Why are nebulas referred as the building blocks of the universe?

Nebulas are often referred to as the building blocks of the universe because they are vast clouds of gas and dust that serve as the primary sites for star formation. Within these regions, gravity pulls material together to form stars and planetary systems, essentially creating the fundamental components of galaxies. The elements produced in stars subsequently enrich the interstellar medium, contributing to the formation of new stars and planets, thus perpetuating the cycle of cosmic evolution.