We'll even visit the Grand Canyon to solve the mystery of the Great Unconformity!

Imagine that you're a geologist, studying the amazing rock formations of the Grand Canyon.

With out individual time stamps the process of dating these structures could become extremely difficult.

To deal with many of these problems geologists utilize two types of geologic time: relative time and absolute time.

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 dating' as observed in geology from the 17th century to the early 20th century.

The regular order of occurrence of fossils in rock layers was discovered around 1800 by William Smith.

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.

For a fossil to be a good index fossil, it needs to have lived during one specific time period, be easy to identify and have been abundant and found in many places. If you find ammonites in a rock in the South Island and also in a rock in the North Island, you can say that both rocks are Mesozoic.

Free 5-day trial Discover how geologists study the layers in sedimentary rock to establish relative age.

Learn how inclusions and unconformities can tell us stories about the geologic past.

Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence.

The method of reading the order is called stratigraphy (layers of rock are called strata).