A Conversion mission has a 200 points score. This means whenever a ship lands and takes off again, you lose 200 points. There's four ships doing two landings each (4x2x200), so that's 1600.
An Alien Base mission also has a score of 200 and 8 landings as well; 7 if there is no base yet. So that's 1400.
Sway Government has a 300 points score and 6 landings, so that's 1800.
Pacification only has a 100 points score and 8 landings, so that's 800 points.
Please note that the above are in addition to the points generated by UFOs flying on the map (1 per 30 minutes) or landed (2 per 30 minutes). So yes, a 3600 score can happen in 13 days if two high-scoring missions are triggered at the same time.