Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
Foundational Concepts
Foundational Concepts
Dating Methods
Earth Processes
Life Processes
Studying the History of Life
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Introduction to Biological Processes

The physical and biological processes that take place on Earth are interrelated. The physical changes that shape the planet also affect its living organisms. This link has been documented throughout Earth history, and we see evidence of it even today. For example, animals and plants display obvious adaptations to particular climates and environments, as in the cacti of the deserts of western North America or the streamlined bodies of fish, whales, and dolphins. Less well appreciated is the fact that living organisms can alter the physical Earth as well. One such example is the “oxygen crisis” that occurred some two billion years ago, when newly evolved photosynthetic organisms produced oxygen in sufficient quantities to permanently change Earth’s atmosphere. Clearly, it is not possible to understand the histories of life and of the Earth as separate stories. Therefore, although this section focuses on the biological processes associated with living organisms, many of these processes have explicit connections to geological processes as well.

Let’s begin with an introduction to the basic qualities of life itself, including its origin. The basic structures of living organisms form the building blocks for all subsequent biological processes. Once life appeared on the early Earth, the challenges presented by the physical environment immediately began driving the process of evolution, which continues unceasingly today. Evolution is a multifaceted process and is, perhaps, the most important process in the history of life. Extinction also plays an important role in shaping the history of life, eliminating even dominant species and reshaping the nature of the biological world. Both evolution and extinction occur in the context of ecology—the study of the relationships between organisms and the environment.

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