Well I think there were Giants on earth. They didn't come from earth though. No, they came from a planet called Giantanus, which used to orbit between Uranus & Neptune until cosmic forces thrust it out of the solar system. The gravitational pull reacted to the planets shift which allowed for the skeleton to grow and support the larger framework.
People think that giants are dumb, but that's dumb. The bigger the body got, the larger the brain got. These were highly intelligent beings. Thousands of years later they developed spacecraft that allowed them to travel from galaxy to galaxy. One year, during spring break, some of the college student giants thought it would be cool to visit what we now call Cancun Mexico. They gathered up some of their pets and flew to earth for vacation. Unfortunately, they were not used to being so close to a sun, and they used SPF 5 Suntan Lotion rather than the SPF 30 they should have been using. They all died from horrible sunburns. There pets were left to roam the land...we call them dinosaurs.
So I just cleared up 2 mysteries in one.