Relative age dating vs absolute age dating
With a rock record that spans more than 1500 m.y., Grand Canyon is truly a panoramic view into the geologic past.
Nonetheless, how geologists determine the age of rocks is a mystery to many members of the public, and even to many park rangers [see Photo 2], guides, and others who share the canyon’s geologic story with others. ” when geologists say a Grand Canyon rock formed 270 million years ago.
Geologists generally know the age of a rock by determining the age of the group of rocks, or formation, that it is found in.
The age of formations is marked on a geologic calendar known as the geologic time scale.
Absolute dating places events or rocks at a specific time.
If a geologist claims to be younger than his or her co-worker, that is a relative age.
Prior to the late 17th century, geologic time was thought to be the same as historical time.Before this, archaeologists and scientists relied on deductive dating methods, such as comparing rock strata formations in different regions.Chronometric dating has advanced since the 1970s, allowing far more accurate dating of specimens.There are younger geologic deposits in Grand Canyon too, such as the Ice Age fossils found in caves, a 1000-year-old lava flow in the western canyon, and even the debris flow deposits that continue form each year.Yet, it is the canyon’s rock walls that allow people to develop their greatest perspective on geologic time, because of these rocks’ immense age, their fossil record, and because these rocks formed in environments far different than those found in northern Arizona today.