The study of geography looks first at the physical planet Earth, including landforms, the makeup of different layers of the Earth, the oceans, climate, and the lifeforms that exist in different geographic regions. Geographers might study the ways in which the Mississippi River has changed, for example, by looking at the layers of rock and soil that have been eroded away or by measuring the distance between river banks to appreciate how the level of water in the river has decreased over time.
Human ecology is concerned with the relationships between humans and other forms of life, and with how those relationships impact the environment. Human ecology addresses issues such as pollution, depletion of natural resources, overpopulation, endangered species, and more. Human ecologists might analyze changes in water quality in the Mississippi River, looking at how those changes are impacted by industrialization and/or shipping on the river and at how the changes are affecting the plants and animals that live in or near the river.