient animals, plants and other life forms are called 'body fossils'. 'Trace fossils' are the evidence left by organisms in sediment, such as footprints, burrows and plant roots.2
How fossils are formed.
There are four main ways of describing fossil preservation: petrification, compression, moulds and casts, and preserved remains.3, for the purpose of the EarthCache, we focus on petrification.
Petrification is a process of fossilisation in which dissolved minerals replace organic matter. When an animal is buried by sediment, such as sand or silt, shortly after it dies, its bones are protected from rotting. As its body decomposes, all the fleshy parts wear away and only the hard parts, like bones, teeth, and horns, are left behind. Over millions of years, water in the nearby rocks surrounds these hard parts, and minerals in the water replace them, bit by bit.4
Silicates, iron oxides, metal sulfides, native elements, carbonates, and sulfates can be involved in permineralization5. Colour is provided by traces of copper, iron and other minerals, while pure silica is colourless. Eventually, minerals completely replace the organic material, and the remains are literally turned into stone or 'petrified'.
More fossil trees in Hintze Hall
The east garden's specimen is not the sole fossil tree exhibited at the Natural History Museum. Within Hintze Hall, visitors can find an additional four fossil tree specimens. Originating from four distinct geological eras, they span from a 385-million-year-old Devonian specimen to one that dates back 25-56 million years. The diverse climates and atmospheres in which these trees flourished have left their mark on these trees, offering insights into the ancient environments they once inhabited.
Natural History Museum - Operating hours.
The gardens are free to enter without a ticket. The east garden will be open daily 10.00-17.50 and the west garden will be open during daylight hours. The Museum itself is open from Monday to Sunday 10:00-17:50 (last entry at 17:30) and is also free to enter. (Unless otherwise stated on the website).
How to claim this EarthCache?
Send me the following by email or Message Center;
1. The text "GCARAG0 Natural History Museum - Petrified Wood" on the first line.
2. The answers to the following questions;
- Observe the tree, are you looking at old wood, or actual rock?
- Are you able to see bark? Describe its appearance (shine/colour).
- Are you able to see tree-rings? If yes, how old was this tree when it died?
- Do you consider this tree specimen a body fossil or a trace fossil?
3. Take a selfie (optional) and/or a photo of a thumbs-up, peace-symbol (V) or personal item, clearly showing the fossilised tree in the background, and attach it to your log.*
References
1 The Fossil Tree, Natural History Museum website, retrieved 06/2024. 2 British Geological Survey, Fossils and geological time (Retrieved 02/2024). 3 British Geological Survey, Fossils and geological time (Retrieved 02/2024).
4 American Museum of Natural History, Dinosaur bones (Retrieved 02/2024).
5 Modes of Fossil Preservation, Schopf J.M. (1975), Review of Palaeobotany and Palynology, vol 20: pp. 27-53.
* Effective immediately from 10 June 2019, photo requirements are permitted on EarthCaches. This task is not optional, it is an addition to existing logging tasks! Logs that do not meet all requirements posed will no longer be accepted.
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