The birth of the solar system created Earth’s earliest atmosphere. Huge quantities of materials orbiting the Sun fused together into proto-planets. Jupiter and Saturn formed into gassy spheres. But on Earth, most of the material condensed into a molten core. The remaining gases bubbled forth from the liquid rock, forming the first atmosphere. 

 

Our planet’s gravity stopped these gases from drifting off into space. But Earth now had to face the ravages of the solar wind, a stream of charged particles thrown out by the Sun. This same wind had a catastrophic effect on Mars. It has stripped the air from the planet’s surface, blasting it deep into space. The Red Planet’s atmosphere is now only a hundredth as thick as Earth’s.