Geologists used fundamental concepts to understand the chronological order of rocks around the world.It wasn't until the advent of radiometric dating techniques in the middle 1900s that reliable dates could be assigned to the previously named geologic time divisions.Relative age dating also means paying attention to crosscutting relationships.

Age dating of rocks video

Unlike people, you can’t really guess the age of a rock from looking at it.

Yet, you’ve heard the news: Earth is 4.6 billion years old. That corn cob found in an ancient Native American fire pit is 1,000 years old. Geologic age dating—assigning an age to materials—is an entire discipline of its own.

Pretty obvious that the dike came after the rocks it cuts through, right?

With absolute age dating, you get a real age in actual years.

Geologic Time Scale Using a simple three or four generation family tree, students will construct a relatives time tree that mimics the major divisons of the geologic time scale (Precambrian, Paleozoic, Mesozoic, and Cenozoic). The time scale is divided into four large periods of time - the Precambrian, Paleozoic Era, Mesozoic Era, and Cenozoic Era.

National parks preserve fossils from each of these time blocks. The National Park System contains a magnificent record of geologic time because rocks from each period of the geologic time scale are preserved in park landscapes.Geologists use these concepts to place sequences of rock in chronological order: ) multimedia modules are part of the natural resource Science in Action series.Geologic Time Views Module The divisions of the geologic time scale are organized stratigraphically, with the oldest at the bottom and youngest at the top.The green bar indicates the ages of geologic units that are mapped within Great Basin National Park.To determine the relative age of different rocks, geologists start with the assumption that unless something has happened, in a sequence of sedimentary rock layers, the newer rock layers will be on top of older ones. This rule is common sense, but it serves as a powerful reference point.