Radiometric dating of ordovician period
Sedimentary layers: The layers of sedimentary rock, or strata, can be seen as horizontal bands of differently colored or differently structured materials exposed in this cliff.
The deeper layers are older than the layers found at the top, which aids in determining the relative age of fossils found within the strata. Such index fossils must be distinctive, globally distributed, and occupy a short time range to be useful.
Misleading results can occur if the index fossils are incorrectly dated.
Stratigraphy and biostratigraphy can in general provide only relative dating (A was before B), which is often sufficient for studying evolution.
For example, if fossils of B date to X million years ago and the calculated “family tree” says A was an ancestor of B, then A must have evolved earlier.
It is also possible to estimate how long ago two living branches of a family tree diverged by assuming that DNA mutations accumulate at a constant rate.
If a fossil is found between two layers of rock whose ages are known, the fossil’s age is thought to be between those two known ages.
My thanks to both him and other critics for motivating me.There are several different methods for estimating the ages of fossils, including: Paleontologists rely on stratigraphy to date fossils.Stratigraphy is the science of understanding the strata, or layers, that form the sedimentary record.However, these “molecular clocks” are sometimes inaccurate and provide only approximate timing.For example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved, and estimates produced by different approaches to this method may vary as well.