The Big Bang Theory is the leading explanation for how the universe began. It suggests that around 13.8 billion years ago, the universe started as an incredibly hot and dense point, often called a singularity. This point then rapidly expanded, cooling down and allowing matter to form. Over time, this matter coalesced to create stars, galaxies, and eventually planets, including Earth. As the universe continues to expand, scientists study cosmic background radiation and the movement of galaxies to understand its origins better. This theory helps explain the distribution of galaxies and the abundance of elements like hydrogen and helium, which are crucial for the formation of stars and planets.