Collecting Fossils – Types, Formation, Significance

Collecting Fossils 

 Key Concepts

• Fossils
• Paleontology
• Types of fossils
• Fossil formation
• Significance of fossils

Introduction

We had learned that there was a time when the earth had a warm, tropical climate all over. Dinosaurs roamed the earth, and giant plants called cycads grew everywhere. Earth’s landmasses formed one huge continent. Today this may sound like science fiction, but it is just a simple description of what scientists call the Mesozoic era in earth’s history. How do scientists determine what earth and its life forms were like millions of years ago? 

Most of the evidence of evolution and the history of life on earth comes from fossils. 

Explanation

A fossil is a remain, a trace or an imprint of an organism that lived a long time ago. Fossils are important as they tell us a story about organisms that lived on the earth before us. Fossils had 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. Fossils are proof of not only when and where organisms once lived but also how they lived.  

Most of the time, the remains of dead plants and animals disappear quickly. This is because when an organism dies, scavengers feed on them and scatter the remains of that dead organism. Later, fungi and bacteria invade and cause the remains to rot and disappear. 

For example, If you’ve ever left a banana on a counter for too long, you’ve seen this process begin. Over time, compounds within the banana cause it to break down chemically and soften. This causes the banana to turn black. Microorganisms further act on it and cause it to decay. 

Paleontology is the study of fossils, and paleontologists are scientists who study fossils. Paleontologists study fossils to determine various evolutionary factors like relationships among different organisms, the approximate time when life first appeared when different organisms lived on earth and also when organisms became extinct. Some paleontologists work outside in the field to discover and then carefully uncover fossils. Paleontologists also work in laboratories analyzing and learning about fossils. 

Types of fossils: 

Imprint fossils:  

A leaf, feather, teeth, bones, or even the entire body of an organism can leave an imprint on sediment that later hardens to become rock. We can say that an imprint fossil is the outline of an animal or a plant that has been left behind inside a rock. They are also known as molds. Molds can be imprints of a shell or the skin of an animal. We have also discovered molds of bite marks, footprints and eggs in a nest. 

Cast fossils:  

Some organisms have hollow structures such as shells, indentions as a part of their bodies. If minerals get filled in these hollow structures of the animal like a shell, gaps or indentions or their footprints, or any other parts of an organism, it creates a cast. A cast is a copy or replica of the original object. 

Frozen fossil: 

Frozen fossils are rare and formed only under special circumstances. They usually date back to the ice age. 

When an organism get stuck, say in mud, pit, tar, etc., and the temperature drops, the remains of the organisms gets trapped in ice and remain frozen for thousands of years. 

Frozen fossils are also known as original material fossils because none of the hard or soft tissues are altered or replaced. The organism is preserved in its original form. 

Frozen remains allow direct study of the actual soft tissues and also sometimes of the organs that make up the animal’s body. They provide more information to the paleontologists. Most of the frozen or original material fossils are more recent than any other type of fossil. 

Fossils in amber:  

Amber is formed when the sticky resin of some cone-bearing plants or trees harden over time. 

It usually contains the remains of small organisms like trapped insects. 

The fossils that get encased in amber probably got there when they came nearby, crawling over or flying in on the fresh seeping sap and eventually got stuck.  

The sap oozed over the stuck animals, trapped them, and then perhaps fell to the ground and later was covered by sediment. The sap later hardened and became a fossil. 

In this type of fossilization, the amber completely surrounds and protects the original material of the insect’s exoskeleton from getting damaged. 

Mineralized fossils: 

Most hard parts of organisms like bones, teeth, and shells have small gaps within them. These gaps can be filled with cells, tissues, blood vessels or air. When the organism dies, and the soft elements inside the hard parts start to decay, the tiny gaps become empty. If the hard part gets buried, groundwater seeps in and deposit minerals in the gaps.  

Fossils are changed by minerals. Mineralized remains are fossils with minerals from groundwater filling the voids inside. They can be petrified or turned into stone. Minerals replace the original tissue or bone in animals or wood in the case of plants to form a piece of petrified wood or a mineralized bone fossil.  

There is a possibility that mineralized remains in the fossil may contain some original material from the organism’s body. It is from these original materials that DNA can sometimes be recovered.  

Often people learn about past forms of life from bones, wood, and other remains that became mineralized or replaced with minerals from groundwater. 

How are fossils formed? 

Most fossils are found in sedimentary rock. Sedimentary rocks are formed when several layers of sand, mud, silt or clay are deposited, compacted and then cemented together, or when minerals are deposited from a solution. Examples of sedimentary rock include limestone, sandstone, and shale. 

Fossils are mostly found in limestone than in any other kind of sedimentary rock. The fossil record acts as evidence to prove that living things have evolved. 

Whether a dead organism becomes a fossil or not depends upon the extent to which it is protected from the scavengers as well as agents of physical destruction, like waves and currents.  

One way to protect a dead organism is for sediment to bury the body swiftly. If a fish dies and sinks to the bottom of a lake, sediment brought into the lake by a stream can cover the fish quickly. As a result, no scavengers or waves can destroy it and tear it apart. The body parts could then be fossilized and incorporated into sedimentary rock, such as shale or limestone. 

However, a quick burial isn’t always sufficient to create a fossil. If an organism has hard parts, such as bones or a shell, it has a better chance of becoming a fossil. This is because scavengers are less likely to eat these hard parts. Hard parts degrade at a slower rate than soft parts. Most fossils comprise the hard parts of organisms, like teeth, bones, etc. 

Why do most fossils include marine organisms? 

Around 99% of all the fossils that we find are of marine animals such as shellfish or sharks. This is because they lived deep inside the sea, where sand or mud could bury their remains quickly after they died. 

The organisms that lived on land were less likely to get fossilized. Most fossils of land animals that have been found were believed to live closer to water bodies. So when the water level rose, their remains got buried in clay or silt. 

Significance of collecting fossils: 

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 insight into phenomena such as continental drift, community migration, and climatic reconstruction. 

Summary

• A fossil is a remain, a trace or an imprint of an organism that lived a long time ago.
  Fossils had 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.
• Paleontology is the study of fossils, and paleontologists are scientists who study fossils.
• Paleontologists study fossils to determine various evolutionary factors like relationships
  among different organisms, the approximate time when life first appeared when different organisms lived on earth and also when organisms became extinct.
• Fossils are found in different forms.
• Imprint fossils consist of a leaf, feather, teeth, bones, or even the entire body of an organism and leave an imprint on sediment that later hardens to become rock.
• Cast fossils are formed when minerals get filled in the hollow structures of organisms and create a cast.
• Frozen fossils are formed when organisms become trapped, and the temperature drops, so the remains of the organisms get stuck in the ice that remains frozen for thousands of
  years.
• When organisms get encased in amber, they form amber fossils.
• In mineralized fossils, fossils are changed by minerals. They can be petrified or turned
  into stone.
• Most fossils are found in sedimentary rock.
• Sedimentary rocks are formed when several layers of sand, mud, silt or clay are deposited, compacted and then cemented together, or when minerals are deposited from a solution.
• If an organism has hard parts, such as bones or a shell, it has a better chance of becoming a fossil.
• Around 99% of all the fossils that we find are of marine animals because they lived in the sea, where sand or mud could bury their remains quickly after they died.
• The regional or global distribution of fossils through geological time give us important insight into phenomena such as continental drift, community migration, and climatic reconstruction.