The Elemental Stone was a very large gem that inhabited almost all of the Planet Chronus. It slowly consumed the planet day by day, and most of the inhabitants had left. Those who haven't left yet or refuse to leave were likely to be absorbed by it. Only those who have strong spirit can even be near a power of that magnitude, let alone control it.
The stone itself was supposedly harder than diamond, or even Katchin (DBZ, Had to use something). However, this was disproved when a huge comet struck the stone, and shattered it, saving the remaining inhabitants. Most of the stone was destroyed upon impact, but small fragments were scattered across the universe, one of which landed on Earth. It was first discovered 5000 years ago. Technology flourished, magitechnology was invented and rapidly advanced. But all good things must come to an end.
That's where the dragons came from. They somehow learned of Earth's advancement, and began to observe the planet to find out why. They soon learned that a fragment of TES had landed on the planet and was being used as a power source. A huge garrison of soldiers floods Earths sky and fireball rain down upon the land. The 3 most powerful warriors, The Elemental Swordsman, Sorceress, and Sorcerer combined their powers and fended the dragons off.
Earth was left a barren wasteland. Realizing that this would scar the planet and its inhabitants for eternity (or whenever the planet decides to blow up), The three used their remaining power to revive the land, and erase everyone memory of what happened. They then split the stone into seven shards, and scattered them across the planet. In doing so they drained their remaining lifeforce and faded away.