The most recent change of all is the modern bridge support.We know it is the most recent because it has cut through all of the others.The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah is a great example of Original Horizontality and the Law of Superposition, two important ideas used in relative dating.These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park.Geologi Sts refer to surfaces between layers or other bodies of rock as contacts. the contact between the red ancient soil and the lava flow. :hc exact contact bcrween the top ofthe lava ﬂow and the base ofthe , \ ‘ _ ' ..
Look at the two nearly identical diagrams, Figures 7 and 8.Here is an easy-to understand analogy for your students: relative age dating is like saying that your grandfather is older than you.Absolute age dating is like saying you are 15 years old and your grandfather is 77 years old.Then place arrows along the right edge of the mke that point to each contact. Label each arrow (contact) to show its relative age from 1 (the time when the ﬁrst contact was created: the oldest contact) to “n" (the number corresponding to the last time a contact was created; the youngest contact). The picture below is an outcrop about 5 meters thick near Sedona, Arizona. The brown layer in which grass is rooted is modern soil. From the beginning of this course, we have stated that the Earth is about 4.6 billion years old.How do we know this and how do we know the ages of other events in Earth history?The order of events in the archaeological cross section shows that the oldest remains are Roman.After this the medieval remains are more recent and the industrial remains are more recent still.The blocky brown-gray rock with wide fractures (cracks) is an ancient lava flow (basalt. This outcrop is a natural geologic cross section of rock layers. A fill/n S‘Vl/ 217 ACTIVITY 8.1: Geologic Inquiry for Relative Age Dating 8.1A. Principles of Stratigraphy Stratigraphy is the study of strata (sedimentary layers) in the Earth's crust.Geologist in the 1800s worked out 7 basic principles of stratigraphy that allowed them, and now us, to work out the relative ages of rocks.In a way this field, called geochronology, is some of the purest detective work earth scientists do.