The "Early Universe" refers to the initial moments after the Big Bang, approximately 13.8 billion years ago. During this time, the universe was extremely hot and dense, filled with fundamental particles like quarks and electrons. As it expanded, these particles began to cool and combine, forming protons and neutrons, which eventually led to the creation of simple atoms like hydrogen and helium. Within the first few minutes, a process called nucleosynthesis occurred, resulting in the formation of light elements. As the universe continued to expand and cool, it entered a phase known as the cosmic microwave background radiation, which provides a snapshot of the universe when it was just 380,000 years old.