On 25Jan2020 0941, Bruce Johnson wrote:
> https://scied.ucar.edu/shortcontent/earths-atmosphere  > > "Air becomes so thin at altitudes between 100 and 120 km (62-75 >
miles) up that for many purposes that range of heights can be >
considered the boundary between the atmosphere and space. However, >
there are very thin but measurable traces of atmospheric gases >
hundreds of kilometers/miles above Earth's surface.” > > 1000km is MUCH
higher than needed to contain atmosphere. you MIGHT > actually be able
to see the top of the wall with a telescope long > before you could see
the bottom.
I always assumed that the extra height was to slow loss to solar wind
and general diffusion over cosmic timeframes.

--
Rupert Boleyn <xxxxxx@gmail.com>