The Earth's integrated system of atmosphere, hydrosphere, and biosphere is driven by the energy of solar radiation just as we are, and even the system of the solid Earth (lithosphere) is driven by the decay energy of radioactive elements in the Earth. The boundary region between these four spheres is called the Geosphere, and these four spheres interact through the circulation of energy and materials. A huge variety of episodes has occurred and evolved in the Geosphere during the long history of the Earth, and we human beings are the newest product of this sphere. Our Department of Geoenvironmental Science is pursuing changes in the past, present, and future of the Geosphere's environment from ancient rocks and sediments through current knowledge of physics, chemistry and biology, which are not yet fully understood only by using today's observational research, from the viewpoint that they are snapshots of the evolving Geosphere. Our Department is coming to a better understanding of the Earth's environmental system because current human activities are having serious consequences on the Earth's environment.