Genesect is 300 Million years old, but Team Plasma altered it and attached a cannon. The purple Genesect was probably a clone or something. I would say it was revived from a fossil, because it is 300 Million years old. I don't think a pokemon can live that long. So like I said, the purple one could be a clone.
This was taken from Bulbapedia:
Genesect was revived from a Fossil and technologically enhanced by Team Plasma to create the most powerful Pokémon ever. N had the project cancelled and the P2 Laboratory closed because he felt that Pokémon, who he thought to be perfect beings, would lose their beauty if modified by science. However, Scientist Dudley kept working on it, angry that N denied his talent. This scientist reconstructed Genesect and installed the cannon on its back.