The Karman line is regarded by most people to be the beginning of space, most of the Earth's atmosphere is below that imaginary line but there is still a thin atmosphere above which gets thinner the farther up you go.
How far up from the surface of the Earth is the Karman line?
100 kilometres / 300 kilometres / 600 kilometres
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Answer to question 4 / 100 kilometres.
Yes, our atmosphere is very thin compared to the size of our planet. The space station orbits the Earth at 420 kilometres from its surface, commercial aeroplanes can fly at over 10 kilometres high.