[Flat is Earth]

How do we know that antarctica exists?

[existoid]

How do we know that antarctica exists?

Here are some of the ways "we" could know that Antarctica exists (I assume by "we" you mean human knowledge writ large).

1. Humans can travel close to or on to it and document their visit with writings, photos, and videos. Some human organizations do this regularly, usually for scientific, economic or leisure purposes. (Examples of photos from leisure trips here: https://expertvagabond.com/antarctica-pictures/ )

1a. Corollary: we can infer its existence from scientific writings by humans who went there not to document its existence, but other phenomena (e.g., life cycles of penguins; geology; marine life in the littoral zone, etc.). Stuff that is reported here, for example: https://www.scar.org/

2. Satellites can take images of it from orbit. (example: https://www.nytimes.com/2018/09/07/science/antarctica-map-rema.html )

3. Planes can fly over it and document it.  (Third picture in this article claims to be of Antarctica from a Qantas jet: https://www.traveller.com.au/why-dont-airlines-fly-commercial-routes-over-antarctica-plan-for-perthbuenos-aires-nonstop-h1dq5r )

4. We can unearth and unfreeze an alien intent on absorbing all life on earth and then destroy it in fire to keep the rest of the world safe. This was documented in 1981.