Correlating radioisotope dating methods new dating sties
Biologists actually have at their disposal several independent ways of looking at the history of life - not only from the order of fossils in the rocks, but also through phylogenetic trees. Relative dating is done by observing fossils, as described above, and recording which fossil is younger, which is older.The discovery of means for absolute dating in the early 1900s was a huge advance.Early geologists, in the 1700s and 1800s, noticed how fossils seemed to occur in sequences: certain assemblages of fossils were always found below other assemblages. Since 1859, paleontologists, or fossil experts, have searched the world for fossils.In the past 150 years they have not found any fossils that Darwin would not have expected.Older dates may change by a few million years up and down, but younger dates are stable.
This hands-on activity is a simulation of some of the radiometric dating techniques used by scientists to determine the age of a mineral or fossil.The activity uses the basic principle of radioactive half-life, and is a good follow-up lesson after the students have learned about half-life properties.See the background information on Students will use half-life properties of isotopes to determine the age of different "rocks" and "fossils" made out of bags of beads.Results from different techniques, often measured in rival labs, continually confirm each other.Every few years, new geologic time scales are published, providing the latest dates for major time lines.