Get off my lawn.

Being born after 2000 should be illegal

I have... and by way longer than I want to admit.

If you like pedantry, people have definitely flown in vehicles and even jumped.

We are all passengers on a generational space vessel.

It's the year 3250. Two harsh desert planets are in a bitter dispute over mineral and water mining rights over the asteroid belt. The Mars coalition insists that Earth may lay claim only to those rocky bodies that fall past her orbit. Earth insists that anything beyond their respective atmospheres is fair game. They use loaded language and plan to argue that an 'atmosphere' is one that sustains life, meaning she plans to mine uninhabited stretches or Martian soil too. There is serious debate on Earth of the inhabitants of Mars are even human anymore, cross breeding has become exceptionally difficult. Martians have a lower natural fertility rate and often need IVF to reproduce. Earth gravity is too strong for martians to safely return to the home planet, and so few Earthlings have ever seen one in person.

The dispute, unresolved, leads to the second interplanetary war. A billion people will die on both planets. Mars will lose precious irreplaceable atmosphere. Earth will lose access to much needed water. The conflict only ends when neither can keep up the fight any longer.

that would be the first time not all of humanity was on earth

China will still have an operational station. Probably.

Well, maybe sooner than 2030... https://spacenews.com/musk-calls-for-deorbiting-iss-as-soon-as-possible/

I mean 30,000 feet is 9km. The Kármán line is 100km. The ISS is at an average altitude of 400km.

It's a bit like saying people in planes don't count as flying because then people on trampolines should count.

We already have a definition for this, the Karman line.

Unless you define "on earth" to be "below the Kármán line. The Earth's atmosphere is probably to be considered part of the planet, else gas planet like Jupiter get difficult to talk about consistently. Atmospheres don't have a proper "cutoff", they just get thinner and thinner until they gradually become insignificant, so some cutoff is going to have to be arbitrarily defined to make the distinction useful.

Spent a moment thinking about this and I think there's an implied definition for what "on earth" means that we intuitively accept but don't ever really need to state.

If your projected free-fall trajectory both forward and backward in time intersects with the surface of the earth then you are "on earth".

Standing on the ground? Intersects twice. Thrown rock? Intersects twice. Person in an airplane? Intersects twice. ISS? No intersection. Incoming impact meteor? One intersection.

Let's make some artificial rule like you need to be not on earth for 48 hours to be not on earth or something ...

Long term occupancy of the ISS started in November 2nd, 2000. Since then there has always been at least one person Manning the ISS.

So at least one human has not been on earth for every day since then, thus, all of humanity was last on earth on November 1st 2000. The statement is factually correct.