Many geologists classify a landform as a mountain if it is at least 300 meters or more above its surrounding topography. Mountains have steep sloping sides, rounded or sharp ridges, and a peak or summit. Hills are not as... More »

Rocks are important because geologists use evidence from them to learn about what the Earth was like in the past. They allow scientists to build a historical record of the planet to learn what events occurred before peop... More »

Some famous geologists in history include Eratosthenes, James Hutton, Sir Charles Lyell, Mary Anning and Alfred Wegener. Others include Gene Shoemaker, William Smith, Friedrich Mohs and Inge Lehmann. More » Science Earth Science Geology

As of 2014, geologists contend that granite is a plutonic rock resulting from deeply buried shale and sandstone that melted, partially melted or metamorphosed, depending on the category of granite in question. Igneous gr... More » Science Earth Science Geology

The principle of original horizontality refers to an assumption by geologists that all layers of sedimentary rock were horizontal when they were formed. This is one of the basic principles of stratigraphic succession, wh... More »

More than any other type of fossil, index fossils define geological time periods for geologists by providing the most useful information about the age of the rock they are found in. Index fossils are also called key foss... More »

The fossil record refers to the collection of physical and research evidence that paleontologists and geologists have used to prove the veracity of evolutionary theory. The physical evidence in the fossil record comes fr... More »