Geology is the Scientific study of the Planet Earth. Mainly geology is about Rocks but geology includes study of oceans, soil erosion etc. Geologists also study the hot mantle deep within the Earth which is part solid and part liquid. Geology studies the even hotter core of the Earth which generates electric currents and causes the Earth's magnetic field. Geology covers everything below the earth's surface.
Geology can get quite upsetting for Creationists and especially Young Earth Creationists because within many sedimentary rocks there are fossils of plants and animals that lived long ago and were buried by silts, sands and other deposits. These fossils, along with signs of past landforms such as annual layers in sediments, are evidence both that the Earth is far older than some religions say, and also that species have evolved over time - this upsets some religious people who believe that we were created by God in his image.
Not to mention, geologic scientists have concluded that the Earth is 4.54 billion years old, and after that discovery, the Young Earth Creationist community had the world's biggest hissy fit.
Geologists have also produced evidence that the Earth's climate and atmosphere have been very different in the past, and how rapidly it can change. This evidence tends to be ignored or simply not accepted by petrolheads who would rather deny a problem like Global warming than try and solve it.
Many geologists work for oil and mining companies and are employed to predict where to mine for natural resources such as metals and hydrocarbons, and also how large our unexploited reserves are; Or they are employed by waste disposal and other polluting companies to predict how confident we can be that pollution won't get into our air or water if we bury nuclear or other waste in particular locations. Other geologists have worked for Academic and environmental organisations and have challenged some of the commercial estimates
Geologists and physical geographers have produced a lot of information about natural disasters, ranging from Asteroid/Comet strikes to Earthquakes, Tsunami and volcanic eruptions. Politicians are beginning to listen to some of this information, especially where stuff can be quantified in terms of a measurable risk that may well happen within the Politician's career. The political process tends to handle other risks worse ie risks of the one in a thousand years or less nature.