It was popularly referred to as "the missing link" in human evolution.
Fluorine analysis is primarily used for verifying whether or not two fossils in the same strata at a site were in fact contemporaneous.
However, relative methods are , which is that if there are layers of deposits, those laid down first will be on the bottom and those laid down last will be on the top. However, geological strata are not always found to be in a neat chronological order.
Wind and water erode strata and some areas are uplifted or even tilted.
In other words, they may no longer be in their primary context.
When the bones of our early ancestors are found in the same geological strata as those of other animals that are known to have lived only during a specific time period in the past, we assume that these ancestors must also have come from that time.