Obsidian tools like arrowheads can be dated extremely accurately. When you chip obsidian that fresh obsidian begins to develop a rind of sorts as it’s exposed to water in the atmosphere. Much like carbon dating this happens at a very predictable rate. This in conjunction with superposition adds more accuracy. I’m not an expert I just took one class in college. I’m sure someone more educated can go into specifics.
There’s no way to directly measure when a rock was shaped into a tool, but we can indirectly measure it a few ways. One would be to date the sedimentary layers the tool is found in. Another way would be to directly date the remains of organic materials found in the same layer of rock as the tool, or near the tool. For example, if we found a stone arrowhead next to the bones of an animal in the same layer of rock, we can date the bones directly and that will tell us the age of the tool.
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