The Purple People Eater

A tiny invader lands and, as it grows to monumental proportions, It starts devouring the Earth and everything on it. A small group of people, who find themselves immune to Its attack, fight their way across an alien landscape right on the Earth, filled with hordes of the half-eaten, purple, zombie-like creatures that It turns people into as It eats them. As they band together with other immunes and the only non-immune and uninfected people left, they have to battle against the huge mind that It starts to acquire as It grows to cover the entire world. Their one chance at salvation; the ship orbiting up in space that was supposed to take a colony to Mars, but now might be mankind's last chance to survive and start again somewhere else.