It turns out the answers are in Earth's rocks. Even the Greeks and Romans realized that layers of sediment in rock signified old age. But it wasn't until the late 1700s -- when Scottish geologist ...

Over time, the layers are compressed and glued together.Metamorphic rocks are formed from other rocks, igneous or sedimentary, which are heated and compressed underground.Igneous rocks are formed ...

If you were to slice through it, you would see the Earth is divided into distinct layers. On top is the relatively thin crust where we live. Beneath that is the 2,900 km thick mantle layer.

John Wesley Powell had more than just a passing interest in the layers upon layers of rocks exposed by the Colorado River. The expedition down the Green and Colorado Rivers, he would later claim ...