What if humans were actually sent to earth?
Humans evolved on Earth from earlier living things in an unbroken chain of life reaching back over a very long time. The Theory of Evolution and its predictive abilities is one of the most powerful tools ever uncovered by scientific method. If Humans were sent to Earth observations using the Theory of Evolution would likely spot it immediately.
The observations say... Humans are from Earth.
There are several well known science fiction stories that are based on this idea. And there are even some religions that claim this is how humans originated on earth. The mind of man can come up with all sorts of ideas like this. However the evidence that this actually happened is mighty slim.
Everything produce here only. There are thousands of species on earth. Do you ever saw anything fall from sky? Its not a big deal for, who created everything on earth so easily. Even mother don't aware at least 3-4 months.
Stop watching Star Trek and start reading books on evolution. I recommend Richard Dawkin's books The Blind Watchmaker and his later book Climbing Mount Improbable. Also, books by Stephen Jay Gould and his essays in older issues of Natural History Magazine. Ask your local library if they have these if you can't afford to buy books.