Biological evolution began when cells formed

About 3.8 billion years ago, interacting systems of molecules came to be enclosed in compartments. Within those units— cells—control was exerted over the entrance, retention, and exit of molecules, as well as over the chemical reactions taking place. The origin of cells marked the beginning of bio-

Each "day" represents about 150 million years.

Life appeared some time during "days" 3-4, or about 4 billion years ago.

r l Earth \ forms

Ortyn of life l Earth \ forms

Ortyn of life




9 \


11 \


1 \ Oldest 1 1 1 fossils 1


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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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