Risk: Cosmic rays are high energy particles fired at nearly the speed of light by the Sun, supermassive black holes and supernovae. They have the ability to blast right through your body, damaging DNA as they go. Long term exposure to cosmic rays increases your chances of getting cancer. Fortunately, we have our atmosphere to protect us. As cosmic rays crash into the atmosphere, they collide with the oxygen and nitrogen molecules in the air.
Risk: Gamma rays and X-rays. As you know, radiation can damage the body. Just a single high-energy photon of gamma rays can cause significant damage to a living cell. Once again, though, the Earth’s atmosphere is there to protect us. The molecules in the atmosphere absorb the high-energy photons preventing any from reaching us on the ground. In fact, X-ray and gamma ray observatories need to be built in space because there’s no way we can see them from the ground.
Risk: Ultraviolet radiation. The Sun is bathing the Earth in ultraviolet radiation; that’s why you get a sunburn. But the ozone layer is a special region of the atmosphere that absorbs much of this radiation. Without the ozone layer we would be much more exposed here on the surface of the Earth to UV rays, leading to eye damage and greater incidence of skin cancer.
Risk: Solar flares. Violent explosions on the surface of the Sun release a huge amount of energy as flares. In addition to a blast of radiation, it often sends out a burst of plasma traveling at nearly the speed of light. The Earth’s magnetosphere protects us here on Earth from the effects of the plasma, keeping it safely away from the surface of the planet. And our atmosphere keeps the X-ray/gamma ray radiation out.
Risk: Cold temperatures. Space itself is just a few degrees above absolute zero, but our atmosphere acts like a blanket, keeping warm temperatures in. Without the atmosphere, we’d freeze almost instantly.
Risk: Vacuum. Space is airless. Without the Earth, there’d be no air to breath, and the lack of pressure damages cells and lets water evaporate out into space. Vacuum would be very, very bad.
If you’d like to hear more about cosmic rays, listen to this episode of Astronomy Cast.