How were fossils made

How are fossils formed?

Remains of formerly living organisms that have survived through preservation (hermetically sealed) are known under the term fossils. But how did ancient animals and plants become fossilized? Fossils are mainly found in stratified rocks (sediments). In general, the remains of an organism are called fossils if they have been (chemically) changed by the surrounding rock and the substances it contains.

As a rule, an organism begins to decay after it dies. The soft components of his body disintegrate and are removed by scavengers or broken down by microorganisms such as bacteria or fungi. If the remains of an organism are covered with sediment and sealed off from the outside world, the material changes under the influence of the pressure and temperature of the rock layers above it.


On the one hand, the shell or bone material is deformed by the pressure; on the other hand, it is chemically changed by the inflow of saline solutions from the surrounding rock. One speaks of fossilization when a stone covering forms around a body.

When the organic components of the shell or bones are completely dissolved and the resulting cavity in the rock is filled with inorganic matter, an imprint is created from the exterior of the fossil. It can also happen that only the soft parts of an organism are dissolved and replaced by minerals. A so-called stone core is formed - an imprint from the inside of the animal.



Compared to the mainland, water with its changing currents favors the formation of fossils. A dead mussel is quickly covered by sand or silt, which makes fossilization more likely. Therefore, there are also a considerably larger number in the water. In the country, you will find what you are looking for in tar pits, swamps or in the polar regions, where whole mammoths have been preserved as fossil mummies.

Weathering and deformation of the earth's crust can destroy the witnesses of the past again. That is why, with increasing age of the rock layer, fewer and fewer fossils are found until they disappear completely in the oldest layers.


Source: Image 1,3 copyright M. Fischer, Medienwerkstatt

Image 2 copyright