In rock layers, jellyfish fossils are found lower than trilobite fossils, and trilobite fossils are found lower than ammonite fossils. What can be determined from this information?

In undisturbed rock layers, lower layers are generally older than the layers above them. Since jellyfish fossils are below trilobite fossils, and trilobite fossils are below ammonite fossils, jellyfish existed first, followed by trilobites and then ammonites. Therefore, the correct choice is “Jellyfish existed before trilobites and ammonites.”

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