To review our principles of relative dating as applied to such geologic cross-sections, we will make use of a neat learning tool available on the Internet.
"Athro Limited" is a private company which provides education modules on the Internet.
This chapter is an introduction to rocks and minerals, and the rock cycle.
Basic chemistry is important to all sciences, especially geology!
Prior to the late 17th century, geologic time was thought to be the same as historical time.
Archbishop James Ussher of Armagh, Ireland, 1654, added up generations from the Old Testament and determined that Earth formed on October 23, 4004 BCE.
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 order to do this, we need to apply the principles of relative dating which we have learned.The table below tracks the decay, half-life by half-life, of a radioactive isotope, and the accumulation of the daughter product isotope that the parent changes into once it decays. There are several different radioactive isotope systems that are used for measuring ages of geologic materials.For more information on these systems, see the isotopes and half-lives section of the Geologic Time Basics page.Cliffs, road cuts, and non-vegetated landscapes allow us glimpses into geology which is often hidden from view.Cliffs and road cuts are "side views" or "geologic cross-sections" of the topography which show the relative positions of various rock layers and structures at a given spot.