How Do Fossils Form?

The branch of Earth sciences which studies fossils and related remains is known as 'paleontology'. It is one of the most important attributes of archeology, considering that our knowledge about the prehistoric times depends on these fossils to a significant extent.

In course of fossil hunting, archaeologists have come across fossils which belong to the period stretching back to 3.5 billion years ago. However, most of our knowledge about the Earth is derived from remains belonging to the last 600 million years. If it were not for the formation of these fossils, several questions about human evolution and existence would have still been a mystery to us.

Going by the simplest definition possible, fossils are remains or imprints of plants and animals that are found captured in the surface of the Earth. When we hear the term 'fossil', the first thing to cross our mind is a dinosaur, which isn't surprising, considering that most of the information that we have about these gigantic creatures is based on fossil evidence alone. When we talk about fossil remains, we most often stress on bones, shells, teeth, leaves, etc.

In a broad sense, however, this term also refers to the remains of various activities attributed to animals and plants. While bones and teeth are referred to as 'body fossils', footprints and caves are referred to as 'trace fossils' and organic compounds are referred to as 'chemical fossils'.

The foremost thing you need to understand when it comes to the formation of fossils is that every plant and animal is not subjected to fossilization. While a vast majority of these plant and animal remains decay and disappear, a few are subjected to conditions ideal for this process.

Though fossilization can occur anywhere, the chances of this are maximum in water bodies, such as river beds and ocean floor. Even plants and animals that die on land are eventually swept in these water bodies, where they eventually get fossilized.

In order to get fossilized, the plant or animal has to get trapped in some material. In most of the cases, sedimentary rocks act as this material. In the process of formation of sedimentary rocks, plant or animal matter gets trapped within the sediments and eventually turns into fossils.

One has to take a note of the fact that these remains are not found in the exact state as they were trapped. Many people wonder why fossils have the same color as the rock. It's because the fossil loses its original color, as several other materials are added to it in course of fossilization.

Though the speed is relatively low, this matter is subjected to decomposition within the sediments itself.

As new layers of sediments continue to form, the pressure induced on the lower layers results in the formation of rocks with fossils trapped inside them. Eventually, these rocks with sediments trapped within them surface owing to some geological process, such as earthquakes or formation of mountains. As this rock comes to the surface of the planet, it is exposed to the agents of erosion, which erode the rock and the fossil within comes to light.

Besides this, fossils are also formed when plant or animal matter is trapped in ice, or when a dead body is subjected to mummification. While fossilization due to freezing is restricted to cold regions, like Antarctica, fossilization by mummification is predominantly observed in dry regions, such as Egypt.