Great Question! This is a really interesting topic, and pretty cool too!! Black holes don’t actually form in the Earth’s atmosphere itself. The atmosphere is a mixture of nitrogen (78%), oxygen (21%), and other gases (1%) that surrounds Earth.
A black hole is formed in space where gravity pulls so much that even light cannot get out. The gravity in a black hole is so strong because matter has been squeezed into a tiny space. One of the things which could cause this is when a star is dying. Black holes can only be seen using space telescopes with special tools. The special tools can see how stars that are very close to black holes act differently than other stars.
The theory is that the smallest black holes formed when the universe began. Also, when the centre of a very big star falls in upon itself, or collapses stellar black holes are made. This process is called a supernova. A supernova is an exploding star that blasts part of the star into space.
Scientists think supermassive black holes were made naturally at the same time as the galaxy they are in.
Yes it’s possible. Micro-black holes are allowed under the laws of quantum mechanics and may exist in very high energy environments such as inside a particle accelerator. If you remember when the Large Hadron Collider was first turned on, some people were worried that it might cause the end of the world by the Earth being swallowed up by a black hole. The experts, including Steven Hawking who has looked at this problem, say that any micro black hole formed would instantly evaporate.
Artificial black holes have also been proposed as a means of generating energy to be used on Earth!