When a geoscientist mentions Cretaceous we know that this time occurred between 65 to 144 million years ago. Uniformitarianism is an important theory central to understanding in geology and geomorphology. This theory suggests that the continuing uniformity of existing geomorphic and geologic processes should be used as the intellectual framework for understanding the geologic history of the Earth. Igneous rocks are formed by the solidification of magma. This solidification can occur at or beneath the Earth's surface.
Sedimentary rocks develop from the lithification of sediments or weather rock debris.
Metamorphic rocks are created by the alteration of existing rocks by intense heat or pressure. Most rocks are composed of one or more minerals. A mineral can be defined as a naturally occurring inorganic solid with a crystalline structure and a specific chemical composition. Over 2000 different types of minerals have been classified. Each one of these minerals is composed of one or more chemical elements.