Earth sciences, the fields of study concerned with the solid Earth, its waters, and the air that envelops it. Included are the geologic, hydrologic, and atmospheric sciences. The broad aim of the Earth sciences is to understand the present features and past evolution of Earth and to use this knowledge, where appropriate, for the benefit of humankind. Thus, the basic concerns of the Earth scientist are to observe, describe, and classify all the features of Earth, whether characteristic or not, to generate hypotheses with which to explain their presence and their development, and to devise means of checking opposing ideas for their relative validity. In this way the most plausible, acceptable, and long-lasting ideas are developed. The physical environment in which humans live includes not only the immediate surface of the solid Earth but also the ground beneath it and the water.