5 relative dating principles
Many of the largest mountain ranges and broadest zones of seismic activity come from collisions..
Comparisons of carbon ages with tree-ring data and other data for known events have allowed reliable calibration of the radiocarbon dating method.
Using this time scale, geologists can place all events of Earth history in order without ever knowing their numerical ages.
The specific events within Earth history are discussed in Chapter 8.
The principles of relative time are simple, even obvious now, but were not generally accepted by scholars until the scientific revolution of the 17th and 18th centuries via Wikimedia Commons' src=" Superposition-228x300.jpg" alt="Photo of superposed strata with the younger on top of the older" width="270" height="355" srcset=" Superposition-228x300228w, Superposition-768x1009768w, Superposition-780x1024780w, Superposition-1200x15761200w, 1392w" sizes="(max-width: 270px) 85vw, 270px"/CC BY 2.0], via Wikimedia Commons' src=" alt="Photo of rock outcrop with a dike cutting through an older rock and another dike cutting across that one." width="215" height="287" srcset=" sizes="(max-width: 215px) 85vw, 215px"/ Wikimedia Commons, via Wikimedia Commons' src=" alt="Photo of the Grand Canyon showing expanse of canyon and the various rock layers" width="392" height="261" srcset=" sizes="(max-width: 392px) 85vw, 392px"/CC BY-SA 3.0], via Wikimedia Commons' src=" alt="The red rocks are layered, the dark rocks are not." width="300" height="225" srcset=" sizes="(max-width: 300px) 85vw, 300px"/All three of these formations have a disconformity at the two contacts between them.
An atom that has different number of neutrons but the same number of protons.
Relatively chemically inert with a hardness of 8.5.
Common accessory mineral in igneous and metamorphic rocks, as well as detrital sediments.
Uranium can substitute for zirconium, making zircon a valuable mineral in radiometric dating.
Many geological samples contain multiple parent/daughter pairs, so cross-checking the clocks confirms that radioisotopic dating is highly reliable.