Modern humans have been on Earth an estimated 200,000 years, and during that time we’ve worked relentlessly to understand the inner workings and history of our 4.5 billion-year-old home planet. Geologists study rock formations from the surface to deep in the Earth’s crust. Volcanoes, hydrology, weather, and biological activity have all profoundly affected the structure of the Earth’s land masses and oceans, and by studying these effects, geologists can learn about the Earth’s distant past and use the information to make educated predictions about the planet’s future. The epic scale of geologic research makes it an appealing academic subject and career path. This list features sites from every stratum of the online geological community, and they are not being ranked or rated.