Chapter 26.5, Problem 8SAQ

Summary Introduction

To describe:

The environmental changes recorded by the sedimentary rocks that contain the oldest fossils of large active animals.

Introduction:

The fossils are the old conserved remains found in the rocks. The oldest rocks contain the fossil records of the earliest organisms, while the fossil remains of newly evolved organisms are complex as compared to that of simple organisms. The evolution can be studied with the help of fossil records.

Explanation of Solution

In the atmosphere and surface of the oceans, the oxygen started to concentrate nearly about $\text{2400 million years ago}$. The oxygen level in the atmosphere remains very low over a long time period.

The formation of the multicellular organisms started approximately 580-560 $\text{million years ago}$. The fossils of these multicellular organisms showed the presence of increased levels of oxygen in the atmosphere because they were aerobic organisms.

Conclusion

This shows that the abundant oxygen started to accumulate nearly about 580-560 $\text{million years ago}$. The study of fossils in sedimentary rocks helped in determining the evolution of multicellular organisms and increased levels of oxygen.