Fossils: Where are Fossils Found?

key Concepts

• Occurrence of fossils
• Formation of fossils

Introduction: 

A landscape is all the visible features such as mountains, hills etc. on the Earth’s surface present now or in the past. Earth’s landscape from the past can be learned by studying rock layers and the fossils found in those layers. Earth’s history can be studied by seeing the layers of the Earth. The upper layer of the Earth are new layers, and the bottom layers are old layers. In sedimentary rock, it is very easy to see the layers of the rock because sedimentary rocks are formed by the accumulation of layers on each other. It is easy to see the geological history of the Earth in areas where such types of sedimentary rocks are present. 

The Grand Canyon is the best example where we can see the Earth’s surface was carved by the Colorado River. This is due to the weathering of rocks by water. In Grand Canyon, many layers of sedimentary rock form the high walls of the canyon. The walls show a history of the Earth’s surface that dates back to about 2 billion years. 

Age of the rock:

Geologist think that the Earth is about 4.6 billion years old. It is very diificult to find out the age of the rock. Fossils, found in various rock layers, help scientist to find out the age of the rock. Relative age or relative dating shows that one layer is older or newer than the other layer but cannot show the age of rock in particular years. To determine the relative age of rocks, scientist generally study the layers present in sedimentary rocks. To learn about Earth’s history, scientist generally need to find the numeric age of a rock formation or absolute age or absolute dating of a rock formation. For example, the age of an igneous rock is the time it solidified from molten rock.  

Scientist use geological processes that can be observed or measured over a period of time, or chemical composition of rock. Study of rate of erosion, calculation of rate of sediment deposition can also help to estimate the absolute age of a rock. 

The fossil record: 

The remains of plants or animals that lived in a previous geological time and are buried in sediments such as sand, mud, lakes, oceans are called fossils. Fossils give clues about earlier geological events, climates, and the evolution of living things over a period of time. Paleontology is the study of fossils. 

Fossils of marine plants and animals gives us the information about the areas that were covered by oceans in the past. This information helps the scientists to learn about the effect of changes in the environment on the living things. 

Formation of fossils: 

Fossils are formed from hardened tree sap (known as amber) where insects get trapped in sticky sap and are preserved when sap is hardened. Organisms buried in frozen soil or ice do not decay and form fossils. Carbon residue of leaves, stems, flowers, and fish found preserved in sedimentary rock made of soft clay and mud. Stones present in the digestive system of dinosaurs called as gastroliths remain as fossils.  

Types of fossils:

Fossils give lots of information about ancient organisms. Trace fossils provide the information and evidence of past animal movement such as burrows, footprints, borings and tracks and prehistoric life. Footprint of an animal gives the clue about the animal’s appearance and activities.  

Proper ordered arrangements of rock layers is known as geological column. It shows the timeline of Earth’s history where oldest rocks are placed at the bottom of the column and new rocks are placed at the top of the column. 

Summary

• A landscape is all visible features such as mountains, hills etc. on the Earth’s surface present now or in the past.
• Relative dating means study of rocks and fossils to understand which ones older and which ones are younger.
• Absolute dating means to find out the actual ages of rocks or fossils, Le, the year at which they were formed.
• Study of rate of erosion, calculation of rate of sediment deposition can also help to estimate the absolute age of a rock.
• Fossils give lots of information about ancient organisms.
• Proper ordered arrangements of rock layers is known as geological column.