By Cosme Moran Paz
Mold Fossils
These are fossilized imprints that are made within a substrate. The substrate, in this case, is usually a rock or sediment. The fossil makes use of these substrate components in order to leave their mark on them. A mold fossil is kind of like an impression that is made in the substrate. They are quite similar to the negative impressions left by an animal or a plant. Mold fossils are primarily formed through a process called ‘leaching.’ In this process, the shell material of rock, for instance, is removed, leaving behind a hollow or gap in the rock.
Unlike cast fossils, mold fossils are more towards the hollow end, which is one of the reasons why the end or resulting image is more like a negative image or impression of the organism’s body part.
Cast Fossils
These are a result of the mold fossils when the latter gets filled with some kind of minerals. What happens here is that when mold fossils are formed, there are times when their hollowness is filled with certain kinds of minerals. Over time, these minerals begin to harden, and in doing so, they tend to form an exact replica or model of the original fossil that was there in the first place. This replica is what we call a cast fossil. In other words, when a plant, animal, or any other organism dies, certain chemical reactions take place in its remains that lead to a deterioration of bones and great flesh decay. Both these things create a gap or hollow in the organism, more like a cavity that is eventually filled up minerals found in the underground. When these minerals harden over the passage of time, they create a ‘cast’ which is what gave these fossils their respective name. Cast fossils leave an imprint in the rock or sediment and go a single step further than the mold fossils.
Trace Fossils
These fossils are also called ‘ichnofossils,’ and they contain any potential information or traces left behind by the organism. They are basically glimpses that let us know how the particular organism behaved and what its activities were like when it was alive. These fossils are more like indirect evidence of the existence of the prehistoric life. There are different types of trace fossils that can be grouped together into various categories. These types include: ● coprolites ● tracks and trails ● gastroliths and burrows ● borings. All these types of trace fossils help archaeologists decipher the happenings and the activities of the past life. The thing with trace fossils is that they often end up separating themselves from the organism that originally formed or created them. This makes it really difficult for researchers and scientists to figure out which specific organism and its habitat and activities resulted in the formation of a particular trace fossil.
Petrified Fossils
Petrifaction is a process in which things turn into stones, and petrified fossils are those that are formed when minerals from the underground replace certain or all parts of numerous organisms. Since water is often fully enriched with dissolved minerals, it easily reaches the dead organisms by seeping through the layers and cracks of rocks or sediments. Once this mineral-rich water evaporates, it leaves behind the stone, hardened materials and minerals. Petrifaction turns living organic materials into stone, and this process essentially takes place when the molecules found within an organism are properly replaced by those molecules of the water minerals.
There are numerous types of petrified fossils, among which petrified wood is the most common type. Another type is teeth and bone, but these are less common as compared to petrified wood mainly because they end up decomposing really quickly and easily. Petrified fossils have served far greater purposes than just in terms of their importance and value. Scientists have used information from these fossils and found a link to phylogeny, a study of how organisms are connected to evolution. This allowed these scientists to determine how some species are related to each other. With respect to the organisms found contained within the petrified fossils, scientists could understand and explain the numerous ways in which the adaptation process has caused so many species to either greatly evolve, or simply become extinct.
Carbon Film Fossils
It is a very common fact that all living organisms contain an element of carbon in their body. So, when a dead organism lays on a rock and is deeply buried inside sediment, a thin layer of this carbon is left behind and deposited onto the rock over the passage of time, and simultaneously, all the material found within the organism gradually breaks down. This thin carbon layer basically reveals the respective organism’s delicate parts, for instance, leaves from a plant that probably lived millions of years ago. This happens because the oxygen, hydrogen, and nitrogen disappear from the organism’s body and end up either being dissolved or vaporized under the water body. Unlike petrified fossils that create a three-dimensional cast, carbon film fossils create a two-dimensional image that is well-imprinted into the rock or sediment. These films also greatly stand out from the rock since they have a very prominent black or brown color. The most common types of carbon film fossils are leaves, fish and crustaceans, primarily because the specimens that are preserved under the water body are the only ones that leave behind carbon films.
