Many mysteries still cloak many phenomena of our Earth. When we look at geophysical phenomena on the basis of deuterium nuclear reactions, novel findings cast new light on the many unresolved problems. Indeed, there are many unanswered questions regarding the cause and source of the heat released from Earth’s interior, the reason for the high composition of nitrogen in the atmosphere, the helium paradox, and the creation of elements. However, as this book shows, these behaviours could be explained by nuclear fusion and transformation. Furthermore, it is suggested here that deuteron nuclear fusion is possible in the cores of Earth, Jupiter, and Saturn, as well as the coldest brown dwarf. Our Earth is now on the point of dying from warmth, the activation of magma, and pollution. This book will help solve these problems. Mikio Fukuhara retired from the New Industry Creation Hatchery Center of Tohoku University, Japan, in March 2018, and is now a Research Fellow at the same institution. His current research interests are focused on nuclear geoscience and quantum supercapacitors of amorphous oxide and carbon neutral cellulose.