Earth younger sedimentary rocks

These stratified layers are like pages in the ultimate history book—Earth s history— where each page is dedicated to a particular time frame, earliest to present. Sediments of any particular time period form a distinct layer that is underlain and overlain by equally distinct layers of older and younger times, respectively. These layers, composed of such common rock types as sandstone, shale, and limestone, make up about 75% of the rocks exposed on the surface of the Earth. Geologists can study sedimentary rocks in the making therefore, they probably know more about the origin of this type of rock than igneous and metamorphic rocks combined. 

---