They have been slowly recycled over millions of years.This is called the rock cycle.Sedimentary rocks form when tiny particles of rock that have been weathered and eroded settle out of slow moving ...

"Sedimentary rocks are principally composed ... recycled and transformed by geological processes is known as the rock cycle. Some rocks are mono-mineralic, meaning they only contain one mineral.

New research into fossilized rock formations in Zimbabwe is shedding light on Earth's nitrogen cycle before the rise ... nitrogen isotope values found in sedimentary rocks dating back 2.75 billion ...