Written human history only dates back a few thousand years. The Earth is considerably older than the human race, and had gone through countless momentous events and changes long before humans arrived. Historical geology studies rock, mineral and geological formations to give modern humans a better picture of ancient history on Earth. Making use of modern technology such as radio carbon dating, historical geology teaches humans about the past, and may even give a glimpse into the future behavior of the planet.
Determining the age of rocks is an important part of historical geology. In the 19th century, the work of several prominent scientists brought the concept of radioactivity to light. More recent discoveries have shown that certain radioactive elements break down at a predictable rate into a more stable element form. By measuring a rock sample for the amount of the original element and its broken-down version, geologists can now get a fairly accurate idea of the age of the sample. Using radiometric dating, historical geology has made confident estimates not only about the age of rocks, but the age of the planet itself.
Sedimentary rocks are of great importance in historical geology and related fields of ancient history. Sedimentary rocks occur through compression of sediments over time, such as dirt, sand, and organisms. Much of science's fossil information comes from bones and skeletons embedded in sedimentary rocks. Historical geology can tell much about former species and extinction by examining fossils and surrounding rock. Sedimentary rocks can also give considerable information about past climates, as sediments will wear down differently depending on the atmosphere around them.
Historical geology does not only give clues to the past, it can also formulate understanding about the geological makeup of the present. Mining businesses and companies that search for oil and natural gas reserves often employ geologists that study historical geology. Understanding a region's past can greatly contribute to understanding the likelihood of certain substances or minerals in the present.
For centuries, it was believed that the Earth was only a few thousand years old. It is difficult to believe now that people at the time of the Civil War had never seen nor even heard of a dinosaur, as the first fossils were not discovered until the 1890s. When early geologist James Hutton proposed that the earth was millions of years old, he was met with almost universal scorn and derision. In the short time that it has existed, historical geology has uncovered untold mysteries about the planet humans inhabit.