Ife on Earth has a rich history nearly 3.5 billion years in duration. For more than half that time, this planet was dominated by tiny, inconspicuous, single-celled archaebacteria and eubacteria. Close to 2 billion years ago, more complex multicellular organisms appeared, and in the last half billion years or so, their descendants proliferated into a bewildering array of creatures.
If we continue using the metaphor of the Earth’s stratigraphic layers as “pages” in a book, then fossils, like this fossil fish from Cretaceous strata of Liaoning, China, are the “illustrations” that help us visualize this planet’s biologic changes. Fossils not only provide us with direct insight into the evolution of life, they also provide hints about interactions among life forms and about the environments in which they lived. Animals, plants, and other organisms are sensitive indicators of changing habitat conditions. The distribution of life forms can tell us about climate history, sea level position, oxygen levels, consistency of the sediment, and other things.
To understand the fossil record, we first need to review what life forms dwell on Earth today, review their ecology, and then project backward in time. Some organisms have changed little since they first evolved, and others have undergone astonishing transformations.
In this chapter, you will be introduced to life forms, how they are classified, and how and where they live. Then you will discover how life forms have left a record of their existence as fossils and how a community of living organisms translates to an assemblage of fossils. You will learn what organisms have the highest odds of success in the fossilization process and what environments tend to favor the preservation of fossils.
World History
