this week's viewer question comes from chris humphreys. why does the earth have an atmosphere. and atmosphere is not all that unusual many bodies in our solar system have one like the giant planet jupiter in its moon europa. a planet develops an atmosphere when gases amerge from within it and when it collects volatile substances from collisions with asteroids and comets. though. the earth's atmosphere is a complex multilayered system up to an altitude of 90 kilometers it consists mostly of nitrogen along with the oxygen produced by living organisms. our atmosphere extends far into space reaching to the moon and even beyond. earth has enough mass to hold on to its atmosphere through gravity in contrast to mars. the red planet's gravity is. only $130.00 strong is ours causing it to lose of large part of its atmosphere it's as thin on the martian surface as the air is 30 kilometers above the earth's surface earth's atmosphere also has a magnetic field to protect it from the electrically charged particles of the solar wind mars lost its planetary magnetic field 4000000000 years ago