Arthropods invaded land about 100 million years before vertebrates did so. This most clearly implies that

Co-evolution

Explanation:

The given statement implies that arthropods had more time to co-evolve with land plants than vertebrates

Co-evolution is a type of evolution in which two species reciprocally affect each others evolution in a way that they both evolve togetherFossil evidence gives the progressive interaction between arthropods and land plants through the later Paleozoic and Mesozoic eraEvidence includes the evolution of chemical defense strategy by plants along with the evolution of different mouthpart design in new insect groupsLeaf galls became common in  Cretaceous coinciding with the evolution of several new insect groups and plantsData from coprolites(trace fossils) suggest that spore feeding preceded leaf feeding,experiments have indicated that some spores remain viable after passing through the gut and hence this feeding habit might have been advantageous to some early plants for propagule formation

Genetic engineering is the answer.

The type of rock she find is a sediment rock