What are some overlaps of the Environmental Science and Geology fields?
Environmental science is a highly multidisciplinary study of the environment, the surroundings of living and non-living things. It accommodates areas such as meteorology and weather systems, ecology, zoology, atmospheric physics & chemistry, mineralogy and oceanology. It is a study largely of figuratively and literally fluid things, such as habitats, which change all the time, the atmosphere, and weather.
Geology is more solidly based. It is the study of the hard matter on Earth, things which take many years to give a hint of change (most of the time). Rocks are essentially the major focus of geology, though it incorporates other areas, such as organic matter in the Earth like oil and fossils.
The two cross over where geological processes become relevant to the environment, or where the environment becomes relevant to geological processes. In the former, tectonic and volcanic activity may release copious amounts of fumes, ashes and molten rock, which can affect habitats, weather systems and climate change as a whole via the greenhouse effect. Being able to predict when an eruption may occur and how devastating it will be is important to environmental scientists as much as it is to geologists and neighbouring villages.
We can also predict what the atmosphere may have been like in its developing stages based on geological activity. Volcanoes finally stop releasing fumes, water vapour settling into oceans as the atmosphere cools, and somewhere along the line there are just the right conditions for life to emerge (according to one belief system, of course).
Both geology and environmental science come under the category of Earth science, and the distinction between them is really arbitrary, as each requires the other for a complete understanding of Earth as a dynamic system. They overlap when the processes described by each interfere with the other, such as in erosion or volcanoes or soil science.