Even rocks age
All rocks were not created equal, or even at the same time. Rock is constantly being created by lava flow and pressure, just as rocks are being destroyed by erosion. Knowing the age of rocks is absolutely essential in order to understand the history of the planet we inhabit. By dating rocks, we are able to date fossils and get an approximate dates for ancient plants and animals.
Geologic Time
The earliest method of dating rocks is also the simplest. According to the U.S. Geological Survey, the Principle of Superposition says that new layers of rock are created on top of old rocks. Erosion deposits new material. Plants and animals die and decompose, leaving their minerals in the soil. This means that the deeper the rock, the older it is. But the problem with this method is that it only tells the relative age within a rock structure, not how old the entire formation would be. In order to give a more specific date, other methods of dating must be used.
Radiometric Dating
Radioactive isotopes decay at a standard rate. Many of these elements decay too quickly to be of any use. But some have much longer half lives. According to the Smithsonian Institute, Uranium 235, for example, decays over 704 million years to become Lead 207. Samarium 147 takes 106 billion years to decay into Neodymium 143. When attempting to date a rock, the geologist looks for any of these trace minerals. They compare the rate of the parent isotope to the daughter and use the ratio to date the creation of the rock. Unfortunately, when it come to sedentary or aggregate rocks, this only tells the age of when the composite stone was created. It doesn't tell when all the parts came together to become the new stone.
Paleomagnetics
According to NASA, the North Pole is currently shifting about one degree per decade. Over the last millions of years, the North Pole has swapped places with the South Pole several times. When the iron is present in liquid magma, the metal lines up with the magnetic field of the earth at that time. They freeze in place when the liquid rock cools, giving geologists a picture of the magnetic fields. By comparing these fields, paleogeologists can date the rock.
Tags: date rock, dating rocks, North Pole, only tells
