When museums and collectors purchase archaeological items for their collections they enter an expensive and potentially deceptive commercial fine arts arena.
Healthy profits are to be made from illicitly plundered ancient sites or selling skillfully made forgeries.
Tree ring dating offers over 1,000 years of clues in dates of artifacts from the American Southwest.
Radiocarbon dating provides additional clues necessary for absolute dating.
Artifacts from the earliest dates are in the lower levels or strata of Earth.
Since certain species of animals existed on Earth at specific times in history, the fossils or remains of such animals embedded within those successive layers of rock also help scientists determine the age of the layers.
Similarly, pollen grains released by seed-bearing plants became fossilized in rock layers.
When you talk about the Precambrian, Paleozoic, Mesozoic, and Cenozoic on Earth, or the Noachian, Hesperian, and Amazonian for Mars, these are all relative ages.
Relative-age time periods are what make up the Geologic Time Scale.