Relative age dating of sedimentary rocks
But this sediment doesn't typically include the necessary isotopes in measurable amounts.Fossils can't form in the igneous rock that usually does contain the isotopes.In addition, the oldest known moon rocks are 4.5 billion years old.Since the moon and the Earth probably formed at the same time, this supports the current idea of the Earth's age.Prior to the discovery of radiometric dating in the early 20th century, which provided a means of absolute dating, archaeologists and geologists used relative dating to determine ages of materials.Though relative dating can only determine the sequential order in which a series of events occurred, not when they occurred, it remains a useful technique.Photo from Glen Canyon National Recreation Area, Utah.Relative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age (i.e. In geology, rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another.
The Law of Superposition, which states that older layers will be deeper in a site than more recent layers, was the summary outcome of 'relative datin g' as observed in geology from the 17th century to the early 20th century.Some of the isotopes used for this purpose are uranium-238, uranium-235 and potassium-40, each of which has a half-life of more than a million years.Unfortunately, these elements don't exist in dinosaur fossils themselves.These layers are like bookends -- they give a beginning and an end to the period of time when the sedimentary rock formed.
By using radiometric dating to determine the age of igneous brackets, researchers can accurately determine the age of the sedimentary layers between them.You can learn more about fossils, dinosaurs, radiometric dating and related topics by reading through the links below.