Answer:
Paleozoic
Step-by-step explanation:
The first insect fossils are dated to the Devonian, but because of the development of the genetics, the scientists have been able to trace the appearance of the first insects in the Ordovician. The insects originated from the crustaceans. Initially they were walking on land, but they hadn't developed wings. The wings came to develop in some insects in the Devonian, and since than it has gradually became one of their trademark features. It is interesting that the first insects actually appeared at the same time with the first terrestrial plants, and also that they are the first organisms to develop wings and be able to fly.