A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. Caves can range widely in size, and are formed by various geological processes. These may involve a combination of chemical processes, erosion by water, tectonic forces, microorganisms, pressure, and atmospheric influences. Isotopic dating techniques can be applied to cave sediments, to determine the timescale of the geological events which formed and shaped present-day caves. Speleology is the science of exploration and study of all aspects of caves and the cave environment.