Dating Methods in Paleoanthropology Dating in Context 1820 For constructing evolutionary sequences and correlating event across continents and the globe Historical geologists looked for evidence of the biblical flood Charles Lyell o Found a lot of fossils o Couldn t all be from on event flood o Uniformitarianism All geologic phenomena are the result of existing forces having operated uniformly from the origin of the earth to the present Implied great antiquity of Earth Overcame a great impediment to scientific though the age of the earth Long term Evolution Earth is 4 5 billion years old Absolute dating Specific age in year BP before present Examples of absolute dating o Carbon Dating 200 50 000 years ago 14C radioactive isotope decays into non radioactive isotopes 12C and 13C 14C has a half life of 5 730 40 years proportion 12C to 14C increases with time o Potassium argon dating Used on volcanic tuff in eastern Africa 40K 40Ar or 40Ar 39Ar Half life of 1 3 billion years o Uranium series dating Used on tufa speleothems and apatite 238U or 235U daughter isotopes Half life of 4 47 years Problem with diagenesis mineral replacement Old rock is being replaced with newer rock limestone o Paleomagnetism Shifts in earth s magnetic poles Reversal North becomes South South becomes North Take place at slightly irregular intervals o Electron Spin Resonance Detects presence of unstable electrons trapped in solids years Useful for sites around 100 000 to 2000 000 Larger margin of error at older sites Relative Dating Examples of Relative Dating o Superposition Older things are on the bottom and newer things are closer to the top Formations Members and Beds Members Beds Units of formations Units of members o Faunal Dating Guild fossils and faunal seriations Faunal seriations Compare similarities amount presence of species in faunal assemblages FADs and LADs vs Origins and Extinctions FAD LAD First appearance dates Last appearance dates