Because Earth Science is so broad, it is often best to take a systems approach to studying it. In a systems approach, one considers separate spheres of influence that all impact one another. There are often many positive and negative feedback processes as different components interact with each other.
Earth System Science in particular, looks at spheres of influence defined by different parts of the earth and how common materials cycle between them. The most common cycles to study are the carbon, nitrogen, phosphorous, oxygen, water, and energy cycles. The primary three spheres are the lithosphere, the atmosphere, and the hydrosphere; though sometimes a fourth sphere - The cryosphere - is also considered. The earth as a whole can be considered as a geosphere, comprised of these individual spheres.
A visual representation of the spheres could look something like this:
A brief description of each of the primary spheres making-up the geosphere follows below:
1) The lithosphere - The lithosphere is the mostly solid material making-up the earth itself. This includes rocks, minerals, landforms, bedrock, and the inside of the earth. The sciences of geology, mineralogy, and seismology focus on this sphere.
2) The atmosphere - The atmosphere is the bubble of gas surrounding the planet. This includes the sky, the clouds, the wind, and the air we breathe. Weather largely takes place in this sphere; though its impacts on the others are quite significant. The sciences of meteorology, atmospheric science, and climatology focus on this sphere.
3) The hydrosphere - The hydrosphere is the liquid water on the earth. This includes the rivers, lakes, streams, and oceans. The sciences of oceanography, hydrology, and marine science focus on this sphere.
4) The cryosphere - The cryosphere consists of the frozen earth. It includes the polar ice caps, ice sheets, glaciers, and anywhere ice is found. It also includes regions of permafrost. When this sphere is not considered separately, the ice is included in the hydrosphere.
It is common in earth system science to also examine the interactions between these spheres and one additional sphere - the biosphere. The biosphere is everything living on or in the earth. This includes plants, animals, bacteria, fungi, and protists. The sciences of biology, botany, and zoology focus on this sphere.
When visually representing the spheres of influence, The biosphere is often placed in the center of diagrams with the other three cycles surrounding it, as seen in the diagram below. This placement is because life is found inside each of the other spheres.
In other diagrams, like the one seen below, the biosphere may be placed off to the side completely. This placement is because the biosphere isn't a physical part of the earth, or the geosphere, as the other spheres are.
Several Colleges and Universities including Penn State, UCLA at Irvine, and University of Alabama have Earth System Science departments and degree programs.
The Journal of Earth Systems Science is one of a few peer-reviewed scientific journals dedicated to the topic, and a good source for research.