Index fossils play an important role in science particularly in its branches called geology and paleontology. They are used to identify the approximate age of another fossils. This technique is known as relative dating which allows geologists as well as paleontologists to determine the fossil age through scrutinizing the relationship of that certain fossil with another event of a specific period.
What are Index Fossils?
An index fossil is also known as an indicator fossil, zone fossil or a guide fossil. Its main job is to help resolve the faunal stage or geological period. These fossils are quite abundant on Earth since they are commonly found and widely distributed though restricted in time span. To make it much easier to understand, these fossils are simply remains of plants and animals preserved inside the rock layers of our planet.
These index fossils date back to a definite geological time. They are essentially easy to identify and are currently utilized by experts as a guide or standard of their period. This is because of their bountiful numbers and circulation geographically.
As you may already know, a fossil is any trace or remains of an ancient organism that has existed on Earth. Once a creature becomes a fossil it has undergone a particular process known as fossilization. This is a very rare process in that only a tiny percentage of organisms ever become a fossil. This is because most of the carcasses found on land get eaten by scavengers and the leftovers are consumed by insects. On the ocean floor, they quickly decay or are scattered away which is a natural occurrence.
Use and Significance of Index Fossils
Because of the index fossils and the other forms of fossils, it is clear that life on our planet has changed over time. Paleontology, which is the study of prehistoric life on Earth surely benefits from index fossils. Geology can also get all the help it needs with this type of fossil in order to understand what the Earth is comprised of including the rudiments surrounding our planet as well.
With index fossils, it is much easier to define the boundaries of time scale with respect to the strata where the fossils are discovered. The US Geological Survey or USGS affirms that these fossils are being used as guides in order for them to successfully estimate the age range of the rocks when they are revealed. Once the date of the rocks has been determined using the index fossils, the rocks are then studied to help determine the period when the fossils were created.
Moreover, they help in figuring out the date for other fossils that are found within the same sedimentary layer. For instance, if a geologist finds a fossil coming from an unknown era, he will turn to another fossil which can be dated to a certain period of time. Then he can assume that these two species belong to a relative era.
Index fossils are important to date and understand geological formations. They allow scientists to gain insight with regard to our planet’s environment along with the life forms that inhabited the Earth even as far as hundreds of millions of years ago. Geologists collect fossils from various rock formations and layers and have discovered that the assemblage of these index fossils help them recognize the layer of rock in which they were found in.
Examples of Index Fossils
In general, there are three different eras in which the types of index fossils are classified into. The first one is the Cenozoic Era. The ones that belong in this group are commonly known as recent fossils. In this period, the fossils discovered during the Quaternary period including the Pecten gibbus or the Argopecten gibbus and Neptunea tabulate comprise this group. The Quaternary period goes 1.8 million years back. The ones found in the Tertiary period like the Venericardia planicosta and the Calyptraphorus velatus represent this collection as well. Pecten gibbus fossils are actually comparable to the seashells that we find on many beaches today.
The second classified era of index fossils is the Mesozoic Period which is referred to as the age of medieval life. Fossils originating in this period such as the Inoceramus labiatus and the Scaphites hippocrepia were both found during the Cretaceous age. The Jurassic period also belongs to this classification to include fossils such as the Nerinea trinodosa and the Perisphinctes tiziani. Finally, the Triassic period includes the Monotis subcircularis and the Trophites subbullatus. The ammonite fossil which is probably the most commonly-known fossil type today is found during the Mesozoic era.
Ammonites are extinct invertebrate animals that used to live underwater. These mollusks are considered excellent index fossils because they provide a huge possibility of linking a rock layer to a certain geological time. This is one reason why they are widely used for determining fossil and rock age.
Finally, the last type of fossil comes from the Paleozoic era which is also known as the ancient life. Permian fossils like the Parafusulina bosei and the Leptodus americanus were discovered during the Permian period during the Paleozoic era. Another is the Pennsylvanian period when the Lophophyllidium proliferum and the Dictyoclostus americanus fossils were found. The Devonian period includes fossils namely the Palmatolepis unicornis and the Mucrospirifer mucronatus while the Mississipian period has the Prolecanites gurleyi and the Cactocrinus multibrachiatus.
Also included in this group are the Tetragraptus fructicosus and the Bathyurus extans which are both from the Ordovician period. The Silurian period includes the Hexamoceras hertzeri and the Cystiphyllum niagarense. During the Cambrian period, fossils like the Billingsella corrungata and the Paradoxides pinus were discovered. Trilobites comprise the most part of Paleozoic fossils. They were discovered 245-540 million years ago. These index fossils are invertebrates that inhabited marine life. They had hard exoskeletons but went extinct around 250 millions of years ago approximately during the Permian period.
It is not a secret that fossil records are incomplete. We still have so many things to learn about what happened millions of years ago. Prehistoric life is still puzzling to scientists particularly paleontologists. However, we can at least give thanks to index fossils because they help in organizing the fossil records. These distinctive relics serve quite a significant purpose in science.