Four-thousand years ago, before The Big Wave, the Knuckles Clan attempted to raid the Chaos Emeralds from Chaos, the protector of the Chao. Chief Pachacamac attacked Chaos, despite his daughter Tikal's warnings.
The clan was quickly overwhelmed by the guardian's wrath, ravaging the land they lived on, fire surrounding every corner of it. To stop Chaos from causing anymore havoc, Tikal sealed herself and Chaos in the Master Emerald.
...But something went wrong.
Instead of sealing the guardian and keeping him from causing more havoc, he tried to drain the Master Emerald of its energy and merge it within himself. With no other options, Tikal shattered the Master Emerald, leaving her and Chaos partially free, but unleashing the weakened version of Chaos' power out, causing what is known as The Big Wave. A cataclysmic flood that spread to several corners of the world and possibly others, effectively erasing Angel Island's history, and the Chaos Emeralds.
Now in the present day, Sonic may have incidentally uncovered a hidden part of history, all by making a bet.
(Sonic the Hedgehog and their official characters are owned by SEGA.)