Fossil Record – Chronology of Fossils

Maintenance of Chronological Order and Fossil Record 

 Key Concepts

• Fossils
• Fossil dating
• Chronology of fossils
• Fossil record
• Gaps in fossil record
• Significance of fossil record

Introduction

Fossils are the preserved remains, traces or imprints of any organism that lived in the past. 

Fossils help the scientists to determine various things like approximately when life first appeared on the planet, when animals and plants first lived on land, and also about when the organisms became extinct. 

Fossils tell us the history of life on earth. They help us understand the relationship between organisms, their social behavior, etc.  

They tell us when life first existed on earth. The regional or global distribution of fossils through geological time give us important insights into phenomena such as continental drift, community migration, and climatic reconstruction. 

Explanation

Paleontologists utilize their detective abilities to figure out how old dinosaur fossils or other ancient species are. They can rely on hints provided by distinct rock layers and the fossils found within them. The clues reveal details about the geology, weather, and living forms that existed at the time of each geologic age. To find out the ages of rocks and fossils, two main methods, relative dating and radiometric dating, can be employed alone or in combination. 

Relative dating: 

Relative dating is a method for determining the approximate age of fossils found inside a rock layer. It is based on the concept that newer rock layers are deposited on top of older rock layers in undisturbed environments. Relative dating can only give you an estimate of how old a fossil is. The age of the fossil layer is estimated by comparing the ages of rock strata above and below it.  

Assume a 50-million-year-old rock layer is beneath a fossil and a 35-million-year-old rock layer is above it. The fossil is estimated to be between 35 million and 50 million years old, based on relative dating. 

Absolute dating : 

Absolute dating is the second method of fossil dating and is more accurate than relative dating. Since it uses radioactive elements to determine the age of fossils, it is also known as radioactive dating. 

Using radioactive materials, scientists can get a more accurate estimate of the age of a rock layer.  

As it transitions from a radioactive to a non-radioactive state, a radioactive element emits a constant amount of radiation. The rate at which each radioactive element emits radiation varies.  

Scientists can determine the age of a rock by comparing the amount of radioactive and non-radioactive elements present in it. However, the original amount of radioactive element in the rock can never be calculated with certainty. Hence this method of dating does not always provide exact findings. 

Chronology of fossils: 

Fossils provide a lot of evidence about the evolution pattern and evolutionary relationships. Fossils are also studied by scientists in order to better understand some evolutionary changes and patterns. 

Generally, the rock layer that is older is situated deeper in the Earth. If a paleontologist discovers fossils in a fairly shallow sedimentary rock layer and later discovers others in a deeper sedimentary rock layer, the older fossils are usually in the deeper sedimentary rock layer, as illustrated in Fig. No.4.  

This is true unless the area has been subjected to an extraordinary disturbance that has caused the rock layers to be altered. In this way, the ages of the fossils can be compared by the relative ages of the rocks. 

Fossil record: 

Fossils provide a record of organisms that existed in the past. A fossil record is a collection of fossils that have been studied and placed in taxonomic and chronological order. The sequence in which the events occurred, from first to last, is known as chronological order. All fossils that are discovered and their placements in the formation of rocks and positions in time make up the fossil record. 

Many fields and specialities are used to identify, classify and arrange these fossils, which include comparative anatomy, radiometric dating, and DNA analysis. Scientists aim to recreate phylogenies or trees that describe the links between living and extinct organisms, using data from the fossil record. The fossil record provides insight into how various animal species have evolved over the years. 

Gaps in fossil record: 

It is proof that organisms have evolved over time. However, the fossil record contains gaps, much like a novel with missing pages in a book.  

The gaps exist because of the following reasons: 

1. Most animals die before they can be fossilized: We know that animals are not easily fossilized. This can be due to various reasons like predation by scavengers, unavailability of sedimentary rocks. 

2. Geological processes destroy fossils: Natural calamities like earthquakes, storms, etc., can destroy fossils. The remains of organisms can get damaged or separated because of geological processes. 

3. Fossils have yet to be identified: Only a small percentage of the limited number of lifeforms preserved as fossils have been found and studied by paleontologists. There are a lot of fossils that have not been discovered due to a lack of resources.  

The fossil record shows that the majority of organisms that have ever lived on Earth are Extinct. 

Scientists have concluded that many simpler forms of life existed earlier in Earth’s history, and more sophisticated forms of life appeared later, based on fossil records. Fossils are indeed a form of indirect evidence for evolution on Earth. 

Almost every week, fossil discoveries are made somewhere in the world. When fossils are discovered, they are used by scientists to gain a better understanding of the past. Fossils can be used to create models of what organisms might have looked like in the past. Based on fossils, scientists can sometimes tell whether organisms lived in family groups or alone, what kind of food they ate, or the kind of environment they lived in, and other details. 

Significance of fossil record: 

When fossils are discovered, they are used by scientists to gain a better understanding of the past. Fossils can be used to create models of what organisms might have looked like in the past.  

Based on fossils, scientists can sometimes tell whether organisms lived in family groups or alone, what kind of food they ate, what kind of environment they lived in, and other details.    

The fossil record of whales shows that whales have evolved from coyote-sized semi-aquatic predators, which were thought to live amphibious lifestyles near the shore. 

The fossil record has helped us understand the complete evolution of man. 

Evolution of horses is another example studied by scentists with the help of fossil records. 

Fossils also suggest behavioral patterns of extinct organisms. For example, some dinosaurs used to live in herds. 

Summary

• Fossils are the preserved remains, traces or imprints of any organism that lived in the past.
• Fossils have helped the scientists to determine approximately when life first appeared on the planet, when animals and plants first lived on land, and also about when the organisms became extinct.
• Paleontologists rely on hints provided by distinct rock layers and the fossils found within them to study geology, weather, and living forms that existed at the time of each geologic age.
• Relative dating is one method for determining the approximate age of fossils found inside a rock layer.
• It is based on the concept that in undisturbed environments, newer rock layers are deposited on top of older rock layers.
• In radioactive dating, scientists use radioactive elements in order to obtain a more
  accurate estimate of the age of a rock layer.
• Fossils provide a lot of evidence about the evolution pattern and evolutionary
  relationships.
• The principle of superposition states that when rock layers are undisturbed, the oldest
  rocks are on the bottom, whereas the younger rocks are towards the top.
• A fossil record is a collection of fossils that have been studied and placed in taxonomic
  and chronological order.
• Many fields and specialties are used to identify, classify and arrange these fossils, which
  include comparative anatomy, radiometric dating, and DNA analysis.
• However, the fossil record is incomplete. The gaps exist because most animals die before they can be fossilized, geological processes destroy fossils, or fossils have yet to be identified.
• Despite the gaps, the fossil record shows that the majority of organisms that have ever lived on earth are now extinct.
• Scientists have concluded that many simpler forms of life existed earlier in Earth’s history, and more sophisticated forms of life appeared later, based on fossil records.