© NASA/ESA/Hubble Heritage TeamThe Veil Nebula Supernova Remnant.
The most dangerous parts of a supernova explosion are the outputs like X-rays and gamma rays. Even though they only share a small fraction of a
supernova's power, they are
extremely dangerous. But they're not going to disintegrate the Earth. We are simply too far away from any potential supernova for that to ever be a problem.
What can happen is that these forms of radiation pack enough energetic punch that they can
tear apart molecules. Elements like nitrogen and oxygen prefer to float around as molecules in our atmosphere. But then once they get hit by x rays, gamma rays, and cosmic rays, they get broken apart. And then they recombine in interesting and fascinating ways like various nitrogen oxides, including everybody's favorite nitrous oxide AKA laughing gas. And while everyone's laughing and having a good time, our ozone layer gets stripped away.
That's the danger of a too-close supernova: it breaks up our ozone layer. And without an ozone layer, it means the Earth is vulnerable to ultraviolet radiation from the Sun. Our ozone layer protects us from the vast majority of ultraviolet radiation. There are a couple specific bands of wavelengths that do sneak through, which is why we need to wear sunscreen here on the surface, so we don't get nasty tans and sunburns and skin cancer and all that.
But imagine no ozone layer, then you get all the UV radiation, the full output, and it's bad. And it's not just a matter of quicker tans and faster burns and higher rates of skin cancer. The problem is that photosynthetic microorganisms like algae become vulnerable. They get cooked and then they die. And since they form the very base layer of the food chain, you end up with whole ecosystem collapse and a mass extinction.
