An archaeologist finds evidence of early human activity in a cave. This evidence includes volcanic rocks that were used for tools and charred seeds from a fire pit. The archaeologist uses carbon-14 dating on the seeds and uranium-235 dating on the rock tools. The seeds contain no carbon-14 but large amounts of nitrogen-14. The rock tools contain large amounts of uranium-235 and only tiny amounts of lead-207. When were early humans most likely living in the cave and using the seeds and tools?