How does geology figure in the study of hominids? Primarily in learning how old the fossils are and what the environment was like that that they lived in.
Q: Bill Nye once said, that if you ever have an example of a fossil ever being discovered in a layer of earth that is from a different era that it would change the way we think about evolution and would be monumental. Now I find the evidence that science produces is the most compelling of any other narrative that we have of the world past, present and future. However, to maintain the credibility and ethical integrity of logic and reason. You must question and if it doesn't fit you must discard the idea. So, the question is. How is it that in 1959 and 1960, the fossils of Zinjanthropus and Homo Habilis both dated at 1.8 million years be found in the same geological layer? The layer that Mary Leakey was walking on when she accidentally stumbled upon the missing link. Both were found away from dig sites so the earth wasn't excavated. Mr. Leakey was ill when he first laid his eyes on Zinj. Suppose he dropped dead right then and his body was never moved. Future diggers would find two 1.8 million year old skull fragments and that of Leakey's all in the same geological layer.
– Levi T
A: First, the fossil record for hominids is incredibly sparse. The precision of most age-dating technologies is also not as precise as numbers on a popular science graph might suggest. It is thus really stretching it to draw any age conclusions unless you have U/Pb or other dates directly from the bones. It is extremely rare, however, that you will find adequate (undisturbed) isotopic content to do reliable dating with fossilized hominid remains; this leaves you with dating the stratum they are found in. In east Africa there are a lot of volcanic ash deposits that are relatively easily dated. Thus, for instance, you can say that a fossil tooth was found between ash layer X and ash layer Y, which are both dated - so you can place the hominid between these two ages.
Second, it is now known that different hominids (for example, Homo Erectus, Homo Habilis, and Homo Paranthropus) overlapped in time - they were on the same continent and perhaps even in direct physical contact during their range of existence.
Third, the nature of decomposition and fossilization are such that Louis Leakey would leave remains dramatically different than something 1.8 million years old.
Fourth, there is also a big difference between a conformable and an unconformable geologic contact. It's pretty obvious if something was buried at the time the sediments were forming vs afterwards.