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What's a fossil?
Fossils are the remains of ancient seashells embedded in rocks, but also bones and teeth of animals from the past, insects trapped in amber, petrified trunks of large trees, footprints left by dinosaurs who walked on a quagmire ... among others. We can say, then, that fossils are remains or traces of plants and animals that lived in a prehistoric past.
How fossils form?
Most fossils were formed when an organism remained burried under sediments, usually under water, just after its death. Under these conditions, fleshy parts decompose and disappear rapidly; whereas hard parts, like bones, does not degrade. Sometimes, these hard structures stay almost intact, but most of the time their pores and open spaces impregnate with minerals brought by water, and all the structure becomes rocky. For petrified wood, the original material can be replaced by minerals, silicon in particular, and some characteristics like the annual growing rings are kept as well as some cellular structures.
In another type of fossilization, the original structure is completely dissolved and only an empty space, or mould, remains in the rock. This mold has the exact shape as the original material. Sometimes, other materials goes inside this mold and produce a copy of the original.
The steps
Step 1 : all starts when an animal dies near water. Flesh decomposes to leave only the bone. When the carcass of an animal is broken, scavengers eat the soft tissue. The hard parts like bones usually manage to suffer little damage for a while. On the contrary, the skeleton may end up disintegrate if left exposed to air. If it is found buried under mud or sand layers under water, it manages to keep his shape.
Step 2 : once the animal dies and decomposes, his bones are covered with water.For thousands of years, sediments like mud and silt accumulate on them and prevent them from being carried away by the current. These sediments also protect bones from erosion and putrefaction.
Stage 3 : gradually, sediments turn into rock. The animal's remains are trapped in the layers of rock. As sediment accumulates, the buried bones undergo changes in the rock. When the dissolved minerals in the water seep and solidify in the bone, the interstices may be "permineralizated". These hard minerals are replacing bone tissue; the structure is completely petrified then, is the petrification.
Step 4 : Finally, the rocks are raised so high that they are now exposed above the water level. These fossilized rocks are then exposed to the forces of nature and climatic variations, which gradually wears them out. Erosion reveals the ancient sediments and bones they contain. It is the appearance of the fossil.
The Earthcache
In this room you will find a wide range of fossils from the Carboniferous (298 Ma), the era of coal formed during the separation of Pangea. This period is characterized by the first big trees, marine life is rich in crinoids, other species of echinoderms and brachiopods are abundant. These fossils come from the pit of Lewarde and can be found also in other mining areas such as the south of Belgium (Mons - Charleroi - Namur) where in southern Poland (Silesia).
Reminder on "Earthcaches": There is no container or logbook on the given coordinates. Just visit the site and answer the questions by e-mail. There is no need to wait for my reply, feel free to log immediately after. If the answers are incorrect, I will let you know. Happy caching!
To validate your visit:
1-. What is the age of a fossil formed during Carboniferous?
2-. Why can't we find dinosaur fossils at the Carboniferous era?
3-. Why can't we find these carboniferous fossil in Paris or London for example?
4-. Find the Neuralethopteris fossil, what was it and what was its size?
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