Relative dating laws and principles
This also means that fossils found in the lowest levels in a sequence of layered rocks represent the oldest record of life there.
By matching partial sequences, the truly oldest layers with fossils can be worked out.
Once students begin to grasp "relative" dating, they can extend their knowledge of geologic time by exploring radiometric dating and developing a timeline of Earth's history.
These major concepts are part of the Denver Earth Science Project's "Paleontology and Dinosaurs" module written for students in grades 7-10.
Specific rock formations are indicative of a particular type of environment existing when the rock was being formed.
For example, most limestones represent marine environments, whereas, sandstones with ripple marks might indicate a shoreline habitat or a riverbed.
In reading earth history, these layers would be "read" from bottom to top or oldest to most recent.
If certain fossils are typically found only in a particular rock unit and are found in many places worldwide, they may be useful as index or guide fossils in determining the age of undated strata.However, "relative" dating or time can be an easy concept for students to learn.In this activity, students begin a sequencing activity with familiar items letters written on cards.Scientific measurements such as radiometric dating use the natural radioactivity of certain elements found in rocks to help determine their age.Scientists also use direct evidence from observations of the rock layers themselves to help determine the relative age of rock layers.Return to top The study and comparison of exposed rock layers or strata in various parts of the earth led scientists in the early 19th century to propose that the rock layers could be correlated from place to place.