Final answer:
The Jinniushan skeleton was dated using stratigraphic analysis and fluorine dating to approximately 260,000 years ago. Details on Lu's argument regarding layer 7 are not provided. Other fossils and remnants of early human life have been found at the site.
Step-by-step explanation:
The Jinniushan skeleton was dated using a combination of stratigraphic analysis and fluorine dating techniques, which are common methods in paleoanthropology for determining the age of archeological finds. As for the age, the skeleton was estimated to date back to approximately 260,000 years ago. Concerning the argument by Lu about layer 7, it is suggested that further details are needed specific to Lu's research to understand what was being argued exactly. However, typically, layer-based arguments would pertain to the stratigraphy and the context of findings which helps in the interpretation of the site's history and the artifacts' chronology. At the Jinniushan site, which is known for its significance in understanding human evolution, various other fossils and remnants of early human life have been discovered along with the skeleton.