By: Parisa Yan

We live on a planet named Earth, which belongs in the solar system. The solar system is in the Milky Way galaxy, which is in the universe. But how did the universe begin?

Scientists believe that our universe started in a big explosion. Edwin Hubble used a powerful telescope to find that galaxies are constantly moving away from each other, which led a Belgian astronomer named Georges Lemaltre to theorize that if the universe is expanding right now, then it should have been shrinking before. At around 13.8 billion years ago, there was an explosion (later known as the Big Bang) in which the universe was formed.

It was very hot and dense. Then it rapidly cooled down. It took 380,000 years for the first atoms to form as electrons were trapped into orbit around balls of protons and neutrons, or nuclei.

Well, then. About 13.6 billion years ago, our galaxy, the Milky Way, formed.

Much later, as seen in the diagram above, the sun and all its planets formed. Only one planet was suitable for life, and that was our Earth. The first cells formed 3.8 billion years ago, and humans only appeared 1.8 million years ago. That’s just a blink of an eye in the history of our universe.

Sources:

https://www.amnh.org/explore/ology/astronomy/how-did-the-universe-begin