Preserved Remains The process of fossilization often preserves the whole of an organism; however, there are also times when it preserves only a part of the organism with very little change. Such organisms are conserved in or very close to their original states. They are the ones that are called preserved remains fossils and are incredibly similar to the true form fossils. Preserved fossils are a very rare occurrence, considering how most fossils end up suffering a great amount of damage due to various processes like sedimentation and weathering way before these fossils are even discovered. In amber, what really happens is the organic matter, be it an insect or a leaf, gets surrounded by a natural tree resin. Over time, this protective cover or layer preserving the matter hardens and becomes stone-like. Amber is also referred to as a gold-colored resin that originally comes from the pine tree sap. Another way of remains being preserved without alteration includes being frozen in ice. Many organisms die in intensely cold regions, after which their bodies are frozen in ice and even something as small as their strands of hair gets preserved in the ice. A great example of this is the preservation of the woolly mammoth that was extinct for thousands of years. It was discovered in the Siberian Glaciers where it was found frozen under huge blocks of ice.
index fossil
Index fossil, any animal or plant preserved in the Earth's rocky record that is characteristic of a particular period of geologic time or environment. A useful index fossil should be distinctive or easily recognizable, abundant, and have a wide geographic distribution and short range through time. Index fossils are the basis for defining boundaries on the geologic time scale and for strata correlation. In marine strata, commonly used index fossils include the single-celled Protists with hard body parts and larger forms such as ammonoids. In terrestrial sediments from the Cenozoic Era, which began about 65.5 million years ago, mammals are widely used to date deposits. All of these animal forms have hard body parts, such as shells, bones, and teeth, and they evolved rapidly.
Body Fossils These are easily the most common and popular types of fossils found all over the world. As the name evidently suggests, body fossils are formed from the remains of dead plants and animals. These are usually hard parts of an organism including shells, bones, teeth, woody trunk, stems, and branches. Whole-body fossils are the complete remains of organisms belonging to the prehistoric times. These also often include the soft tissue of organisms, for example, insects that get trapped inside tree sap and then harden down to create amber.
Soft tissue like skin, organs, and muscle usually fall to pieces once the organism dies, leaving behind only the bone skeleton and the hard shells of all those organisms. The most common types of body fossils include teeth, bones, and claws. Bones have by far been the most vital body fossil to learn about dinosaurs. The fossilized bones of numerous dinosaur species have been found since ancient times and in 1818, the first-ever dinosaur bone was discovered. These are the remains of actual organisms while their hard skeleton is preserved and kept intact even after millions of years.
Summary Fossils in my understanding are organisms which lived many years ago or a few years ago, these organisms often remain or survive preserved by different ways, which are the following: ● A mold fossil: this is a type of fossilization that is depressed from the body of the organism most commonly in rocks through a process called 'leaching' ● Cast Fossils: This fossil is usually the product of the mold fossil because when the hole is in the rock or object it is usually filled with different minerals within which they create a replica or copy of the original social thanks to the mold. ● Trace Fossils: yes, this type of easy could tell us some important characteristics about the life of the organism thanks to its footprints we can know a little about what it was doing when it was alive. ● Petrified Fossils: This type of fossil involves a process which makes organisms turn into stone thanks to a process that involves various minerals. ● Carbon Film Fossils: this type of fossil is like an implementation of the real fossil, but only its surface is imprinted on the rocks thanks to the fact that all organisms have carbon inside their body. ● Preserved Remains: This is an incredible process which leads to preserve most of the body of the organism and they are very useful to study the organism of the living being. ● Index fossil: itself is a record which bears the characteristics of the time period in which the fossil was found. ● Body Fossils: These are the types of fossils which are the most found. All these different types help us to understand the past of these past species, as well as how they lived and in the conditions that the planet was in.
References
9 Different Types of Fossils:https://nayturr.com/ty pes-of-fossils/ https://www.britannica.com/s cience/index-fossil