How old is Earth? How old are the planets, the Moon, meteorites, stars, and the Universe itself? How do scientists know these things? If you've ever asked yourself some or all of these questions, then this book is for you. Planet Earth and the other bodies of the Solar System are 4.5 billion years old. They reside in a galaxy (the Milky Way Galaxy) that is 12-14 billion years old, and are part of a universe that is 13-15 billion years old. G. Brent Dalrymple, a geologist and widely recognized expert on the age of Earth, reviews the evidence that has led scientists to these conclusions and describes the methods by which this evidence has been gathered. The book is written in a highly accessible style, free of mathematics and complex graphs, and is intended for non-scientists who have an interest in the subject. People with scientific backgrounds who wish to have a thorough summary of the subject will also find the book useful.