Why do the gases in the atmosphere not float off into space?

The gases in the atmosphere do not float off into space due to the Earth's gravitational pull, which keeps them bound to the planet. Additionally, the atmosphere is held in place by the balance of forces, including the kinetic energy of gas molecules that causes them to collide and create pressure. This pressure helps maintain the density of the atmosphere, preventing the gases from escaping into space. Finally, the thermal structure of the atmosphere, including temperature gradients, also influences the behavior of these gases, contributing to their retention.