It might be because i skipped to much class, but i think i remmeber having my teacher doing some math that earth isn't big enough, aswell as human mankind isnt inteligent yet to create a black hole that would devour us all.
Ah well, i would like getting spagettio'ed.
You're teacher is incorrect. All it takes, is for an object to become dense enough that the gravity itself can capture light. Those objects can be as large as our solar system (super massive black holes found in the center of galaxies) or microscopic black holes on the planck (quantum) scale.
"To make a black hole, one must concentrate mass or energy sufficiently that the escape velocity from the region in which it is concentrated exceeds the speed of light. This condition gives the Schwarzschild radius, R = 2GM / c2"
http://en.wikipedia.org/wiki/Micro_black_hole#Minimum_mass_of_a_black_holeBasically, collide 2 particles at high enough energy, you get a black hole. Though, in theory, you need hundreds of TeV of energy to accomplish this and the LHC (At peak) will eventually be dealing with 14 TeV of energy (though I've read reports, it can go up to a maximum of 17 TeV?)