Functional interpretation of the Laetoli footprints. CT-scans shows small canine teeth forming in the skull, telling us this individual was female.
Sedimentary rock is made of particles derived from other rocks, so measuring isotopes would date the original rock material, not the sediments they have ended up in.
However, there are radiometric dating methods that can be used on sedimentary rock, including luminescence dating.
For example, the decay of potassium-40 to argon-40 is used to date rocks older than 20,000 years, and the decay of uranium-238 to lead-206 is used for rocks older than 1 million years.
Radiocarbon dating measures radioactive isotopes in once-living organic material instead of rock, using the decay of carbon-14 to nitrogen-14.
The atoms of some chemical elements have different forms, called isotopes.
These break down over time in a process scientists call radioactive decay.
Because of the fairly fast decay rate of carbon-14, it can only be used on material up to about 60,000 years old.
Geologists use radiocarbon to date such materials as wood and pollen trapped in sediment, which indicates the date of the sediment itself.
This child's baby teeth had erupted in a pattern similar to a three-year-old chimpanzee’s, telling us she grew up at a rate similar to a chimpanzee.
(Eds) From Biped to Strider: The Emergence of Modern Human Walking, Running, and Resource Transport. studies indicate they ate soft, sugar-rich fruits, but their tooth size and shape suggest that they could have also eaten hard, brittle foods too – probably as ‘fallback’ foods during seasons when fruits were not available.
This is different to relative dating, which only puts geological events in time Most absolute dates for rocks are obtained with radiometric methods.