Human or humankind is a race come to planet Earth after the appearance of Earth in the solar system. There are two types of human. They are the Nova-type human and the Earth-type human.
The Nova-type humans are cousins of the people who once inhabitant planet Earth. Dude to the effect of gravity, Nova-type human seems to be strong and fast as the Earth-type human. They have long adapted the environment of Nova Prime, this also makes them unable to breathe on Earth and have to use a special breath aids liquid in order to breathe and survive on Earth.
The Earth-type humans are humans that are born with a genetic defect that makes them less suitable for living on Nova Prime. They are named Earth Type Humans because during an experiment with Earth Type Human DNA, one scientist compared this DNA with preserved human DNA that dates back to the fall of Earth. Earth Type Humans are faster and stronger than the current Nova Prime Type Humans. Earth Type Humans require a special breathing fluid so that they don't suffocate in Nova Prime's atmosphere.