It depends upon the definition of “on”, I suppose.
If jumping or falling count as not being “on” earth, the fact is not true since there is (a) almost no chance with so many people that one person (probably a child) somewhere wasn’t jumping or falling and (b) we can’t definitively prove things one way or the other with regard to (a).
If we do say “OK, human-body-powered times not in contact with earth don’t count” (assuming the human is responsible here for cases where they fall, for simplicity), we would have to move on to vehicles. Driving a vehicle that contacts the ground seems pretty “on earth”. I suppose boats would as well. What about planes, thought? They’re definitely “in the air” when they’re not “on the ground” (I’m sticking with English here since the post is in English; we could open another can of words worms for other languages).
So next we have to say “things flying in the atmosphere don’t count” then we have to either define atmosphere or define an arbitrary line of Xkm above the average surface of earth. In the case of the former, how much atmosphere counts as atmosphere?
I guess we could move on to gravity well after that.
define atmosphere or define an arbitrary line of Xkm above the average surface of earth.
100km. Atmosphere is a gradient so yes it’s entirely arbitrary.
If a person fell into the singularity of a black hole that had particles from our atmosphere, are we back to on earth again? (My vote is “s/he dead and no even if not”, but I think it’s interesting to think about).
It’s pretty easy to draw a line at orbit at any altitude. If you are staying aloft by moving fast enough that a straight line in the planet’s gravity well forms a closed ellipse, or faster, that excludes jumping (and every other sorry of suborbital movement), flying, floating (on water or in air; nothing we have made our can imagine can float on air)
Orbit is different to everything not orbital in a more significant way than other modes are different to each other
I think you can even word your way around how flying is on Earth, in that you’re supported by the gaseous part of Earth, just like a boat is supported by the wet part of Earth
You cannot get out of Earth’s gravity. Gravity stretches out to the edge of the observable universe though it gets pretty weak outside the solar system
