Answer:
The trilobite is the oldest.
Explanation:
In general terms (disregarding specific examples), the lower the level in the stratosphere, the older it is. In this case, the lowest level is taken by the trilobite.
Note however, that this is not always the case, especially near edges of the plates. Sometimes plates shift, which can cause certain older fossils to be moved upwards, while newer ones are shifted downward, as one plate "eats the other". Territory creations, including valleys and mountains when plates crash into each other, can also shift where a fossil is located.
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