Final answer:
Based on the provided conditions regarding the relative age of each artifact, the figurine is the oldest because there are no conditions stating that it is younger than any other artifacts.
Step-by-step explanation:
To determine which artifact is the oldest based on the provided conditions, we must first understand the sequence of their relative ages. According to the conditions, the headdress is older than both the plaque and the tureen. Additionally, the necklace is older than the tureen but younger than the figurine. This information helps us to infer the following order:
- Figurine is older than the Necklace
- Necklace is older than the Tureen
- Headdress is older than both Plaque and Tureen
This leads to the conclusion that the oldest artifact is the one that is not mentioned as being younger than any other, which, according to the conditions, is the figurine. Consequently, the figurine is the oldest artifact.