Tooting Commons, a beloved green space in South London, hides a prehistoric treasure: a fossilised tree stump from the Jurassic era. This monument is more than a curiosity; it's a portal into Earth's deep past. This EarthCache invites you to explore its origins, geological context, and the story of the species it represents.
Type of Earthcache: Mineralogy / Paleontology, fossilisation.
About this tree
This fossil at Tooting Commons originated from the Purbeck Fossil Forest, a geological formation near Lulworth Cove in Dorset that was once a coastal lagoon during the late Jurassic to early Cretaceous period, approximately 145 to 150 million years ago. The forest was periodically submerged by rising seas, which led to the fossilisation of tree stumps through mineral replacement, primarily calcite and silica, preserving their form in limestone.
The fossil tree is believed to be from the genus Pine (Pinus), though precise identification is difficult due to the nature of fossilisation. Trees in the Purbeck Fossil Forest were typically coniferous, adapted to the warm, coastal conditions of the time. These pines stood in shallow soils, surrounded by ferns and cycads, forming a subtropical forest ecosystem that thrived before the age of flowering plants.
The stump now on Tooting Common was gifted by Victorian developer Alfred Heaver to the Balham & District Antiquarian and Natural History Society. Placed on the common in 1898 by the London County Council, the fossil tree is a legacy of Victorian naturalists seeking to promote public education and appreciation of natural history. It was part of a broader movement to make science accessible to all. The 2018 restoration reflects modern values of heritage conservation, ensuring that geological landmarks remain protected and informative for future generations.
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.1
How fossils are formed.
There are four main ways of describing fossil preservation: petrification, compression, moulds and casts, and preserved remains.2, 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.3
Silicates, iron oxides, metal sulfides, native elements, carbonates, and sulfates can be involved in permineralization4. 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'.
How to claim this EarthCache?
Send me the following by email or Message Center;
1. The text "GCBBFC0 Tooting Common Fossil Tree" on the first line.
2. The answers to the following questions;
- What type of rock surrounded the fossilised tree stump, and what does this tell us about the environment in which it fossilised?
- Based on its age (approximately 145–150 million years), which geological period does the tree belong to?
- What process led to the preservation of this tree as a fossil? Can you identify signs of mineral replacement or sediment layering?
- Why might trees in the Purbeck Fossil Forest have fossilised while others did not?
- Estimate the diameter of the fossil stump. What does this suggest about the size of the original tree?
- Can you spot any growth rings or textures that hint at the tree's age or growth conditions?
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 British Geological Survey, Fossils and geological time (Retrieved 02/2024). 2 British Geological Survey, Fossils and geological time (Retrieved 02/2024).
3 American Museum of Natural History, Dinosaur bones (Retrieved 02/2024).
4 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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