The study of life in our universe has been given the name 'astrobiology'. It is a relatively new subject, but not a new discipline since it brings together several mature fields of science including astronomy, geology, biology, and climatology. An understanding of the singular conditions that allowed the only example of life that we know exists to emerge and survive on our turbulent planet is essential if we are to seek answers to two fundamental questions facing humanity: will life (and especially human life) continue on Earth, and does life exist elsewhere in the universe? Astrobiology of Earth adopts a unique approach that differs from most texts in the field which focus on the possibility of extraterrestrial life. In contrast, the central theme of this book is the fortuitous combination of numerous cosmic factors that together produced the special environment which enabled the emergence, persistence and evolution of life on our own planet, culminating in humanity. This environment has been subject to constant and chaotic change during life's 3.6 billion year history. The geologically very recent appearance of humans and their effect on the biosphere is discussed in relation to its deterioration as well as climate change. The search for extraterrestrial life is considered with a view to the suggestion that humans may escape a depleted Earth by colonizing the universe. This book contributes to our understanding of astrobiology from the perspective of life on Earth and especially human welfare and survival. Astronomical and geological phenomena are related in turn to their biological relevance and impact. This introductory text assumes little or no prior knowledge of more specialized scientific fields and is designed for undergraduate and graduate level students taking related courses in departments of biology, earth science/geology, and environmental science. It will also serve as a useful biology primer for astronomy majors.